Kluane Lake Research Station Bibliography


The Kluane Lake Research Station Bibliography currently contains the following 161 Kluane Boreal Forest Ecosystem Project contributions, which are sorted here by contribution number.


Food supplementation experiments with terrestrial vertebrates : patterns, problems, and the future   /   Boutin, S.
(Canadian journal of zoology, v. 68, no. 2, Feb. 1990, p. 203-220)
(Kluane Boreal Forest Ecosystem Project contribution, no. 1)
References.
ASTIS record 53709.
Languages: English
Web: doi:10.1139/z90-031
Libraries: ACU

I reviewed 138 cases in which terrestrial vertebrates received supplemental food under field conditions. These cases are strongly biased toward small-bodied herbivores in north temperate environments. Most studies address population level questions and have supplied food over a short term (<1 year) and on a small spatial scale (to less than 50 individuals). Individuals receiving supplemental food usually had smaller home ranges, higher body weights, and advanced breeding relative to those on control areas. The typical population response to food supplementation was two- to three-fold increase in density, but no change in the pattern of population dynamics. In particular, food addition did not prevent major declines in fluctuating populations. Researchers have failed to examine behaviour of individuals under conditions of supplemental food when addressing questions of population regulation. This review points to the need for researchers to conduct food supplementation experiments in tropical environments, on a larger scale, and over longer periods of time. (Au)


Two-dimensional analysis of spatial pattern in vegetation for site comparison   /   Dale, M.R.T.
(Canadian journal of botany, v. 68, no. 1, Jan. 1990, p. 149-158, ill., maps)
(Kluane Boreal Forest Ecosystem Project contribution, no. 2)
Appendix.
References.
ASTIS record 53740.
Languages: English
Web: doi:10.1139/b90-020
Libraries: ACU

A new method for the analysis of spatial pattern in two dimensions is described. The technique uses data collected in square or rectangular grids of quadrats to examine the scale of pattern in vegetation, no matter how the grids are oriented with respect to the pattern. Its usefulness is demonstrated by application to artificial data. The method is also applied to vegetation classification data derived from LANDSAT TM satellite imagery of a valley in the Yukon, Canada, in which the effects of experimental manipulations on boreal communities are being studied. A set of 2 × 2 km squares of the valley were selected for analysis in which the vegetation composition squares varies considerably. The analysis shows that most of the squares had one and only one scale of two dimensional pattern, consistently in the range of 360-780 m. (Au)


An experimental study of the plant-arthropod-bird food chain in the southwestern Yukon   /   Folkard, N.F.G.   Smith, J. [Supervisor]
Vancouver, B.C. : Universiy of British Columbia, 1990.
viii, 105 leaves : ill., 2 maps ; 28 cm.
(ProQuest Dissertations & Theses publication, no. MM75414)
(Kluane Boreal Forest Ecosystem Project contribution, no. 3)
ISBN 97803157541410
Thesis (M.Sc.) - University of British Columbia, 1990.
Appendices.
Bibliography: p. 88-97.
ASTIS record 60572.
Languages: English
Libraries: BVAU OONL

I describe an experimental study of the importance of food limitation and predation at three trophic levels in a terrestrial food web. The study system was the herb layer vegetation-arthropod-insectivorous bird food chain in the boreal forest near Kluane Lake, southwestern Yukon. Since little is known about boreal bird communities, I conducted a descriptive study of the community of passerine and piciform birds at Kluane in addition to the main study. Variable circular plot point counts were used to estimate bird populations in 1987 through 1990. Species' habitat preferences, use of foraging substrates and diets were studied in 1988 and 1989. Population densities, species richness and evenness were all low. Yellow-rumped warblers (Dendroica coronata) and dark-eyed juncos (Junco hyemalis) dominated the community. Common species differed markedly in their habitat preferences, and showed generally low overlaps in their use of foraging substrates. There was little evidence of dietary specialization. There was rather little spatial variation in the community, and species composition and total density remained approximately the same through time. However, there were large fluctuations in some species' populations between 1987 and 1989. The experimental study was conducted at two scales. Chemical fertilizer was applied to two 570m x 570m areas in 1987, 1988 and 1989. I compared arthropod populations, bird populations and bird reproductive performance in these areas with those in two control areas. Two experiments using 5m x 5m plots were performed in 1988 to examine the effects of fertilization on plants and arthropods in more detail, and to study the responses of these trophic levels to the exclusion of passerine birds and mammalian herbivores. All three trophic levels responded positively to fertilization, but the results were variable and there were no very large increases in biomass or population size. Dark-eyed juncos nested one week earlier in fertilized areas, which may have enhanced their reproductive success. Passerine exclusion did not increase arthropod biomass, but exclusion of mammalian herbivores increased plant biomass. "Bottom-up" limitation by food appears to dominate this system, but "top-down" limitation also operates at at least one level. More work is needed to fully understand how the system functions. (Au)


Population dynamics of Clethrionomys and Peromyscus in southwestern Yukon 1973-1989   /   Gilbert, B.S.   Krebs, C.J.
(Holarctic ecology, v. 14, no. 4, Oct.-Dec. 1991, p. 250-259, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 4)
References.
ASTIS record 53775.
Languages: English
Web: doi:10.1111/j.1600-0587.1991.tb00659.x
Libraries: ACU

Clethrionomys rutilus and Peromyscus maniculatus occur together in the boreal forest of southwestern Yukon and we studied their population dynamics on unmanipulated live-trapping grids for 17 yr. Peromyscus showed a regular seasonal change in numbers each year with little interannual variation. Clethrionomys by comparison, showed low density fluctuations during one period (1976-1982) followed by changes, in number in the next period that are consistent with a typical 3-4 yr microtine cycle. During one of two years of peak numbers adult males had unusually heavy body weights. The sexual maturation of juvenile Clethrionomys varied inversely with density. In most years Clethrionomys showed higher rates of population increase from spring to late summer than Peromyscus and this may be partly attributed to the vole's longer breeding season. Juvenile female Clethrionomys often reached sexual maturity during their first summer when population density was low but Peromyscus never matured during their first summer. Finally, there was no correlation between the two species in year to year changes in overwinter survival rates. This is the first report of a cyclic North American population of Clethrionomys and it underlines the need to search for hypotheses of population regulation that explain both annual and multi-annual cycles within the same population. (Au)


An antifeedant in balsam poplar inhibits browsing by snowshoe hares   /   Jogia, M.K.   Sinclair, A.R.E.   Andersen, R.J.
(Oecologia, v. 79, no. 2, May 1989, p. 189-192, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 5)
References.
ASTIS record 53766.
Languages: English
Web: doi:10.1007/BF00388477
Libraries: ACU

The 'plant defense guild' hypothesis for the evolution of plant secondary chemicals predicts that plant species defend themselves against generalist herbivores such as the snowshoe hare (Lepus americanus) in the Canadian boreal forest by evolving unique antifeedant chemicals. Plant species may coevolve in an ecosystem by presenting an array of chemicals to herbivores. We report further evidence for this idea from the presence of 2,4,6-trihydroxydihydrochalcone in the CH2Cl2 extracts of Populus balsamifera juvenile twigs. These extracts, added to rabbit chow, were offered to hares in choice tests. The bioassay established that the chemical acted as an antifeedant for hares. (Au)


The influence of snow on lynx and coyote movements : does morphology affect behavior?   /   Murray, D.L.   Boutin, S.
(Oecologia, v. 88, no. 3, Nov. 1991, p. 463-469, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 6)
References.
ASTIS record 53767.
Languages: English
Web: doi:10.1007/BF00317707
Libraries: ACU

We studied sympatric lynx (Lynx canadensis) and coyotes (Canis latrans) to assess how morphological disadvantages to locomotion over snow affected movement patterns. Both species are of similar size and mass, but the feet of lynx are much larger, and coyotes were found to have 4.1-8.8 times the foot-load (ratio of body mass to foot area) of lynx. This resulted in greater mean sinking depths of coyote limbs, although the magnitude of the difference was less than that in foot-load. Coyotes exhibited stronger use of behavioral patterns that reduced negative effects of snow on movements. Coyotes were most abundant at low elevations where snow was shallow, whereas lynx were mostly at higher elevations. Coyotes also used areas at both elevations where snow was shallower than average, while lynx used areas where snow was deeper. Further, both species used travel routes where snow was shallower than it was near the track. Coyotes traveled on harder snow and used trails more frequently, thereby tending to reduce sinking depths to those similar to lynx. The behavioral repertoire of coyotes reduced the morphological advantage of large feet possessed by lynx; however, overall sinking depths were still greater in coyotes. Snowshoe hares (Lepus americanus) were the main prey of both species, and their foot-load was less than that of either predator. Hare kills by coyotes occurred after fewer bounds than did those by lynx, and the large difference between foot-loads of both species of predators may have forced coyotes to ambush rather than chase hares, as did lynx. (Au)


Hunting behaviour of a sympatric felid and canid in relation to vegetative cover   /   Murray, D.L.   Boutin, S.   O'Donoghue, M.   Nams, V.O.
(Animal behaviour, v. 50, no. 5, 1995, p.1203-1210, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 7)
References.
ASTIS record 53343.
Languages: English
Web: doi:10.1016/0003-3472(95)80037-9
Libraries: ACU

Carnivore foraging behaviour is suited for hunting in specific vegetative cover types and therefore is largely stereotypical within taxonomic families. Felids typically employ dense cover to stalk or ambush prey, whereas canids do not make use of vegetation when hunting. Sympatric lynx, Lynx canadensis, and coyotes, Canis latrans, were tracked in snow for three winters and hunting behaviour in relation to vegetative cover was examined. The major prey of both species was snowshoe hare, Lepus americanus. Lynx chased hares more frequently in sparse spruce, Picea glauca, canopy than coyotes, whereas coyotes chased hares more often in dense spruce than lynx. Lynx initiated chases by stalking in sparse spruce and by ambushing from beds in dense spruce. Vegetative cover did not affect lynx hunting success, but lynx did have higher success when ambushing versus stalking hares. Coyotes chased hares from closer proximity than lynx and employed a pouncing hunting behaviour. Coyote chases were shorter and more successful in dense versus sparse forest. It is concluded that lynx hunting behaviour is variable according to cover, whereas that of coyotes is fixed. However, coyotes appeared to use vegetation as concealment when approaching hares: the possible influence of snow on hunting tactics of each predator species is discussed. (Au)


Winter habitat selection by lynx and coyotes in relation to snowshoe hare abundance   /   Murray, D.L.   Boutin, S.   O'Donoghue, M.
(Canadian journal of zoology, v. 72, no. 8, Aug. 1994, p.1444-1451, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 8)
References.
ASTIS record 53720.
Languages: English
Web: doi:10.1139/z94-191
Libraries: ACU

We examined the relationship between winter habitat selection among lynx (Lynx canadensis) and coyotes (Canis latrans) and relative snowshoe hare (Lepus americanus) abundance by tracking in snow during three winters. Hare numbers were higher in dense spruce (Picea glauca) than in other habitats in 1987-1988, and both predator species selected that habitat in that year. In 1988-1989, hare distribution was similar among habitats, and both predators used spruce habitats relative to their availability. In 1989-1990, hare numbers were also similar among habitats, and lynx used spruce habitats according to availability, whereas coyotes selected dense spruce. Hares were the main prey of both species, and the distribution of hares chased and killed by lynx was similar to that predicted by habitat use. Lynx hunting success was also similar among habitats. In comparison, coyotes chased and killed more hares than expected and had higher hunting success in dense spruce. Snow was shallower and harder in all spruce habitats used by coyotes than in those travelled by lynx. This suggests that coyotes were more selective of snow conditions than lynx, probably as a result of their high foot-load (ratio of body mass to foot area) relative to that of hares. Coyotes scavenged more often than lynx, but neither species seemed to select habitats on the basis of carcass availability. We concluded that high hare densities influenced selection of dense spruce by both species in 1987-1988, and that coyotes may also have chosen habitats on the basis of hunting success and snow conditions. (Au)


Camphor from juvenile white spruce as an antifeedant for snowshoe hares   /   Sinclair, A.R.E.   Jogia, M.K.   Andersen, R.J.
(Journal of chemical ecology, v. 14, no. 6, 1988, p.1505-1514, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 9)
References.
ASTIS record 54172.
Languages: English
Web: doi:10.1007/BF01012422
Libraries: AEU

One theory in plant antiherbivore defense predicts that slow growing late succession plants like white spruce (Picea glauca) make large investments in antiherbivore defenses. Juvenile stages of white spruce in the Yukon, Canada, are rarely browsed by snowshoe hares (Lepus americanus), an abundant herbivore, but mature spruce is a highly preferred food. The hexane-soluble fractions of the methanol extracts from juvenile and mature white spruce contain camphor and bornyl acetate. There is four times as much camphor in juvenile spruce as in mature spruce from GC [gas chromatography] analysis. Plant extracts were added to rabbit chow. Pairs of extracts were offered to hares in choice tests. These tests demonstrated that camphor in the juvenile spruce extracts deterred feeding. Bornyl acetate did not have a clear antifeeding effect. (Au)


Aspects of winter foraging in lynx and coyotes from southwestern Yukon during an increase in snowshoe hare abundance   /   Murray, D.L.   Boutin, S. [Supervisor]
Edmonton, Alta. : University of Alberta, 1991.
155 leaves : ill. ; 29 cm.
(ProQuest Dissertations & Theses publication, no. MM66707)
(Kluane Boreal Forest Ecosystem Project contribution, no. 10)
ISBN 0-315-66707-5
Thesis (M.Sc.) - University of Alberta, Dept. of Zoology, Edmonton, Alta., 1991.
References.
ASTIS record 32315.
Languages: English
Libraries: XYKLRS AEU

Lynx (Lynx canadenis) and coyotes (Canis latrans) were studied during two winters in southwestern Yukon to examine how differences in morphology and behaviour interacted with snow conditions and prey density to affect habitat use and foraging in each species. Coyotes had 4.1 to 8.8 times the foot-load of lynx, but a similar chest height. Predators were tracked in snow for 645 km to determine their use of snow conditions, response to an increase in abundance of snowshoe hares (Lepus americanus) and habitat selection. Coyotes used primarily the low elevation region of the study site where there was less snow, and areas within both high and low elevation regions where snow was deeper than average. Conversely, lynx selected the high elevation region where snow was deeper, as well as areas within both high and low elevation regions where snow was deeper than average. Further, lynx were less prone to travel on snow-packed trails than coyotes. Hare densities doubled between years of study, and both predators increased their kill- and scavenging-rates by 1.6 and 2.2 fold respectively. Both predators selected spruce forests and avoided shrub and open areas, but lynx traveled more in areas of low spruce cover. Lynx did not select habitats with highest hare densities or with the lowest snow depth, and their ability to detect hares at long distances may have influenced their strong selection for open spruce forests. Coyotes chased hares a shorter distance than did lynx, and success rates were higher in areas of dense cover. Coyotes did not select dense cover areas, though most kills occurred therein. This study confirms that differences exist in the foraging patterns of two similarly-sized sympatric carnivores. (Au)


Methods of locating Great Horned Owl nests in the boreal forest   /   Rohner, C.   Doyle, F.I.
(The Journal of raptor research, v. 26, no. 1, Mar. 1992, p. 33-35)
(Kluane Boreal Forest Ecosystem Project contribution, no. 11)
References.
Resume also in Spanish.
This paper is a short communication.
ASTIS record 54027.
Languages: English
Libraries: SSU

... As part of a collaborative project on the boreal forest ecosystem, we are studying the Great Horned Owl at Kluane Lake, in the southwestern Yukon .... At first we had great difficulties finding nests, but we have now developed an efficient method. We describe this method here in the hope of encouraging research on these birds in northern areas. ... Step 1: Acoustic Triangulation of the Nesting Area. Great Horned Owl nests stand out in deciduous forests and can be detected over large areas with systematic searches from the air or from the ground in late winter .... In coniferous forests, such methods are not feasible because of the dense cover. In this case, the nesting area has to be pinpointed before a visual search can begin. The roosting and calling behavior of the male are the key to the location of the nesting area. We found that four radio-tagged males regularly roosted within 100 m of the incubating female. ... males begin their hooting close to the nest about 1 hr after sunset, and again hoot in the nesting area about 1 hr before sunrise when they settle down for the daytime. The females on the nest usually join the males with one to several hoots at the beginning and the end of each activity period. Triangulations on hooting birds during these specific times provide a preliminary location of the nest site. This then serves as a starting point for a detailed visual search of the area. Depending on the terrain and on the experience of the observers, one to several hooting sequences may be required to locate a nesting area accurately. Step 2: Visual Search for the Nest. Great Horned Owls in the Yukon breed mainly on "witches' brooms" (fungus-induced clumps of dense foliage in White Spruce Picea glauca), or they use old nests built by Red-tailed Hawks (Buteo jamaicensis) or Common Ravens (Corus corax). The incubating female is often not visible from the ground, and the large number of witches' brooms in our study area required careful visual inspection of almost all individual trees in a nesting area. In all 36 nests that we found by visual searches from 1988-91, we saw at least one down feather at the edge of the nest or in nearby branches. This was also true for 21 nests that were found by locating radio-tagged females and for 4 nest sites reused from previous years. We therefore conclude that the presence of fresh down feathers is the best visual cue to determine whether a witches' broom is used as Great Horned Owl nest or not. ... The method described is time-intensive but reliable. It enabled us to find 23 nests in 28 searched owl territories after 1-5 triangulations for step 1, and 0.5-5 hr searching time for step 2. After 5 hr of unsuccessful search we usually stopped the search until the time near fledging. At this stage the adults engage more aggressively in nest defense and are likely to hoot when an observer approaches close to a nest. A possible improvement to this method involves daytime playback of Great Horned Owl hoots. Males might reply from the roost, thereby revealing the nest location. We found one nest within minutes of using this method, but systematic trials using daytime playback during incubation in 1990 and 1991 showed that only 3 of 10 males responded. Perhaps playbacks could be applied more efficiently at particular stages of the breeding cycle and times of day (e.g., dawn). A concern over any new technique is the disturbance it causes to the animals. ... In our study, we have little evidence of observer disturbance. We approached more than 50 nests of 20 different pairs during incubation or with young nestlings, and only 6 females were flushed from the nest. Two broods failed, but we suspect that the very late breeding date and food shortage explained these failures. We therefore feel that the "triangulation-and-search" technique described here causes little disturbance. Further tests of playback methods may be useful to see if their efficacy can be enhanced, and if they can be used withou t disturbing the owls. (Au)


What drives the snowshoe hare cycle in Canada's Yukon?   /   Krebs, C.J.   Boonstra, R.   Boutin, S.   Dale, M.   Hannon, S.J.   Martin, K.   Sinclair, A.R.E.   Smith, J.N.M.   Turkington, R.
In: Wildlife 2001 : populations / Edited by D.R. McCullough and R.H. Barrett. - London ; New York : Elsevier Applied Science, 1992, p. 886-896, ill.
(Kluane Boreal Forest Ecosystem Project contribution, no. 12)
References.
Paper in the Proceedings of "Wildlife 2001: Populations", an International Conference on Population Dynamics and Management of Vertebrates (Exclusive of Primates and Fish), held at Oakland, California, USA, July, 29-30, 1991.
ASTIS record 54185.
Languages: English
Libraries: BVAU

Snowshoe hares (Lepus americanus) and their predators fluctuate cyclically in abundance every 9-11 years in the southwestern Yukon. Peak populations occurred in 1980-1981 and in 1989-90 around Kluane Lake. During the first cycle (1977-84) we tested food limitation hypotheses by providing three hare populations with supplemental food (rabbit chow). Extra food did not prevent the cyclic decline, and neither the timing nor the rate of the decline from 1981-84 was affected by food addition, in comparison with controls. During the second cycle (1986-present) we have been testing the predator hypothesis, and are trying to find out if there is an interaction between predators and food. We have constructed two mammalian predator exclosures (1 km²) and on one of these areas we are adding food. We have fertilized two large areas with nitrogen-phosphorus-potassium fertilizer to increase plant production, and we have added hare food to two unfenced areas as well. Within the next 4 years we should be able to evaluate the effects of these manipulations on the snowshoe hare cycle. (Au)


Effects of supplemental food on snowshoe hare reproduction and juvenile growth at a cyclic population peak   /   O'Donoghue, M.   Krebs, C.J.
(Journal of animal ecology, v. 61, no. 3, Oct. 1992, p. 631-641, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 13)
References.
ASTIS record 53351.
Languages: English
Web: doi:10.2307/5618
Libraries: ACU

Summary: 1. Snowshoe hare (Lepus americanus (Erxleben)) populations were provided with supplemental food on two study grids in the south-west Yukon to examine the effects of food on reproduction and juvenile growth. 2. Timing of parturition, pregnancy rates, litter sizes, male breeding condition, and juvenile growth rates were measured on two food grids and on two control grids during two summers at a cyclic peak in hare numbers. 3. Most female hares gave birth to three litters per summer, and parturition was in approximate synchrony, such that there were three distinct litter groups per season. 4. The main effects of food addition were to increase hare densities 2.1- to 2.7-fold, advance the timing of breeding by about 1 week in 1 year, and increase pregnancy rates by 5% relative to the controls. 5. There were no significant differences in litter sizes, lengths of male breeding seasons, juvenile growth rates, or total female reproductive output between hares on the food and control grids. 6. Third litter stillborn rates were higher, and third litter juvenile growth rates slightly lower on food grids relative to those on controls, possibly reflecting an effect of higher densities. 7. This study suggests that food is not a proximate factor limiting hare reproduction and early juvenile growth at the observed peak hare densities. (Au)


Early movements and dispersal of juvenile snowshoe hares   /   O'Donoghue, M.   Bergman, C.M.
(Canadian journal of zoology, v. 70, no. 9, Sept. 1992, p.1787-1791, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 14)
References.
ASTIS record 53717.
Languages: English
Web: doi:10.1139/z92-246
Libraries: ACU

Juvenile snowshoe hares (Lepus americanus) were radio-tagged at birth to examine predispersal movements, maternal-juvenile interactions, and timing of natal dispersal. Hare litters stayed at their natal sites for an average of 2.7 days, after which each individual usually found a separate hiding place from its littermates. Observations at natal sites suggested that adult female hares nursed their litters only once per day, shortly after twilight. Some females aggressively defended their newborn litters before the juveniles left the natal site. Juvenile hares ranged progressively further from their natal sites as they grew, up to the age of 20 days. From 20 to 35 days of age, leverets stayed approximately 75 m from their natal sites, after which time their movements again increased. Natal dispersal of juvenile hares began shortly after weaning at 24-28 days of age. Many third-litter juveniles were nursed for a longer period lasting at least 29-40 days. Juvenile males may disperse sooner and travel further than females from their natal ranges. (Au)


Food-stressed Great Horned Owl kills adult Goshawk : exceptional observation or community process   /   Rohner, C.   Doyle, F.I.
(The Journal of raptor research, v. 26, no. 4, Dec. 1992, p. 261-263)
(Kluane Boreal Forest Ecosystem Project contribution, no. 15)
References.
Resume also in Spanish.
This paper is a short communication.
ASTIS record 54028.
Languages: English
Libraries: SSU

Great Horned Owls (Bubo virginianus) can prey on other owl and diurnal raptor species up to the size of Northern Goshawks (Accipiter gentilis), and the question has been raised why this behavior occurs and whether it affects the structure of raptor communities .... During our study of avian predation in the boreal forest ecosystem near Kluane Lake in the southwestern Yukon ... we encountered circumstantial evidence for an owl predation of an adult female goshawk, which led us to a revised assessment of such interspecific killings among raptors. ... In our case, we present a single observation with additional information that shows potential links to causes and implications of this behavior: we will 1) try to estimate how rare such events were during our study, and 2) discuss how the documented details of the ecological context of both predator and prey relate to hypotheses on the evolution of interspecific killing among raptors. ... We monitored 17 goshawk nests during 1989-91 and found a maximum of two possible cases of Great Horned Owl predation on goshawks. ... Owl predation may rather affect the nest site selection than the population dynamics and density of other raptors. Predation by Great Horned Owls, however, has been reported to account for higher mortalities in other species: up to 30% of juvenile Spotted Owls ..., 65% of juvenile Great Gray Owls ..., 0-44% of Red-tailed Hawks ..., up to 27% of fledged or released Peregrine Falcons..., up to 21% of hatched Ospreys ..., 25 predations on young Harris' Hawks from 64 nests .... We found it interesting that the goshawk was killed by an owl under food stress, which we had induced experimentally. During our study, the overall prey base was high because Snowshoe Hares (Lepus americanus) were at the peak of their population cycle ... and the overall predation by owls on goshawks was low. ... Observations of raptors killing raptors have been considered anomalies. ... This perspective is based on the assumption that raptors are a costly prey because of the high risk of injury to an attacking predator. Why raptors kill other raptors despite the high costs involved, has been explained by the additional benefits of removing a potential competitor .... Benefits other than reduced competition for food may be reduced competition for nest sites, increased protection of young from predation, and increased protection from harassment .... The most parsimonious explanation is that raptors kill raptors simply to obtain food, or in other words, to obtain direct and immediate benefits. At the present state of our knowledge, we should take this simple explanation as a null-hypothesis, and our scientific effort should be directed toward testing it. ... A Great Homed Owl killing an adult goshawk was a rare event with little impact on the goshawk population during our study. The frequency of such predation may vary with prey abundance, however, and may be more pronounced when other prey is scarce. Based on detailed knowledge of the ecological situation of our case, we question the current perspective that raptors killing raptors are anomalies that involve a high risk and require competition as an explanation. More observations in a known context are needed to test hypotheses on why this phenomenon occurs. (Au)


A method to estimate travel distances of fast moving animals   /   Breitenmoser, U.   Breitenmoser-Würsten, C.   Zuleta, G.A.   Bernhart, F.   O'Donoghue, M.
In: Biotelemetry XII, Proceedings of the Twelfth International Symposium on Biotelemetry, Ancona, Italy, Aug. 31-Sept. 5, 1992 / Edited by P. Mancini, S. Fioretti, C. Cristalli, and R. Bedini. - Pisa, Italy : Litografia Felici, 1992, p. 318-326, ill.
(Kluane Boreal Forest Ecosystem Project contribution, no. 16)
References.
ASTIS record 20189.
Languages: English

We present a method to estimate daily travel distances (DTD) of lynx (Lynx canadensis) by means of telemetry. Lynx were located every 15 minutes for a maximum of 8 hours. Three observers simultaneously took 2 bearings each. A fourth person analyzed the locations on a computer and guided the observers. Later, the data were re-analyzed, and non-significant displacements excluded. DTD in summer was 12.9-13.5 km. From tracking series in winter, we derived a correction factor and estimated the real distance travelled to be about 20.1-21.1 km. By splitting the continuous location series into intervals of decreasing length, we determined a model to compute Dills. At a rhythm of 1 location/minute, the DTD would be 20.5 km. (Au)


Population declines in the snowshoe hare and the role of stress   /   Boonstra, R.   Singleton, G.R.
(General and comparative endocrinology, v. 91, no. 2, Aug. 1993, p. 126-143, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 17)
References.
ASTIS record 53733.
Languages: English
Web: doi:10.1006/gcen.1993.1113
Libraries: ACU

Every 10 years snowshoe hare populations across the boreal forest of North America go through a population cycle, culminating in a decline lasting 4 or more years. We tested the hypothesis that snowshoe hares during the decline are in poor condition and less able to respond to challenges in their environment by examining the stress response of male hares. Three groups from February and May, 1991 (the second year of the hare decline in the Yukon), were compared: baseline hares were collected to obtain resting hormone levels; control hares were wild animals caught at randomly placed sites: and fed hares were wild animals caught on supplementary fed areas. The latter two groups were sequentially bled to examine their response to dexamethasone (DEX) followed by adrenocorticotropic hormone (ACTH). Trapping and handling were stressful to the experimental hares as the initial blood levels of total and free cortisol levels were higher (especially in controls), testosterone levels were lower, and glucose levels were higher in experimental hares than in baseline hares. Control and fed hares showed similar total and free cortisol responses, falling to low levels after the DEX injection and increasing rapidly in response to the ACTH injection. However, control hares were in worse condition than fed hares as indicated by the higher free cortisol levels and lower maximum corticosteroid-binding capacity (MCBC) in control hares. In addition, though testosterone levels fell in both groups in response to DEX, only the fed hares showed a large, transitory increase 30 min after the ACTH injection. An unexpected finding was a dramatic increase in MCBC levels 30 min after the ACTH injection in both experimental groups, but it was more pronounced in the fed group. We conclude that the pituitary-adrenocortical feedback system in hares from declining populations is operating normally and that they should be able to cope with acute, short-term stressors, but that they are in poor condition and are exposed to higher levels of free cortisol than fed hares in good condition. (Au)


Patterns of predation in a Willow Ptarmigan population in northern Canada   /   Hannon, S.J.   Gruys, R.C.
(Kluane Boreal Forest Ecosystem Project contribution, no. 18)
Paper from the Proceedings of the Fourth [or 4th or IVth] International Grouse Symposium, Lam, West Germany, 28 September - 3 October 1987. / [Edited by T.W.I. Lovell and P.J. Hudson. - Reading, U.K. : World Pheasant Association, 1990?], p. 44-50, ill.
Indexed from a photocopy of the paper. No photocopy of the proceedings title was supplied.
References.
ASTIS record 32322.
Languages: English

Summary: 1. Sex, age, season of death, and identity of predation were determined for remains of 368 Willow Ptarmigan collected on breeding range over 8 years from a peak and declining population in northwestern British Columbia. Most remains were found at peak ptarmigan density, fewer in the decline, and least at low density. Similar numbers of birds were killed in spring and summer, and higher numbers were killed in fall/winter. 2. Of remains of known sex, 44% were hens and 56% were cocks. More males than hens were killed in spring but in proportion to their availability in winter. More hens than males were killed in summer during nesting and brood rearing. There was no difference in the proportion of males and females killed at different stages in the population cycle. 3. Yearlings were killed at similar rates in both sexes and in proportion to their availability in the population. 4. Kills by mammals and raptors were equally represented in the collection. Hens were killed more by raptors and cocks more by foxes. 5. The percentage of the kill made by mammals or raptors did not vary significantly by year, nor by stage of the ptarmigan population cycle. Numbers of foxes sighted varied considerably with most observed 2-3 years after the first year of peak Ptarmigan density. Raptors sightings were constant at the peak and during the decline, but were fewer in the low of the cycle. (Au)


Does risk of predation influence population dynamics? Evidence from the cyclic decline of snowshoe hares   /   Hik, D.S.
(Wildlife research, v. 22, no. 1, 1995, p. 115-129, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 19)
References.
ASTIS record 54163.
Languages: English
Web: doi:10.1071/WR9950115
Libraries: BVIV

Like most heavily preyed-upon animals, snowshoe hares (Lepus americanus) have to balance conflicting demands of obtaining food at a high rate and avoiding predators. Adopting foraging behaviors to minimise predation risk may also lead to a decline in condition, and hence fecundity. Predictions of three hypotheses (condition constraint hypothesis, predator-avoidance constraint hypothesis, predation-sensitive foraging (PSF) hypothesis) were tested by comparing changes in the survival and condition of snowshoe hares on four experimental areas in winter during a cyclic peak and decline (1989-1993) near Kluane Lake, Yukon, Canada, where (i) predation risk was reduced by excluding terrestrial predators (FENCE), (ii) food supply was supplemented with rabbit chow ad libitum (FOOD), (iii) these two treatments were combined (FENCE+FOOD), and (iv) an unmanipulated CONTROL was used. Different patterns of survival and changes in body mass were observed in the presence and absence of terrestrial predators. On the CONTROL area, female body mass and fecundity declined, even though sufficient winter forage was apparently available in all years. A similar decrease in body mass was observed on the FOOD treatment, but only during the third year of the population decline. In contrast, female body mass remained high throughout the decline in the absence of terrestrial predators in the FENCE+FOOD and FENCE treatments. Winter survival declined on CONTROL and FENCE areas during the first year of the population decline (1991), but remained higher on FOOD until 1992 and FENCE+FOOD until 1993. These results generally supported the PSF hypothesis where terrestrial predators were present (CONTROL and FOOD grids). Where terrestrial predators were absent (FENCE and FENCE+FOOD), the results supported the alternative condition constraint hypothesis. The evidence suggests that a cascade of sublethal behavioural and physiological effects associated with increased predation risk contribute to the population decline and delayed recovery of cyclic low-phase populations of snowshoe hares. (Au)


The experimental paradigm and long-term population studies   /   Krebs, C.J.
(Ibis, v.133, suppl. S1, Oct. 1991, p. 3-8)
(Kluane Boreal Forest Ecosystem Project contribution, no. 20)
References.
ASTIS record 53776.
Languages: English
Web: doi:10.1111/j.1474-919X.1991.tb07663.x
Libraries: ACU

Most ecologists recognize the value of long-term studies to population and community ecology, and many also subscribe to the experimental approach as the most effective way of obtaining ecological knowledge. But if we are experimentalists, do we need long-term studies? I argue that the answer to this question is yes, that we must combine these two approaches to solve the major ecological questions of the next century. Most of the challenging questions facing ecologists involve systems subject to long-term time trends or high environmental variability. Because of the statistical power of many ecological methods, long-term studies are essential to measure time trends in ecosystems. Ignoring statistical power has been a major problem with short-term studies, which have predominated in the ecological literature. Some examples of long-term studies on larch bud-moth, Zeiraphera diniana, winter moth, Operophthera brumata, and snowshoe hares are discussed briefly to illustrate the four major desiderata of long-term projects: spatial scale, sampling design, hypothesis testing and time-frame. Two reasons for not doing long-term studies are to assess density-dependence and to monitor ecosystem health. The density-dependent paradigm is bankrupt and has produced much argument and little understanding of population processes. Monitoring of populations is politically attractive but ecologically banal unless it is coupled with experimental work to understand the mechanisms behind system changes. (Au)


Diet choice and nutrition of captive showshoe hares (Lepus americanus) : interactions of energy, protein, and plant secondary compounds   /   Rodgers, A.R.   Sinclair, A.R.E.
(Écoscience, v. 4, no 2, 1997, p. 163-169, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 21)
References.
ASTIS record 53261.
Languages: English
Web: doi:10.1080/11956860.1997.11682391
Libraries: ACU

We examined consumption and digestibility of winter browse in captive snowshoe hares (Lepus americanus Erxl.) to determine how energy content, protein quality and plant secondary chemicals interact to affect their diet choice and nutrition. We found that preferred foods of snowshoe hares have higher apparent digestibilities of dry matter and energy than nonpreferred foods. Digested crude protein was unaffected by increased consumption of preferred foods, but declined when hares consumed nonpreferred foods. Rate of weight loss in hares increased with increasing consumption of nonpreferred twigs. Hares did not compensate for low protein or low energy content by eating more twigs. Weight changes were correlated with the energy content of the food and its digestibility, whereas consumption was correlated with phenol and protein content. If hares can increase consumption of preferred foods, they may simultaneously meet both their energy and protein requirements. If they are obliged to increase consumption of nonpreferred foods, then protein requirements may never be met due to the effects of secondary compounds. During periods of limited food availability, snowshoe hares should select a mixed diet that may include small quantities of poor-quality food items, regardless of preference, allowing them time to find good-quality foods. (Au)


Does nursery production reduce antiherbivore defences of white spruce? Evidence from feeding experiments with snowshoe hares   /   Rodgers, A.R.   Williams, D.   Sinclair, A.R.E.   Sullivan, T.P.   Andersen, R.J.
(Canadian journal of forest research, v. 23, no. 11, Oct. 1993, p.2358-2361)
(Kluane Boreal Forest Ecosystem Project contribution, no. 22)
References.
ASTIS record 54175.
Languages: English
Web: doi:10.1139/x93-290
Libraries: AEU

Previous studies indicate that snowshoe hares (Lepus americanus Erxleben) readily browse nursery-grown white spruce (Picea glauca (Moench) Voss) seedlings but tend to avoid naturally regenerating juvenile trees. We confirmed these observations in feeding trials with snowshoe hares and investigated several possible explanations for this phenomenon. In vitro digestibilities of nursery-grown and naturally regenerating white spruce seedlings were similar, indicating similar contents of acid detergent fibre. Thus, it is unlikely that snowshoe hares are better able to extract nutrients from nursery-grown seedlings than from naturally regenerating white spruce. We suggest that snowshoe hares prefer to feed on nursery-grown seedlings because they contain less camphor (a specific compound in white spruce shown to deter feeding by hares) and have higher nutritional value (i.e., nitrogen) than naturally regenerating plants. (Au)


Plant chemical defense and twig selection by snowshoe hare : an optimal foraging perspective   /   Schmitz, O.J.   Hik, D.S.   Sinclair, A.R.E.
(Oikos, v. 65, no. 2, Nov. 1992, p. 295-300, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 23)
References.
ASTIS record 53768.
Languages: English
Web: doi:10.2307/3545021
Libraries: ACU

We examined preferences of snowshoe hares for twigs of 2 winter forage plants: chemically defended balsam poplar Populus balsamifera, and comparatively less defended gray willow, Salix glauca. We used an optimal foraging model that explicitly incorporates the effects of secondary plant chemicals to predict foraging preferences of hares. The model predicted that the foraging preferences should be conditional: preference should depend on the ratio of digestible nutrient content in the defended and comparatively less defended plants relative to the ratio of the wet mass/dry mass of defended and comparatively less defended plants. We conducted a feeding experiment in which we presented hares fresh twigs of P. balsamifera and S. glauca (controls). We also manipulated the wet mass/dry mass ratio and nutrient contents of P. balsamifera and S. glauca twigs to alter the above condition. (1) Drying the P. balsamifera twigs, to reduce their wet mass/dry mass ratio, resulted in a two fold increase in their consumption while the consumption of the undried, S. glauca remained similar to control levels. The efficacy of the plant defense was predictably reduced. (2) Consistent with model predictions, we reversed this behavior by presenting hares with dried twigs of both species. In this case, consumption did not differ from control levels indicating the defense was again effective. (3) The defense was also rendered less effective against hare browsing by increasing the nitrogen content of P. balsamifera twigs. It appears that hares do not exclusively select twigs to maximize the intake of a limiting nutrient or avoid plants containing secondary compounds. Preference is conditional upon the relative nutritional, physical and chemical attributes of highly defended and less defended browse species available in a habitat. (Au)


Can the solar cycle and climate synchronize the snowshoe hare cycle in Canada? Evidence from tree rings and ice cores   /   Sinclair, A.R.E.   Gosline, J.M.   Holdsworth, G.   Krebs, C.J.   Boutin, S.   Smith, J.N.M.   Boonstra, R.   Dale, M.
(American naturalist, v.141, no. 2, Feb. 1993, p. 173-198, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 24)
References.
ASTIS record 53366.
Languages: English
Libraries: ACU

Dark marks in the rings of white spruce less than 50 yr old in Yukon, Canada, are correlated with the number of stems browsed by snowshoe hares. The frequency of these marks is positively correlated with the density of hares in the same region. The frequency of marks in trees germinating between 1751 and 1983 is positively correlated with the hare fur records of the Hudson Bay Company. Both tree marks and hare numbers are correlated with sunspot numbers, and there is a 10-yr periodicity in the correlograms. Phase analysis shows that tree marks and sunspot numbers have periods of nearly constant phase difference during the years 1751-1787, 1838-1870, and 1948 to the present, and these periods coincide with those of high sunspot maxima. The nearly constant phase relations between the annual net snow accumulation on Mount Logan and (1) tree mark ratios, (2) hare fur records before about 1895, and (3) sunspot number during periods of high amplitude in the cycles suggest there is a solar cycle-climate-hare population and tree mark link. We suggest four ways of testing this hypothesis. (Au)


Triterpene constituents of the dwarf birch, Betula glandulosa   /   Williams, D.E.   Sinclair, A.R.E.   Andersen, R.J.
(Phytochemistry, v. 31, no. 7, July 1992, p.2312-2324, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 25)
References.
ASTIS record 53773.
Languages: English
Web: doi:10.1016/0031-9422(92)83272-Z
Libraries: ACU

Juvenile stages of the dwarf birch, Betula glandulosa, from the Yukon, Canada, are rarely browsed by snowshoe hares (Lepus americanus). Chemical investigation of extracts of B. glandulosa which strongly deter browsing by snowshoe hares has led to the isolation and structure determination of the new metabolite, deacetoxypapyriferic acid. Dammar-24-ene-12ß-O-acetyl-20(S)-ol-3-one, a previously unknown natural product, was obtained from extracts which did not deter browsing. The known metabolite papyriferic acid was found to be a minor constituent of extracts of B. glandulosa. (Au)


Autumn and winter movements and mortality of Willow Ptarmigan at Chilkat Pass, B.C.   /   Gruys, R.C.   Hannon, S.J. [Supervisor]
Edmonton, Alta. : University of Alberta, 1991.
182 leaves : ill., maps ; 28 cm.
(ProQuest Dissertations & Theses publication, no. MM66694)
(Kluane Boreal Forest Ecosystem Project contribution, no. 26)
ISBN 0-315-66694-8
Thesis (M.Sc.) - University of Alberta, Dept. of Zoology, Edmonton, Alta., 1991.
Appendices.
References.
ASTIS record 32312.
Languages: English
Libraries: AEU XYKLRS

I studied the timing and extent of movements and mortality of adult willow ptarmigan at Chilkat Pass, B.C. during autumn and winter. Radio-tagged ptarmigan did not leave their breeding grounds immediately after broods broke up, but remained on or near their territories until December. After chicks fledged, part of the population moved uphill from their territories. In late September, coincident with molt into winter plumage, ptarmigan moved farther from their territories. Both movements were presumably to areas with better cover and/or food. Once they molted, all tagged adult males and half of the tagged females returned to their territories, and males resumed territorial display. Ptarmigan remained on their territories until increasing snow cover depleted food and cover, forcing them to leave. Males left the breeding grounds later than females, and returned earlier in spring. In winter females moved farther than males, but several males moved as far as females. Natural autumn and overwinter mortality of adult males and females was similar in both years of the study. Adult females suffered most mortality during autumn raptor migration and on their wintering grounds. Adult males were killed during autumn and spring raptor migrations, as well as on the wintering grounds. Birds wintering in subalpine and forested habitats suffered similar mortality. During the breeding season female mortality ranged between 5 and 26%, mostly during incubation and after chicks hatched. In contrast, males suffered negligible mortality after they settled on their territories. Hence, differential mortality between the sexes occurred during the breeding season. Hunting mortality of banded birds was less than 20% in each of ten years. Banded males and females suffered similar hunting mortality each year. Among unbanded birds, males predominated in the hunters' bags even when females were still in the areas frequented by hunters. Hence, sex and age ratios from hunters' bags are an inaccurate estimator of true composition. (Au)


Effects of nitrogen fertilization on several woody and nonwoody boreal forest species   /   Nams, V.O.   Folkard, N.F.G.   Smith, J.N.M.
(Canadian journal of botany, v. 71, no. 1, Jan. 1993, p. 93-97, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 27)
References.
ASTIS record 53734.
Languages: English
Web: doi:10.1139/b93-011
Libraries: ACU

The effects of three levels of fertilizer were tested on the growth of several woody and nonwoody plants from a boreal forest community in southwestern Yukon. The effects of fertilization were assessed by clipping ground layer vegetation and measuring twig growth at the end of the second summer. Over the 2 years of fertilization there were significant increases in growth over control levels for perennial grasses (Festuca altaica and Calamagrostis lapponica), two herbs (Epilobium augustifolium and Achillea millefolium), and two deciduous shrubs (Salix glauca and Betula glandulosa). However, the growth of white spruce trees (Picea glauca) increased only slightly in response to increasing nitrogen levels, and the evergreen dwarf shrub Arctostaphylos uva-ursi showed no response. (Au)


Response of Great Horned Owls to manipulations of prey densities in the boreal forest   /   Rohner, C.
(The Journal of raptor research, v. 27, no. 1, Mar. 1993, p. 79-80)
(Kluane Boreal Forest Ecosystem Project contribution, no. 28)
Abstract only.
ASTIS record 54029.
Languages: English
Libraries: SSU

Foraging theory and models of territoriality predict that an animal will travel less when food is abundant and that its home range size will decrease. This concept is often applied to interpret movement and home range data in wildlife biology, although little experimental evidence exists for larger animals. A collaborative project near Kluane Lake in the southwestern Yukon was designed to investigate the interactions of animal populations of different tropic levels in the boreal forest ecosystem. Experimental food additions to snowshoe hares and ground squirrels resulted in up to 20 times higher densities on areas of 0.5-1 km². Two owls on territories with increased prey levels were chosen as experimental birds and radiotelemetry was used to compare them to 4 controls. Despite the extreme contrast in prey base, no differences in movement rates and home range sizes were apparent. This suggests caution for the general use of these measures as standard management tools. Can the sampling be refined, or does the concept not apply to our organisms? This question is open at the moment. One explanation is that the predictions from theory have been derived for an animal that searches randomly through homogeneous habitat. Great horned owls as typical perch hunters seem to be using a network of distinct hunting spots, rather than diffuse searching. The response would, therefore, not be strictly area dependent, but dependent on the specific location of these "hot spots" in the territory - a model that may also apply to other perch-hunting owls and raptors. A link to another result is interesting: during the course of a snowshoe hare cycle, the size of long-term territories was determined by intruder pressure, and not by food. Great horned owls, as a long-lived species, may try to maintain as large territories as possible in every situation. (Au)


Nitrogen fertilization stimulates herbivory by snowshoe hares in the boreal forest   /   Nams, V.O.   Folkard, N.F.G.   Smith, J.N.M.
(Canadian journal of zoology, v. 74, no. 1, Jan. 1996, p. 196-199, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 29)
References.
ASTIS record 53302.
Languages: English
Web: doi:10.1139/z96-024
Libraries: ACU

We fertilized small plots in the boreal forest of the southwestern Yukon, Canada, to see how herbivory was affected. We assessed snowshoe hare (Lepus americanus) activity by counting pellets, and estimated grazing on grass as the proportion of blades eaten. After 2 years of fertilization, snowshoe hares spent more time on and near the test plots with more fertilizer. More grass was grazed on those plots but not near them. Thus, herbivores were attracted to the general area of the fertilized plots but only grazed directly on the plots. (Au)


Autumn and winter movements and sexual segregation of Willow Ptarmigan   /   Gruys, R.C.
(Arctic, v. 46, no. 3, Sept. 1993, p. 228-239, ill., 1 map)
(Kluane Boreal Forest Ecosystem Project contribution, no. 30)
References.
ASTIS record 33049.
Languages: English
Web: http://pubs.aina.ucalgary.ca/arctic/Arctic46-3-228.pdf
Web: doi:10.14430/arctic1347
Libraries: ACU

Ptarmigan (Lagopus lagopus alexandrae) in northern British Columbia leave their breeding areas during autumn and winter. The movements differ between males and females. In this study I examine the causes and extent of these differences. Ptarmigan did not leave their breeding grounds immediately after the breeding season, but remained on or near their territories until December. After chicks fledged, part of the population moved uphill from their territories. Coincident with moult into winter plumage, ptarmigan moved farther from their territories. Both movements were probably to areas with better protection against predators. After moulting, all tagged males and half of the tagged females returned to their territories, and males resumed territorial display. Ptarmigan remained on their territories until increasing snow cover depleted cover, forcing them to leave. Males left the breeding grounds later than females and returned earlier in spring. In winter females moved farther than males, supporting the reproductive strategy hypothesis, but segregation was not complete. Sexual segregation may not be related to migration alone, but could occur at any time ptarmigan are in flocks. (Au)


Sex determination of hunter-killed and depredated Willow Ptarmigan using a discriminant analysis   /   Gruys, R.C.   Hannon, S.J.
(Journal of field ornithology, v. 64, no. 1, Winter 1993, p. 11-17)
(Kluane Boreal Forest Ecosystem Project contribution, no. 31)
References.
Spanish abstract provided.
ASTIS record 53782.
Languages: English
Libraries: ACU

A method of determining the sex from remains (only wings, primaries and/or rectrices available) of adult and yearling Willow Ptarmigan that were killed by predators or hunters is described. Measurements of wing chord, and length of outer rectrix, and primaries 8 and 9 were taken from live birds of known sex and age in spring. A discriminant analysis using a model incorporating wing chord and rectrix length best separated the sexes in the reference collection. Models incorporating wing chord and length of primary 8, or rectrix length and length of primary 8 were less reliable. With all models, however, over 80% of birds were correctly classified to sex. Similar results were obtained when the discriminant functions were used to classify birds of known sex and age that were killed by predators or hunters. Feather wear, however, as well as selective killing of large and small birds by hunters and predators, respectively, may affect accuracy of classification. (Au)


The numerical response of Great Horned Owls to the snowshoe hare cycle in the boreal forest   /   Rohner, C.   Krebs, C.J. [Supervisor]
Vancouver, B.C. : University of British Columbia, 1994.
x, 163 p. : ill. ; 28 cm.
(ProQuest Dissertations & Theses publication, no. NN95389)
(Kluane Boreal Forest Ecosystem Project contribution, no. 32)
ISBN 0-315-95389-6
Thesis (Ph.D.) - University of British Columbia, Vancouver, B.C., 1994.
References.
Indexed from microfiche.
ASTIS record 60517.
Languages: English
Libraries: BVAU XYKLRS

Great horned owls (Bubo virginianus) are among the most opportunistic avian predators. In the subarctic boreal forest, their diet consists mainly of snowshoe hares (Lepus americanus), which show extreme population cycles with a 8-11 year period. The aim of this thesis was to study the population ecology of great horned owls in a cyclic environment, to investigate the components of the numerical response of this predator to its prey, and to evaluate the evolutionary context of the ecological processes involved. The study was conducted from 1989-92, with some data from 1988 and 1993, at Kluane Lake in the southwestern Yukon, Canada. During the increase phase of the snowshoe hare cycle, 86% of resident owl pairs bred and raised large broods of 2.4-2.6 fledglings per successful nest. Survival of young owls in their first two years of life was high, and two females were observed to breed as yearlings. Densities of territorial owls almost doubled to a maximum of 21-24 pairs/100 km² from 1988-92, but most owls that recruited locally became non-territorial 'floaters', presumably because social behaviour limited the number of territories. Floaters were silent, their ranges overlapped with those of territorial birds, and their density reached 40-50% of the total population. Snowshoe hares began to decline in the winter of 1990/91, and the number of great horned owls recruited in fall dropped from 1.7/pair in 1989-90 to 0.3/pair in 1991. Proximate causes of high pre-dispersal mortality included predation by mammals and parasitism by black flies (Simuliidae) and by Leucocytozoon ziemanni, a blood parasite transmitted by these flies. Post-dispersal mortality and emigration of resident owls also increased as hare densities declined further, floaters being affected before territorial birds. Owl densities continued to increase after the hare peak and then declined with a time lag of one year for floaters, and two years for territory holders. Responses to brood size manipulations and food additions suggested that food was not super-abundant during the prey peak. I conclude that territorial behaviour is essential in causing time lags, with some birds monopolizing resources and conserving energy by ceasing reproduction. A review of life history variation in northern owls showed that great horned owls are constrained in their phenotypic plasticity to increase reproduction at high prey levels compared to some other species. Based on a comparison of evolution in the genera Bubo and Nyctea, I hypothesize that habitat-specific differences in the availability of prey during reproduction, and also in the mortality on age classes during bottlenecks, favoured the diversity of life histories in northern owls. (Au)


Predators of cyclic prey : is the Canada lynx victim or profiteer of the snowshoe hare cycle?   /   Breitenmoser, U.   Slough, B.G.   Breitenmoser-Würsten, C.
(Oikos, v. 66, no. 3, Apr. 1993, p. 551-554)
(Kluane Boreal Forest Ecosystem Project contribution, no. 33)
References.
ASTIS record 53769.
Languages: English
Web: doi:10.2307/3544952
Libraries: ACU

Most populations of predators of cyclic prey fluctuate as their reproductive output and survival is a function of prey availability. The predator's response to a given prey density, however, may alter from the increase to the decrease phase. In cycles, the development of the prey population is predictable, and more sophisticated strategies can evolve. We develop an hypothesis on the life history strategy of the Canada lynx (Lynx canadensis). We propose that resident lynx form a core population and occupy large and stable home ranges throughout the cycle. Their reproductive output is maximized with increasing prey availability, but reduced in the decline phase before the investment threatens the long-term survival of the residents. (Au)


Owl predation on snowshoe hares : consequences of antipredator behaviour   /   Rohner, C.   Krebs, C.J.
(Oecologia, v.108, no. 2, Oct. 1996, p. 303-310, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 34)
References.
ASTIS record 53272.
Languages: English
Web: doi:10.1007/BF00334655
Libraries: ACU

We show evidence of differential predation on snowshoe hares (Lepus americanus) by great horned owls (Bubo virginianus) and ask whether predation mortality is related to antipredator behaviour in prey. We predicted higher predation on (1) young and inexperienced hares, (2) hares in open habitats lacking cover to protect from owl predation, and (3) hares in above average condition assuming that rich food patches are under highest risk of predation. Information on killed hares was obtained at nest sites of owls and by monitoring hares using radio-telemetry. The availability of age classes within the hare population was established from live-trapping and field data on reproduction and survival. Great horned owls preferred juvenile over adult hares. Juveniles were more vulnerable to owl predation before rather than after dispersal, suggesting that displacement or increased mobility were not causes for this increased mortality. Owls killed radio-collared hares more often in open than in closed forest types, and they avoided or had less hunting success in habitats with dense shrub cover. Also, owls took hares in above average condition, although it is unclear whether samples from early spring are representative for other seasons. In conclusion, these results are consistent with the hypothesis that variation in antipredator behaviours of snowshoe hares leads to differential predation by great horned owls. (Au)


What is wrong with error polygons?   /   Nams, V.O.   Boutin, S.
(The Journal of wildlife management, v. 55, no. 1, Jan. 1991, p. 172-176, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 35)
Appendix.
References.
ASTIS record 53765.
Languages: English
Web: doi:10.2307/3809255
Libraries: ACU

The error polygon technique for measuring telemetry error is invalid for estimating precision of individual location estimates when >2 bearings are used; it is valid only for estimating average precision over many triangulations. When 2 bearings are used, it is valid for both individual and mean error estimates. (Au)


Effects of radiotelemetry error on sample size and bias when testing for habitat selection   /   Nams, V.O.
(Canadian journal of zoology, v. 67, no. 7, July 1989, p.1631-1636, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 36)
References.
ASTIS record 53708.
Languages: English
Web: doi:10.1139/z89-233
Libraries: ACU

Radiolocations of animals by triangulation have certain errors. I show how the ratio of telemetry error to habitat size affects efficiency of testing for habitat selection and how to estimate sample size when telemetry error is large. When telemetry error is more than 1.5 times average habitat size, the required sample size increases immensely. When telemetry error is large, measurements of habitat selection are biased. I present a technique to remove the bias and estimate the habitat selection one would observe if telemetry error were zero. (Au)


Predation risk and the 10-year snowshoe hare cycle   /   Hik, D.S.   Sinclair, A.R.E. [Supervisor]
Vancouver, B.C. : University of British Columbia, 1994.
x, 140 p. : ill. ; 28 cm.
(ProQuest Dissertations & Theses publication, no. NN89424)
(Kluane Boreal Forest Ecosystem Project contribution, no. 38)
ISBN 0-315-89424-5
Thesis (Ph.D.) - University of British Columbia, Vancouver, B.C., 1994.
Indexed from a PDF file acquired from ProQuest Dissertations & Theses.
References.
ASTIS record 60352.
Languages: English
Libraries: OONL XYKLRS

I examined the effects of predation risk on the behaviour and population dynamics of snowshoe hares (Lepus americanus) during a cyclic peak and decline (1989-1993) near Kluane Lake, Yukon. Like most heavily preyed upon animals, snowshoe hares have to balance conflicting demands of obtaining food at a high rate and avoiding predators. The consequences of adopting predator avoidance behaviours under high risk of predation in winter may influence population dynamics of hares. Changes in patterns of winter habitat use, survival, body mass, and female reproduction were compared on four experimental areas: (i) where predation risk is reduced by excluding-out terrestrial predators (FENCE), (ii) where food supply was supplemented with ad lib rabbit chow (FOOD), (iii) a combination of these two treatments (FENCE + FOOD), and (iv) an unmanipulated CONTROL. Three hypotheses were compared. The food hypothesis predicts that hares use habitats with the highest amounts of food: body mass remains high, but survival is reduced. The predator avoidance hypothesis predicts that hares use habitats with the lowest risk: survival is high, but body mass decreases. The predation-sensitive foraging (PSF) hypothesis predicts that both survival and body mass decline because a trade-off exists between predation risk and food availability. At peak densities hares used open habitats where food was readily available. However, as predation risk increased during the population decline, hares increased their use of safer, closed habitat and shifted their diet to include a greater proportion of poorer quality spruce twigs. This change in behaviour resulted in lower female body mass and reduced fecundity on the CONTROL area, even though sufficient winter forage was available. A similar decrease in body mass was observed on the FOOD treatment during the third year of the population decline. On FENCE + FOOD, female body mass and fecundity remained high during the decline. Similarly, bodymass did not decline on the FENCE treatment. These results supported the PSF hypothesis where terrestrial predators were present (CONTROL and FOOD), and the food hypothesis where terrestrial predators were absent (FENCE and FENCE + FOOD). Hares appear to have a limited ability to reduce exposure to predators because they have no absolutely safe refuge from predators, and they have limited reserves of energy during winter. Preliminary evidence suggests that physiological stress associated with high risk and poor condition is elevated during the population decline. I suggest that deleterious maternal effects mediated by predation risk may introduce a lag of one generation into the 10-year population cycle of snowshoe hares. (Au)


Hare-raising encounters : unexpected dangers lurk in the Yukon for baby snowshoe hares   /   O'Donoghue, M.   Stuart, S.
(Natural history, v.102, no. 2, Feb. 1993, p. 26-33, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 39)
ASTIS record 53369.
Languages: English
Libraries: ACU

... Our study of the ecology of juvenile snowshoe hares began in 1989, in Canada's Yukon Territory. Our work was part of the Kluane Boreal Forest Ecosystem Project, a cooperative research effort of three Canadian universities, whose aim is to examine the structure of the vertebrate community in the coniferous forests of the north. Our 125-square-mile study area was typical of boreal habitats found across a broad band of Canada, Alaska, and Eurasia. Spruce forest, broken occasionally by small natural clearings and aspen stands, dominated the landscape. A patchy and often dense understory of willows and bog birch provided ideal cover for the hares. Throughout the northern part of their range in Canada and Alaska, snowshoe hare demographics undergo dramatic fluctuations at fairly regular intervals. These fluctuations are often referred to as the ten-year cycle because the hare populations reach very high densities (one to four hares per acre) every eight to eleven years, almost simultaneously across North America. Then, over the next few years, hare populations plummet. They fall as low as about one hare per 200 acres and stay at that level for several years, after which the cycle begins again. This cycle is central to the functioning of the boreal community. As hare numbers rise and fall, so do the numbers of their predators, although predator numbers generally don't begin to decline until a year or so after the collapse of the hare population. Other boreal herbivore populations, such as grouse and squirrels, may also be affected by changes both in predator numbers and in the amount of food available after hare browsing. Researchers vary in their explanations of why the hare cycle occurs - some support a predator-prey cycle, others cite a hare-vegetation interaction. All major studies, however, have noted the same demographic changes in hare populations over the course of the cycle. Whether in the Yukon, in Alberta, or in Minnesota, the survival rate of juveniles isthe single most important factor responsible for increases or decreases in the hare population. However, the rate of juvenile survival measured in previous studies was always of hares older than one month. Younger hares were very difficult to find in the field and did not enter the live-traps set by biologists. The purpose of our research was to determine the survival rates of hares from birth through their first days and weeks and to investigate their ecology. ... we kept a round-the-clock watch at the birth sites of several mother hares to determine how and when their young were fed after their litters had broken up. ... The behavior of young hares and their mothers makes a great deal of sense when considered as a defense against predators. The answers we have found, however, have left us with many new questions. Do squirrels prey extensively on leverets only when they are abundant? Does this predation have a significant effect on the hare cycle, or would most of the leverets have been killed later by other predators anyway? To answer these and other questions, we will need to return to the boreal woods at different points in the hare cycle and see how the leverets fare then. But we are sure that for baby snowshoe hares, the forest will always be full of danger. (Au)


Investigation of causes of the 10-year hare cycle   /   Trostel, K.A.   Sinclair, T. [Supervisor]
Vancouver, B.C. : Universiy of British Columbia, 1986.
viii, 109 leaves : ill. ; 28 cm.
(ProQuest Dissertations & Theses publication, no. ML40022)
(Kluane Boreal Forest Ecosystem Project contribution, no. 40)
ISBN 0315400226
Thesis (M.Sc.) - University of British Columbia, 1986.
Appendices.
Bibliography: p. 81-85.
ASTIS record 60573.
Languages: English
Libraries: BVAU OONL XYKLRS

This thesis combined data from a trapping and radio-telemetry study of snowshoe hares at Kluane Lake, Yukon from January 1984 through August 1985 with data collected at the same site from 1977-83 (Boutin et al. 1986; Krebs et al. 1986) to examine possible causes for the 10-year cycle in density of snowshoe hares. In Chapter 2 I used data on causes of mortality, from a radio-telemetry study of a cyclic snowshoe hare population during 1978-84, to consider the importance of predation in causing the hare cycle. I found that predation during winter was the largest source of mortality for snowshoe hares during 1978-84. There was a 1-year lag in the response of predation mortality to changing hare density. There was a 2-year lag in the response to changing density of mortality due to causes other than predation. I incorporated this information on causes of mortality into a simulation model, to see whether observed predation mortality can cause changes in density similar to those of a cyclic population. I fitted the predation mortality data to a function in which total predator response consists of a Type II functional response and a delayed density-dependent numerical response. Using a simulation model that predicted mortality rates with this function, I produced 8-11 year cycles within parameter values measured in this study. In Chapter 3 I compared a non-cyclic snowshoe hare population on Jacquot Island in Kluane Lake, with a cyclic population on the mainland, 40 km to the SE. I used trapping data from both mainland and island sites, for a period that included population increase, peak, and decline (1977-85) to test hypotheses of conditions sufficient to cause a hare population cycle. I also presented results from a radio-telemetry study, conducted on both mainland and island during a population low on the mainland (1984-85). The hypothesis that high rates of recruitment followed by low rates of recruitment, is sufficient to cause a cycle was not supported. Data presented were consistent with hypotheses that any one of the following conditions was sufficient to cause the hare cycle: 1. High rates of survival followed by low rates of survival, particularly of juveniles; 2. Delayed density-dependent predation; 3. Periodic food shortage. (Au)


Finding mammals using far-infrared thermal imaging   /   Boonstra, R.   Krebs, C.J.   Boutin, S.   Eadie, J.M.
(Journal of mammalogy, v. 75, no. 4, Nov. 1994, p.1063-1068, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 41)
References.
ASTIS record 53778.
Languages: English
Web: doi:10.2307/1382490
Libraries: ACU

We examined the utility of far-infrared thermal imaging devices to detect and census mammals in the field. We used a Thermovision 210© to survey individuals, nests, or burrows of red squirrels (Tamiasciurus hudsonicus), Arctic ground squirrels (Spermophilus parryii), snowshoe hares (Lepus americanus), and meadow jumping mice (Zapus hudsonius). Using far-infrared thermal imaging, we successfully detected free-ranging red squirrels, snowshoe hares, and meadow jumping mice. Thermal imaging also was highly successful in determining activity at nests or burrows of Arctic ground squirrels. Far-infrared thermal imaging, however, was not useful in detecting active nests of red squirrels. These differences are largely attributable to variation among species in the insulative property of nests or fur. We review some of the limitations of far-infrared thermal imaging and conclude that it may provide a useful tool for certain ecological field studies. (Au)


A comparison of songbird censusing techniques at Kluane Lake, Yukon   /   Huggard, D.J.   Smith, J.N.M. [Supervisor]
Vancouver, B.C. : University of British Columbia, 1988.
v, 78 leaves : ill., maps ; 29 cm.
(Kluane Boreal Forest Ecosystem Project contribution, no. 42)
Thesis (B.Sc.) - University of British Columbia, Vancouver, B.C., 1988.
Appendices.
References.
ASTIS record 62050.
Languages: English
Libraries: XYKLRS

The songbird community in the boreal forest near Kluane Lake, Yukon, was censused using direct (territory mapping and sample plots) and indirect techniques (line transects and point counts). The direct methods give accurate estimates of songbird densities, but are extremely time-consuming. Indirect methods allow a greater area to be censused in a short time, and are needed for large-scale avian studies planned in the area, but they can produce erroneous estimates. In this study, the indirect censusing methods were compared in terms of their accuracy relative to the results from direct techniques. The consistency of the indirect methods was also determined using the various techniques available to analyze census data. Point counts were more accurate and showed interspecific and intraspecific differences more consistently than line transects. Four major assumptions needed to analyze data from indirect censuses were tested and found to be violated substantially by the methods, particularly line transects. Environmental and temporal factors affecting the census results were also examined. Based on these considerations, the point count method was recommended for future songbird studies in this and similar communities. Specific recommendations for conducting songbird censuses and minimizing violations of the assumptions are presented. (Au)


Do lemming, vole, and snowshoe hare cycles affect other small birds and mammals in northern ecosystems? [ Est-ce que les cycles des lemmings, des campagnols et des lièvres blancs ont un effet sur les petits oiseaux et d'autres espèces de mammifères dans les écosystèmes nordiques?]   /   Stuart-Smith, K.
(Student research in Canada's North : proceedings of the Third National Student Conference on Northern Studies, Ottawa, October 23-24, 1991 / Edited by W.O. Kupsch and J.F. Basinger. Musk-ox, no. 39, special publication, 1992, p. 181-188)
(Kluane Boreal Forest Ecosystem Project contribution, no. 43)
References.
ASTIS record 34134.
Languages: English
Libraries: ACU

The population cycles of small mammals (lemmings, voles, and snowshoe hares) and their predators in northern regions have been relatively well documented, but the effect of these cycles on other small herbivores (alternative prey) is largely unappraised. There is some evidence that alternative prey species also undergo population cycles, roughly synchronous with those of the main prey. These synchronous cycles may be generated through varying predation pressure by shared predators (the Alternative Prey Hypothesis). I reviewed the evidence for this hypothesis from studies on potential alternative prey species. All studies reviewed found breeding success or density of alternative prey to decrease as main prey declined from high to low density, but only twelve of twenty studies actually measured predation rates on alternative prey, and only three examined the effects of food, parasites, or weather on alternative prey. Declines in alternative prey may be due all, or in part, to these factors, rather than to predation. The Alternative Prey Hypothesis should be tested by manipulating predators and measuring rates of predation on alternative prey, and by evaluating the impact of other biotic and abiotic factors on alternative prey. (Au)


Population responses of Northern Goshawks to the 10-year cycle in numbers of snowshoe hares   /   Doyle, F.I.   Smith, J.N.M.
In: The Northern Goshawk : ecology and management / Edited by W.M. Block, M.L. Morrison, and M.H Reiser. - Los Angeles, Calif. : Cooper Ornithological Society, 1994, p. 122-129, ill.
(Studies in avian biology, no. 16)
(Kluane Boreal Forest Ecosystem Project contribution, no. 45)
References.
Paper in the Proceedings of a Symposium of the Cooper Ornithological Society, 14-15 April 1993, held in Sacramento, California.
ASTIS record 54183.
Languages: English
Libraries: QMM

We studied the abundance, diet, and migratory status of Northern Goshawks (Accipiter gentilis) at Kluane, southwest Yukon, Canada, from 1987 to 1993. This period spanned a local increase, peak, and decline in numbers of snowshoe hares (Leptus americanus). Goshawk sightings increased from 1988 to 1991, the year after hares reached peak densities, and about 40 pairs of goshawks occupied the 400 km² study area in 1990. As hare numbers fell, goshawk numbers dropped, birds became more nomadic, and their mortality increased within the study area. Goshawks nested mainly in mature but small spruce trees (Picea glauca). In the breeding season, male goshawks preyed heavily on hares, arctic ground squirrels (Spermophilus parryi), red squirrels (Tamiasciurus hudsonicus), and took some Spruce Grouse (Dendragapus canadensis) and Willow Ptarmigan (Lagopus lagopus). Hares made up 56% of the biomass of prey killed from 1989 to 1991. No successful breeding by goshawks was noted in 1992, after hare numbers declined to low levels. Data from mortality-sensing radio transmitters fitted to hares showed that goshawks accounted for about 10% (summer) to 17% (winter) of mortalities of radio-collared hares from fall 1988 to spring 1993. The number of breeding attempts located and the reproductive success of breeding pairs increased with hare densities. Pairs breeding at the hare peak fledged 2.8 young per nest. We suggest that this population of goshawks is resident year-round during periods of high hare numbers, because snowshoe hares are available as food in winter. In periods of low hare abundance, goshawks become more nomadic in spring, summer, and fall, and virtually disappear from the Kluane area in winter. (Au)


Early survival of juvenile snowshoe hares   /   O'Donoghue, M.
(Ecology, v. 75, no. 6, Sept. 1994, p.1582-1592, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 46)
References.
ASTIS record 53344.
Languages: English
Web: doi:10.2307/1939619
Libraries: ACU

Juvenile snowshoe hares (Lepus americanus) were radio-tagged at birth on one food addition grid and one control grid, to determine early juvenile survival, the effects of the food addition on survival, and proximate causes of mortality. Indices of survival were also estimated by live-trapping on these grids and on a replicate pair of grids. The overall 30-d survival rates of radio-tagged leverets were 0.46, 0.15, and 0.43 for the first, second, and third litters of the year, respectively. There were no differences between early juvenile survival on the food addition and control grids in any of the litter groups. The main proximate cause of juvenile mortality was predation by small mammalian predators, the most important being red squirrels and arctic ground squirrels. Seventy percent of early juvenile mortality occurred during the first 5 d after birth. Survival of littermates was not independent; litters tended to all live or die as a unit more often than expected by chance. Fifty-one percent of litters had no known survivors after 14 d of age. Individual survival rates were negatively related to litter size and positively related to body size at birth, and litter size was negatively correlated with body size. These correlations were most closely related to differences in life history traits among litters born at different times of the summer, rather than to trade-offs among traits within litter groups. (Au)


Herbaceous vegetation in the understorey of the boreal forest : does nutrient supply or snowshoe hare herbivory regulate species composition and abundance?   /   John, E.   Turkington, R.
(Journal of ecology, v. 83, no. 4, Aug. 1995, p. 581-590, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 47)
References.
ASTIS record 53345.
Languages: English
Web: doi:10.2307/2261626
Libraries: ACU

Summary: 1. The impact of nutrient addition and mammalian exclosures on the above-ground biomass and species composition of the understorey vegetation of the boreal forest were investigated in three field experiments. 2. Experiment 1 was run from 1990-92 during which time the major herbivore, the snowshoe hare, declined dramatically in numbers. It combined the addition of nutrients with the exclusion of herbivores in a 2 × 2 factorial design. Experiment 2 was run over an 8-week period in 1991, and tested the effects of exclosures on above-ground plant biomass at a range of snowshoe hare densities. Experiment 3 examined the effects of longer-term (6-year) exclosures, erected in 1987, on understorey species composition. 3. At natural densities, the impact of herbivores on vegetation is low compared with the effect of fertilizers. Fertilizer resulted in some species increasing in abundance and others decreasing. Where herbivores were at artificially high densities their impact was greater. There is a natural dynamic to the system as some species changed in abundance in control plots during the experiment. 4. The results suggest that both the composition and abundance of herbaceous vegetation in the boreal forest are determined more by the productivity of the site than the activities of mammalian herbivores, at least during the period of the experiments when hare numbers were declining naturally. (Au)


Predation on red squirrels during a snowshoe hare decline   /   Stuart-Smith, A.K.   Boutin, S.
(Canadian journal of zoology, v. 73, no. 4, Apr. 1995, p. 713-722, ill., maps)
(Kluane Boreal Forest Ecosystem Project contribution, no. 48)
(Kluane Red Squirrel Project contribution, no. 8)
References.
ASTIS record 53727.
Languages: English
Web: doi:10.1139/z95-083
Libraries: ACU

We examined the extent and impact of predation on red squirrels (Tamiasciurus hudsonicus) during a cyclic decline of snowshoe hares in the southwestern Yukon, Canada. We monitored survival of squirrels on three control grids and a predator exclosure from March 1991 through August 1993. On controls, adult survival during the breeding season decreased from 1991, when snowshoe hare populations were high, to 1992, when hare populations declined rapidly. Survival increased slightly in 1993, when hare and predator populations were very low. Similarly, adult survival during winter was lower in 1992-1993 than in 1991-1992. Adult survival on the exclosure remained similar in each breeding season but declined during winter 1992-1993. Adult survival was similar on the controls and the exclosure in each year except during winter 1991-1992 and the 1992 breeding season, when it was lower on the controls. There was no difference in juvenile survival between the controls and the exclosure. Despite the decrease in adult survival due to predation, there was no population decline on any of the control grids. We conclude that predation did not have a measurable impact on red squirrel densities at Kluane and that it is unlikely red squirrels show 10-year population cycles in conjunction with snowshoe hares. (Au)


A study of factors influencing a non-cyclic, island population of snowshoe hares   /   Zimmerling, T.   Krebs, C.J. [Supervisor]
Vancouver, B.C. : University of British Columbia, 1993.
x, 116 leaves : ill. ; 29 cm.
(Kluane Boreal Forest Ecosystem Project contribution, no. 49)
Thesis (M.Sc.) - University of British Columbia, Zoology Department, Vancouver, B.C., 1993.
References.
Appendices.
ASTIS record 33954.
Languages: English
Libraries: XYKLRS

In this study I examined potential causes of the observed demographic differences between Jacquot Island and mainland snowshoe hare (Lepus americanus) populations in the southwest Yukon. The population dynamics of hares on Jacquot Island have been observed to differ from the dynamics of a population undergoing a "10-year cycle," such as that on the adjacent mainland. Hare densities, predation rates, reproduction and juvenile survival were all monitored on both Jacquot Island and mainland study areas. Habitat on the study sites was also examined for cover and browse availability. Jacquot Island juveniles had survival rates 3-15 fold higher than mainland juveniles. The difference in leveret survival was attributed to the lack of small mammalian predators on the island. The Jacquot Island study grids had habitat with more dense understory than that of mainland areas. The density of cover at 10 cm above the ground was positively associated with juvenile survival, and may have also contributed to the observed differences in juvenile survival rates. Differences in predation pressure on adult hares were observed between the island and mainland. I examined the influence of stochastic predation on the Jacquot Island hare population through the use of simulation models. I found that stochastic predation alone could not account for the observed dynamics of the Jacquot Island population. Through the use of a simulation model I was also able to show that the Jacquot Island hare population would cycle in a manner similar to the mainland if it were exposed to predation which followed a Type II functional response and a 1-year-delayed density-dependent numerical response. This model produced cycles with a period of 9 years and a maximum hare density of 3.15 hares/ha. I concluded from this study that the observed differences in population dynamics between the mainland and Jacquot Island hare populations are caused in part by: 1) Differences in predation pressure between the mainlandand Jacquot Island, where Jacquot Island experiences stochastic variation in predation pressure from year to year, and the mainland experiences delayed density-dependent predation pressure. 2) Differences in the numbers of predators of juvenile hares, where Jacquot Island has only red squirrels as a small mammalian predator, while the mainland has red squirrels, Arctic ground squirrels and weasels. 3) Differences in hatitat, resulting in Jacquot Island having more dense "refuge habitat" than mainland areas. (Au)


Evaluation of capture-recapture estimators using a cyclic snowshoe hare population   /   Boulanger, J.   Krebs, C.J. [Supervisor]
Vancouver, B.C. : University of British Columbia, 1993.
xi, 183 p. : ill. ; 28 cm.
(Kluane Boreal Forest Ecosystem Project contribution, no. 50)
Thesis (M.Sc.) - University of British Columbia, Vancouver, B.C., 1993.
Appendix.
References.
Indexed from microfiche.
ASTIS record 60518.
Languages: English
Libraries: BVAU XYKLRS

Most theoretical capture-recapture estimation models have been introduced into applied field ecology in the last twenty years, but only a few of these models have been tested in field situations. The objective of this thesis was to evaluate capture-recapture estimators when applied to a cyclic snowshoe hare population in the Kluane Lake area in the Southern Yukon. The estimation models and model selection routine of program CAPTURE, and the Jolly-Seber open model were evaluated. Two independent approaches were used to evaluate estimators: 1) Island populations of known size were used to determine estimator biases and study factors that affect hare capture probabilities, and 2) An individual-based spatial Monte Carlo simulation model was used to evaluate estimator robustness to sample biases caused by a cyclic snowshoe hare population. Two islands were used for studies of estimator bias. Results from both islands suggest that the CAPTURE heterogeneity models Mh (jackknife, Mh (Chao), and Mth (time/heterogeneity) were approximately unbiased for the island population of hares. All other CAPTURE models displayed a negative bias. The program CAPTURE model selection routine picked models of different bias for each trapping period. Island studies of variation in hare capture probabilities documented a strong relationship between hare movement patterns and capture probabilities on an individual and population level. The strong contribution of sampling factors such as trap placement, and time of sampling in the variation of hare capture probabilities was also documented. A Monte Carlo model was used to determine estimator robustness to trap saturation with increasing hare densities, uneven trap spacing, and other sample biases typical of a cyclic snowshoe hare population. All models except the jackknife heterogeneity (Mh) estimator showed increasing negative bias with increasing simulated hare density. The jackknife estimator was robust to biases caused by trap saturation, and showed an acceptable coefficient of variation. The program CAPTURE model selection routine performed poorly when selecting estimation models of different bias for each simulated hare density. The results from the island studies and Monte Carlo simulation study were then compared to Kluane field data. Similar trends were evident in all the data sets. This study concludes that the jackknife estimator (Mh) is the most robust to sampling variations in a cyclic snowshoe hare population. The poor performance of the program CAPTURE model selection routine was documented. Recommendations for future research are given. (Au)


Reproduction, juvenile survival and movements of snowshoe hares at a cyclic population peak   /   O'Donoghue, M.   Krebs, C.J. [Supervisor]
Vancouver, B.C. : Universiy of British Columbia, 1991.
127 leaves : ill. ; 28 cm.
(Kluane Boreal Forest Ecosystem Project contribution, no. 51)
References.
Thesis (M.Sc.) - University of British Columbia, Vancouver, British Columbia, 1991.
ASTIS record 60574.
Languages: English
Libraries: BVAU OONL XYKLRS

Snowshoe hare (Lepus americanus) populations were provided with supplemental food on two study grids in the southwest Yukon to examine the effects of food on reproduction and juvenile growth. Timing of parturition, pregnancy rates, litter sizes, male breeding condition, and juvenile growth rates were measured on the food grids and on two control grids during two summers at a cyclic peak in hare numbers. The main effects of food addition were to increase hare densities 2.1- to 2.7-fold, to advance the timing of breeding by about a week in one year, and to increase the mean size of third litter 30% in one year relative to the controls. There were no significant differences in pregnancy rates, litter sizes in five of six litter groups, length of male breeding season, or juvenile growth rates between hare populations on the food and control grids. Third litter stillborn rates were higher, and third litter juveniles grew slightly more slowly on food grids relative to those on controls, possibly because of higher densities. This study suggests that food is not a proximate factor limiting hare reproduction and early juvenile growth at the observed peak hare densities. Juvenile snowshoe hares were radio-tagged at birth on one food addition grid and one control grid, to determine early juvenile survival rates, the effects of the food addition on these rates, and the proximate causes of mortality. Indices of survival were estimated by live-trapping on these grids, and on one additional set of grids. Thirty-day survival rates were 0.46, 0.15, and 0.43 for the first, second and third litters of the year, respectively. There were no differences between early juvenile survival on the food addition and control grids in any of the litter groups. The main proximate cause of juvenile mortality was predation by small mammalian predators, the most important being red squirrels and arctic ground squirrels. Seventy percent of early juvenile mortality occurred during the first 5 days after birth. Survival of littermates was not independent; litters tended to all live or die as a unit more often than expected by chance. Fifty-one percent of litters had no known survivors after 14 days of age. Individual survival rates were negatively related to litter size, positively related to body size at birth, and litter size was negatively correlated with body size, suggesting trade-offs as predicted by life history theory. The number of recruits per litter, and the probability of total litter failure, did not differ significantly over the observed range of litter sizes. The radio-tagged juveniles were also followed to examine pre-dispersal movements, maternal-juvenile interactions, and timing of natal dispersal. Hare litters stayed at their nest sites for an average of 2.7 days, after which each individual hare usually found a separate hiding place from its littermates. Juvenile hares ranged progressively farther from their nest sites as they grew, up to the age of 20 days. From 20 to 35 days of age, leverets stayed approximately 75 m from their nest sites, after which time their movements again increased. Observations at nest sites suggested that adult female hares nursed their litters only once per day, shortly after twilight. Some females aggressively defended their newborn litters before the juveniles left the nests. Natal dispersal of juvenile hares began shortly after weaning at 24-28 days of age. Many third litter juveniles were nursed for a longer period of at least 29-40 days. Juvenile males may disperse sooner and travel farther than females from their natal ranges. (Au)


Limitations of far infrared thermal imaging in locating birds   /   Boonstra, R.   Eadie, J.M.   Krebs, C.J.   Boutin, S.
(Journal of field ornithology, v. 66, no. 2, Spring 1995, p. 192-198, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 52 [44])
References.
Spanish abstract provided.
ASTIS record 53779.
Languages: English
Libraries: ACU

The utility of far infrared (FIR) thermal imaging devices to detect and census birds in the field was examined. A Thermovision 210 was used to survey individuals and/or nests of Great-horned Owls (Bubo virginianus), Pileated Woodpeckers (Dryocopus pileatus), Northern Flickers (Colaptes auratus), Barrow's Goldeneyes (Bucephala islandica), Buffleheads (Bucephala albeola), Mallards (Anas platyrhynchos), Green-winged Teal (Anas crecca), Lapland Longspurs (Calcarius lapponicus) and Pectoral Sandpipers (Erolia melanotos). Thermal imaging was successful in determining activity at nests of all four cavity-nesting species and in finding nests of Arctic tundra birds if their approximate location was known. FIR thermal imaging was not useful, however, in detecting the active, open nests of Mallards or Green-winged Teal, nor was it useful in locating resting waterfowl or Great-horned Owls. It was successful at locating Arctic tundra birds. These differences are largely attributable to variation among species in the insulative property of nests or feathers. It is concluded that FIR imaging will be of limited utility in censusing most avian populations, although it may provide a useful, abeit expensive tool, to assess nest occupancy of cavity- or burrow-nesting birds, or to determine the activity of birds in open habitats. (Au)


Costs of escalated territorial defence in red squirrels   /   Stuart-Smith, A.K.   Boutin, S.
(Canadian journal of zoology, v. 72, no. 6, June 1994, p.1162-1167, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 53)
(Kluane Red Squirrel Project contribution, no. 7)
References.
ASTIS record 53718.
Languages: English
Web: doi:10.1139/z94-156
Libraries: ACU

The costs of escalated territorial defence have not been well-documented, although in theoretical studies they are often assumed to be high. We manipulated territorial defence in red squirrels (Tamiasciurus hudsonicus) to assess the costs of territorial disputes in terms of energy, reproductive status, and predation. Feeders containing sunflower seeds were used to manipulate foraging behaviour and induce territorial disputes. Experimental squirrels displayed dramatically higher rates of territorial behaviours in response to feeders, and while there was no difference in survival between experimental and control squirrels, in 4 of the 17 disputes territory owners lost their territories. All 3 females that did so suffered reproductive costs. Territorial disputes were won by the heavier squirrels in all 12 cases where contestants were of different masses, but where the contestants were of similar masses (4 of 5 cases), territory owners were more likely to win. (Au)


Testing predator-prey theory by studying fluctuating populations of small mammals   /   Boutin, S.
(Wildlife research, v. 22, no. 1, 1995, p. 89-100, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 54 [!])
References.
ASTIS record 54162.
Languages: English
Web: doi:10.1071/WR9950089
Libraries: OON

Fluctuating populations of small mammals provide an excellent opportunity to study the functional and numerical responses of predators because of the wide range in prey density that occurs. I reinterpret data from six studies that have examined the role of predation in the population dynamics of voles in California, southern Sweden and western Finland, of snowshoe hares in northern Canada, and of house mice and rabbits in Australia. Most studies have measured functional responses by relying on changes in diet as reflected by scat or stomach contents. These methods are probably biased toward showing predator satiation. Contrary to previous conclusions I find that there is little evidence for non-linear (Type III) functional-response curves or predator satiation at high prey densities. Recent studies indicate that the functional and numerical responses of predators can be rapid and strong enough to initiate cyclic declines, dampen fluctuations, or even cause stable numbers. The exception to this appears to be the irruptions of mice and rabbits in Australia. I propose a general explanation for the role of predation whereby the effect of predation is largely dependent on the entire prey community. When potentially cyclic prey are a small component of the overall prey biomass, generalist predators are able to prevent fluctuations by strong functional or numerical responses. As the prey community becomes dominated by a few species that fluctuate, limit cycles predominate. Limit cycles turn into irruptive population dynamics when seasonal prey reproduction is eliminated because of extended periods of vegetation growth (vegetation flushes following drought). In the future we must test assumptions underlying the way we study predation by telemetric monitoring of prey mortality and by experimentally manipulating predation. (Au)


Behavioural differences between surviving and depredated juvenile red squirrels   /   Stuart-Smith, A.K.   Boutin, S.
(Écoscience, v. 2, no 1, 1995, p. 34-40, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 54 [79])
(Kluane Red Squirrel Project contribution, no. 9)
References.
ASTIS record 33416.
Languages: English
Web: doi:10.1080/11956860.1995.11682266
Libraries: ACU

Individuals killed by predation often are considered to be in poorer physical condition than those not killed, but little work has been done on behavioural differences between the two. We monitored the behaviour, movements and survival of 15 juvenile red squirrels (Tamiasciurus hudsonicus) from the first day of their emergence through late summer to determine behavioural characteristics associated with predation. Individuals which spent relatively less time vigilant, less time resting, and more time in exposed locations were more likely to be depredated. The distance moved by an individual during observation periods was not related to its survival, but individuals that spent relatively more time off their natal territory were more likely to be depredated. Adult red squirrels spent significantly less time in exposed places than juveniles, which may relate to the lower depradation rates experienced by adults. (Au)


Comparison of capture - recapture estimators of snowshoe hare populations   /   Boulanger, J.   Krebs, C.J.
(Canadian journal of zoology, v. 72, no. 10, Oct. 1994, p.1800-1807, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 55)
References.
ASTIS record 53721.
Languages: English
Web: doi:10.1139/z94-244
Libraries: ACU

We used two island populations of snowshoe hares (Lepus americanus) in the Kluane Lake area of the Yukon Territory of Canada to evaluate capture-recapture estimators. These islands were intensively sampled, allowing us to enumerate the actual population size. Population size estimates were calculated using the programs CAPTURE and JOLLY, and estimators were compared for bias characteristics. Results from both islands suggest that the CAPTURE heterogeneity models Mh (jackknife), Mh (Chao), and Mth (time-heterogeneity) and the Jolly-Seber model were approximately unbiased. All other CAPTURE models displayed a negative bias. The CAPTURE model selection routine picked estimation models of different biases for each trapping period, an undesirable result. We conclude that it is best to use one robust estimator such as the Mh (jackknife) with snowshoe hare data. (Au)


Efficacy of invermectin against nematodes infecting field populations of snowshoe hares (Lepus americanus) in Yukon, Canada   /   Sovell, J.R.   Holmes, J.C.
(Journal of wildlife diseases, v. 32, no. 1, Apr. 1996, p. 23-30, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 56)
References.
ASTIS record 54164.
Languages: English
Web: doi:10.7589/0090-3558-32.1.23
Libraries: ACU AEEN

From July 1990 to February 1991, nematode numbers in free-ranging snowshoe hares (Lepus americanus) at Kluane Lake, southwestern Yukon, Canada, were manipulated by subcutaneous injection (0.4 mg/kg) of ivermectin. Three field experiments were conducted to determine the degree of helminth loss associated with a single administration of ivermectin; the length of time that ivermectin was effective in reducing worm numbers; and the effect of repeated ivermectin administration in reducing worm numbers. Numbers of the nematodes, Protostrongylus boughtoni and Nematodirus triangularis were reduced by approximately 80% 2 wk after treatment with a single dose of ivermectin, and were still significantly lower than controls at 4 wk. However, beyond 2 wk, ivermectin did not affect the rate of acquisition of new worms of either species. All treated groups contained one or more hares in which numbers of P. boughtoni and N. triangularis were not reduced. In addition, ivermectin had no effect on numbers of Trichuris leporis or Passalurus sp. Overall, ivermectin was not as effective against the nematodes of free-ranging hares as has been reported for nematodes of domestic and laboratory animals. (Au)


Herbivore-plant-soil interactions in the boreal forest : selective winter feeding by spruce grouse   /   Mueller, F.P.   Sinclair, T. [Supervisor]
Vancouver, B.C. : University of British Columbia, 1993.
vii, 123 p. : ill., 2 maps ; 28 cm.
(Kluane Boreal Forest Ecosystem Project contribution, no. 57)
Thesis (M.Sc.) - University of British Columbia, Vancouver, B.C., 1993.
References.
Appendix.
ASTIS record 33955.
Languages: English
Libraries: XYKLRS

This thesis examines the unusual winter forage selection of spruce grouse (Dendragapus canadensis) in the Yukon. The winter diet of spruce grouse consists entirely of conifer needles. Spruce grouse feed selectively on individual trees (feeding trees) of a single species, white spruce (Picea glauca), leaving adjacent trees of similar size and age uneaten. These feeding trees are used throughout the winter and some are used repeatedly for several years. Accumulations of droppings on the ground and defoliated branches indicate preferred trees. Between 0.3 to 5.0 kg dry weight of spruce grouse faeces accumulate annually under feeding trees and between 25 to 90% (mean 40%) of the needles on preferred trees are removed by feeding grouse. Why do spruce grouse feed so selectively? Chapter 2 describes the role of foliar chemistry in the selection of winter forage by spruce grouse. During feeding trials, captive spruce grouse had a marked preference for needles from feeding trees over control trees. Chemical analyses of needles also support the hypothesis that needle chemistry accounts for the winter forage selection of spruce grouse. Concentrations of two monoterpene antifeedants, camphor and bornyl acetate, and the ratio of resin to nitrogen, were inversely related to grouse forage preferences and may explain the selection by spruce grouse of individual trees for winter feeding. Feeding trees are exposed during winter to recurring high levels of herbivory by spruce grouse. This herbivory may affect growth rate, architecture, reproductive output, and chemical defence of selected trees (Chapter 3). Feeding trees have higher lateral (twig) growth rates, longer needles, and longer, more highly branched limbs and more rounded crowns than control trees. Also, cone production is significantly lower in feeding trees than in adjacent control trees. The relatively high growth rates, the low reproductive output, and the low secondary chemical content of feeding trees suggests a within-tree trade-off in allocation of limited carbon resources. Large amounts of spruce grouse faeces accumulate annually under feeding trees. Decomposition of these faeces is rapid relative to spruce litter. In the nutrient limited boreal forest, spruce grouse faecal inputs under feeding trees may locally increase soil nutrient availability and nutrient cycling rates (Chapter 4). The nitrogen content of grouse faeces may account for the relatively high growth rates of feeding trees and may lead to the higher forage quality of feeding trees compared with control trees. Experimental defoliation and fertilization of white spruce trees suggests that the observed differences between feeding trees and adjacent control trees result, in part, from the effects of selective feeding by spruce grouse. The growth rates of experimentally ferti1ized trees increased significantly over control tree growth rates suggesting faecal input is critical to regrowth. The growth rates of clipped trees did not change in response to simulated grouse herbivory. The combined effects of defoliation and nutrient return by spruce grouse may lead to regrowth that is more palatable than forage on uneaten plants. Spruce grouse feeding may result in patches of highly palatable forage that attract further feeding, generating a feeding-regrowth feedback loop (Chapter 5). Positive effects on forage palatability and quantity may account for the unusual and prolonged use by spruce grouse of individual trees for winter feeding. Spruce grouse may be farming their food plants. (Au)


Bigamy in Red-tailed Hawks in southwestern Yukon   /   Doyle, F.I.
(The Journal of raptor research, v. 30, no. 1, Mar. 1996, p. 38-40)
(Kluane Boreal Forest Ecosystem Project contribution, no. 60)
References.
Resume also in Spanish.
This paper is a short communication.
ASTIS record 54030.
Languages: English
Libraries: SSU

Polygyny is well documented in some raptor species ... and is usually associated with an abundant food supply .... In red-tailed hawks (Buteo jamaicensis), only two cases of polygyny have been reported .... In both cases two females shared the same mate and nest, but no information on food availability was available. Here I describe three incidents of bigamy in a red-tailed hawk population. In these incidents a male was mated with two females at different nests, during years of declining prey abundance. ... The raptor community at Kluane Lake in the southwestern Yukon has been studied since 1986, as part of a larger project examining the boreal forest ecosystem .... A total of 380 raptor territories of nine species, including 75 red-tailed hawk territories, have been closely monitored. The ability to identify individuals by their plumage patterns helped me to realize that bigamy was occurring in this red-tailed hawk population. ... Another characteristic helpful in identifying possible cases of bigamy was the nearest-neighbor nest distance. Bigamous nests were much closer together (750-800 m) than were monogamous nests (1400-3500 m; Welch's approximate t-test, P=0.0000) within years and over the entire study period. In 1992, two territories contained males paired with two females at different nests. At these sites, individually distinguishable plumage patterns were particularly useful. In the first territory, the nests were 750 m apart, and in sight of each other. ... The other two cases of bigamy were more circumstantial. In the second territory in 1992, the two nests were also 750 m apart. ... [in previous studies] bigamy was associated with abundant food supply. This association with an abundant rood supply was not obvious in our study area. An apparent peak in food availability occurred at the height of the snowshoe hare (Lepus americanus) cycle in 1989-90 .... However, bigamy in red-tailed hawks was only observed in 1991 and 1992. Variations in fledging success may have been the trigger for bigamy in our population. During the period of greatest food supply at the peak or the hare cycle in 1989 and 1990, a peak in fledging success occurred with a mean of 1.75 (SD=1.12) chicks fledged from 20 pairs. At the hare low in 1991 and 1992, only 0.76 (SD=0.88) chicks were fledged per pair. This 1989-90 high in fledging success may have caused an increase in the number or birds in breeding condition over the next few years. Therefore, the incidence of bigamy in 1991 and 1992 may have been due to unpaired females joining an established pair rather than not breeding at all. Bigamy described here may also be a feature of the northern location. The birds have a short breeding season after migration. Nest building and egg laying begin almost immediately after arrival in mid-April, with a median egg laying date of 28 April. The birds, therefore, have little time to assess the quality of the territory or their mate. A female could mate with a male who already had a mate, either by accident or before the quality of the territory is known. Whatever the reason for bigamy, 67% of the bigamous red-tailed hawk nests failed to fledge young. All three territories failed to fledge young from both nests, and in one case, both nests failed. These rates are similar to the monogamous pairs' breeding success where 55% of 22 nests failed to fledge any young in the low of the hare population cycle in 1991 and 1992. Bigamy in this red-tailed hawk population may be successful only with an abundant food supply. (Au)


Robustness of capture-recapture estimators to sample biases in a cyclic snowshoe hare population   /   Boulanger, J.G.   Krebs, C.J.
(Journal of applied ecology, v. 33, no. 3, June 1996, p. 530-542, ill., 1 map)
(Kluane Boreal Forest Ecosystem Project contribution, no. 61)
Appendices.
References.
ASTIS record 53346.
Languages: English
Web: doi:10.2307/2404982
Libraries: ACU

Summary: 1. A Monte Carlo simulation model was used to determine estimator robustness to trap saturation and other sample biases typical of a cyclic snowshoe hare population. 2. Field studies showed that hare capture probability varied directly with the amount of nightly movement made by an individual. This relationship was simulated by using an individual-based model of individual hare movement and the trapping process. 3. All estimation models in program CAPTURE except the jackknife heterogeneity (Mh) estimator showed increasing negative bias with increasing hare abundance in computer simulations. The jackknife estimator was robust to biases caused by trap saturation, and showed an acceptable coefficient of variation. 4. The program CAPTURE model selection routine performed poorly by selecting estimation models of different bias for each simulated hare abundance. 5. We conclude that for closed populations the jackknife estimator (Mh) is the most robust to sampling variation in a cyclic snowshoe hare population. These results suggest that it is optimal to use one model rather than change models for populations which exhibit large changes in abundance. (Au)


Evidence for bottom-up effects in the boreal forest : do passerine birds respond to large-scale experimental fertilization?   /   Folkard, N.F.G.   Smith, J.N.M.
(Canadian journal of zoology, v. 73, no. 12, Dec. 1995, p.2231-2237, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 62)
References.
ASTIS record 53728.
Languages: English
Web: doi:10.1139/z95-264
Libraries: ACU

Boreal plant communities are strongly nutrient limited, and the animals of the boreal forest may therefore experience bottom-up nutrient limitation. We conducted a 5-year experimental study of the impact of aerial nitrogen fertilization on birds of the boreal forest near Kluane Lake, southwestern Yukon, to test for such bottom-up effects. Specifically, we tested if avian abundance and species richness increased after fertilization. Variable circular-plot point counts were made to estimate bird numbers and species richness each summer from 1988 to 1992. Fertilization had no effect on abundance for the first two summers, but total abundances of the seven commonest passerine bird species increased by an average of 46% over the final 3 years. Fertilization had no effect on bird species richness. Population densities and species richness were both low at Kluane compared with patterns seen in temperate forest. Yellow-rumped warblers (Dendroica coronata), dark-eyed juncos (Junco hyemalis), and Swainson's thrushes (Catharus ustulatus) dominated the passerine community at Kluane. There was only moderate spatial and temporal variation in songbird numbers on control plots over the 5-year study period. (Au)


Population limitation in arctic ground squirrels : effects of food and predation   /   Hubbs, A.H.   Boonstra, R.
(Journal of animal ecology, v. 66, no. 4, July 1997, p. 527-541)
(Kluane Boreal Forest Ecosystem Project contribution, no. 63)
References.
ASTIS record 43226.
Languages: English
Web: doi:10.2307/5947
Libraries: ACU

Summary: 1. We examined the relative importance of food and predators in limiting Arctic ground squirrel (Spermophilus parryii plesius Richardson) populations in the boreal forest of the southwestern Yukon during the peak and early decline of a snowshoe hare cycle (Lepus americanus Erxleben). 2. Squirrels were live-trapped from 1990 to 1992 on two control grids and three experimental treatments (food addition, mammalian and avian predator exclosure, and food addition plus mammalian predator exclosure). Adult squirrels were radio-collared on all areas in 1992. 3. Food addition increased densities 3-8 times, generally increased reproductive traits (increased proportion of females lactating, doubled recruited litter sizes, resulted in earlier emergence of juveniles), increased immigration rates (but only in 1992), resulted in heavier females though not males at emergence in spring, and resulted in more rapid growth rates of juvenile males, but not of juvenile females. It had no effect on active season or overwinter survival rates. 4. Exclusion of predators had virtually no effect on any demographic variable measured, except for population densities in 1991 when they were approximately double those of the control populations. 5. Food addition plus exclusion of mammalian predators resulted in demographic changes that were comparable to those of food addition alone. 6. Thus, it appeared that food, not predators, limited ground squirrel populations at this stage of the hare cycle. However, independent of experimental treatment, active season survival of adult squirrels declined markedly from 1990 (high hare numbers) to 1992 (low hare numbers). Most of the radiocollared squirrels disappearing in 1992 were killed by predators and this was coincident with high densities of predators. In the predator exclosures, all predation mortalities resulted from avian predators which we could not exclude. 7. We conclude that both food and predators interact to limit Arctic ground squirrel populations during the peak and early decline of the hare cycle. (Au)


Northern Hawk-Owls in the Nearctic boreal forest : prey selection and population consequences of multiple prey cycles   /   Rohner, C.   Smith, J.N.M.   Stroman, J.   Joyce, M.   Doyle, F.I.   Boonstra, R.
(The Condor (Los Angeles, Calif.), v. 97, no. 1, Feb. 1995, p. 208-220, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 64)
Appendix.
References.
ASTIS record 53783.
Languages: English
Libraries: ACU

We studied hawk-owls in the southwestern Yukon, Canada, from 1987-1993. Most information on hawk-owls originates from studies in Europe, and very little is known about the subspecies Surnia ulula caparoch in North America. The boreal forest communities in the two continents differ remarkably in the composition of cyclic herbivore populations. Fennoscandia is dominated by 3-4 year microtine cycles, whereas northern Canada and Alaska experience a 10-year cycle in snowshoe hare numbers, with voles fluctuating at lower levels. We studied the diets of nine nesting pairs by pellet analysis, and we observed prey deliveries at five nests. The proportion of voles in the diets was lower than reported from Fennoscandia, and snowshoe hares made up 40-50% during the peak of the hare cycle. Estimates of prey densities by live-trapping revealed that hawk-owls strongly prefer voles over snowshoe hares and squirrels. Among voles, Microtus were preferred and Clethrionomys were avoided. Hawk-owls showed, however, a functional response not only to voles but also to juvenile hares, and they may be critically dependent on larger prey during certain nesting stages when vole abundance is moderate or low. Breeding densities and winter observations changed concurrently over years of different prey abundance. Prey selection translated into population consequences: hawk-owls did not respond numerically to Clethrionomys outbreaks, but to the combined densities of Microtus and snowshoe hares. We conclude that the Northern Hawk-Owl is less of a vole specialist and more affected by the prey composition in specific systems than commonly assumed, and we discuss this pattern from an evolutionary perspective. (Au)


First-year survival of Great Horned Owls during a peak and decline of the snowshoe hare cycle   /   Rohner, C.   Hunter, D.B.
(Canadian journal of zoology, v. 74, no. 6, June 1996, p.1092-1097, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 65)
References.
ASTIS record 53301.
Languages: English
Web: doi:10.1139/z96-121
Libraries: ACU

Most bird species have low survival rates in their first year of life, and the highest losses occur when juveniles become independent and disperse. Young great horned owls (Bubo virginianus), monitored by telemetry in the southwestern Yukon, Canada, survived well during the peak of the population cycle of snowshoe hares (Lepus americanus). Subsequently, juvenile survival collapsed parallel to the decline in hare densities. The proportion of starving owls did not increase, but there was a significant increase in mortalities involving parasitism and predation, probably as an interaction with food shortage. The mortality rates of juvenile great horned owls peaked before, not during, dispersal. We propose that extended parental care makes the postfledging stage safe during optimal conditions, but that the relatively slow development during this stage incurs the cost of increased susceptibility to disease and other mortality factors under environmental stress. (Au)


Bald Eagle, Haliaeetus leucocephalus, and Northern Goshawk, Accipiter gentilis, nests apparently preyed upon by a wolverine(s), Gulo gulo, in the southwestern Yukon Territory   /   Doyle, F.I.
(Canadian field-naturalist, v.109, no. 1, Jan.-Mar. 1995, p. 115-116)
(Kluane Boreal Forest Ecosystem Project contribution, no. 66)
References.
ASTIS record 53210.
Languages: English
Libraries: ACU

I present evidence of apparent Wolverine (Gulo gulo) predation on one Bald Eagle (Haliaeetus leucocephalus, and one Northern Goshawk (Accipiter gentilis) nest in Kluane Lake area of the Yukon Territory. (Au)


Does reproductive synchrony affect juvenile survival rates of northern mammals?   /   O'Donoghue, M.   Boutin, S.
(Oikos, v. 74, no. 1, Oct. 1995, p. 115-121, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 67)
(Kluane Red Squirrel Project contribution, no. 10)
References.
ASTIS record 53770.
Languages: English
Web: doi:10.2307/3545680
Libraries: ACU

Predator swamping is often cited as an adaptive function of reproductive synchrony. We measured juvenile survival rates of two boreal mammals, snowshoe hares (Lepus americanus) and red squirrels (Tamiasciurus hudsonicus), and evaluated the effect of timing of birth relative to the population mean on subsequent survival. Reproduction of hares was highly synchronous. Juvenile hares were born in three distinct litter groups per summer, and they suffered high early mortality due to predation. Juveniles born closest to the population mean had higher survival than those born later for two of the three litter groups. The timing of red squirrel litters was more variable, and squirrels only had one litter per summer. The juvenile survival rates of squirrels were high relative to those of hares. Degree of synchrony had no effect on survival rates of juvenile squirrels to emergence or from emergence to weaning. We suggest that predation selects for tighter reproductive synchrony of snowshoe hares, at least while they are at peak densities, but that it has little effect on the timing of red squirrel reproduction. (Au)


Population changes of the vertebrate community during a snowshoe hare cycle in Canada's boreal forest   /   Boutin, S.   Krebs, C.J.   Boonstra, R.   Dale, M.R.T.   Hannon, S.J.   Martin, K.   Sinclair, A.R.E.   Smith, J.N.M.   Turkington, R.   Blower, M.   Byrom, A.   Doyle, F.I.   Doyle, C.   Hik, D.   Hofer, L.   Hubbs, A.   Karels, T.   Murray, D.L.   Nams, V.   O'Donoghue, M.   Rohner, C.   Schweiger, S.
(Oikos, v. 74, no. 1, Oct. 1995, p. 69-80, ill., 1 map)
(Kluane Boreal Forest Ecosystem Project contribution, no. 68)
(Kluane Red Squirrel Project contribution, no. 11)
References.
ASTIS record 39829.
Languages: English
Web: doi:10.2307/3545676
Libraries: ACU

We measured the density changes of 22 species of vertebrates during a snowshoe hare cycle in northern Canada. Hares were the dominant herbivore in the system and changes in their numbers were correlated with changes in numbers of arctic ground squirrel, spruce grouse, ptarmigan, lynx, coyote, great horned owl, goshawk, raven and hawk owl. Hare numbers were not correlated with numbers of red-backed vole which showed peaks during the low, increase, and early decline phases of the hare cycle. Hawk owls were the only predator whose numbers correlated with changes in red-backed voles while boreal owls and weasels were correlated with densities of Microtus. Red squirrel, American kestrel, red-tailed hawk, northern harrier, wolverine, magpie and gray jay showed no correlation with hare or vole numbers. We conclude that species in the boreal forest of Canada do not exhibit the strong synchrony found between voles and other members of the verterbrate community in northern Fennoscandia. We discuss some of the possible reasons for these differences. (Au)


Brood size manipulations in Great Horned Owls "Bubo virginianus" : are predators food limited at the peak of prey cycles?   /   Rohner, C.   Smith, J.N.M.
(Ibis, v.138, no. 2, Apr. 1996, p. 236-242, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 69)
Appendix.
References.
ASTIS record 53780.
Languages: English
Web: doi:10.1111/j.1474-919X.1996.tb04334.x
Libraries: ACU

The reproduction of raptors strongly depends on food resources. It is unclear whether predators experience superabundant food during cyclic peaks of prey populations. In order to test this hypothesis, four pairs of Great Horned Owls "Bubo virginianus" with two young were subjected to brood size manipulations during high densities of cyclic Snowshoe Hare, Lepus americanus, populations in southwestern Yukon, Canada. Broods older than 35 days were temporarily enlarged by one, and then by two, young. No effects were observed when one owlet was added, but the addition of two young resulted in significant weight losses in manipulated broods. Females with enlarged broods moved farther from their nest sites at night, presumably reflecting increased hunting effort, and also spent less time near the nest during the day. Food additions to enlarged broods returned the parental behaviour to normal. We conclude that these large predators did not experience superabundant food at this stage of the breeding season during a peak in cyclic prey. (Au)


The numerical response of Great Horned Owls to the snowshoe hare cycle : consequences of non-territorial 'floaters' on demography   /   Rohner, C.
(Journal of animal ecology, v. 65, no. 3, May 1996, p. 359-370, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 70)
References.
ASTIS record 53273.
Languages: English
Web: doi:10.2307/5882
Libraries: ACU

1. The numerical response of great horned owls (Bubo virginianus Gmelin) to the 10-year population cycle of snowshoe hares (Lepus americanus Erxleben) in the boreal forest was examined during 1988-93 in the south-western Yukon, Canada. Demographic parameters were estimated based on censuses (territorial pairs), nest visits (productivity), and radio-telemetry (survival, emigration, and integration of young birds into the population). 2. Hares rose to peak densities in 1990, and almost all resident owl pairs bred and raised large broods during years of increasing and highest prey abundance. In 1991, the first year of hare decline, all breeding parameters including post-fledging survival were reduced, and recruitment in autumn was very low. In 1992 and 1993, reproduction was completely suppressed. 3. Survival of young owls in their first 2 years of life was high during the peak of the hare cycle, and a large number of non-territorial 'floaters' were present. These birds were silent, and moved more than territorial owls. Their ranges overlapped broadly with defended territories, and floaters were affected by the hare decline before territory holders. 4. Most ecological studies on birds are based on the territorial fraction of a population. The results of this study show how a large proportion of secretive floaters can delay the detection of population declines in traditional censuses of territorial birds, and can lead to serious underestimates of the impacts of predation. (Au)


Great Horned Owls and snowshoe hares : what causes the time lag in the numerical response of predators to cyclic prey?   /   Rohner, C.
(Oikos, v. 74, no. 1, Oct. 1995, p. 61-68, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 71)
References.
ASTIS record 53771.
Languages: English
Web: doi:10.2307/3545675
Libraries: ACU

Predator populations often decline with a time lag after the peak of prey cycles. Theoretical models of predator-prey interactions predict that this delay is caused by a higher rate of population growth in prey, which leaves predators with super-abundant food after the peak and buffers their decline. This situation is met when predator populations have a lower innate capacity for increase than their prey or when the increase is inhibited because of territorial behaviour. Here, I refer to this hypothesis as 'single prey hypothesis' (SPH) in contrast to the 'multiple prey hypothesis' (MPH), which predicts that the delayed decline is caused by high availability of other prey species. Results on population growth rates of great horned owls showed that the predictions of SPH were met, although the predicted difference was small when floaters were taken into account or social exclusion from breeding was removed in a population model. In their diet, great horned owls relied to a large degree on the main cyclic prey (snowshoe hares), and thus the results were not in agreement with the MPH. Inverse density-dependent growth rates in the territorial population, density-dependent accumulation of floaters, and replacements of territorial vacancies were consistent with the hypothesis that social behaviour limited the number of owl territories. Reproduction of resident owls was immediately affected by the prey decline, indicating that there was no buffering effect of super-abundant food. Therefore, neither MPH nor SPH were satisfactory explanations, and I propose a mechanism based on individual behaviour to explain delayed numerical responses: territorial predators monopolize a disproportionately large amount of resources for reproduction during the increase and peak of the cycle, and are then buffered against prey declines by adjusting their breeding activities. Non-territorial floaters have lower access to resources and their numbers are affected more immediately by declining prey. (Au)


Space use in a population of least chipmunks in the southwest Yukon   /   Glennie, L.C.   Krebs, C.J. [Supervisor]
Vancouver, B.C. : University of British Columbia, 1988.
ix, 77 p. : ill., maps ; 28 cm.
(ProQuest Dissertations & Theses publication, no. ML47059)
(Kluane Boreal Forest Ecosystem Project contribution, no. 72)
ISBN 0-315-47059-3
Thesis (M.Sc.) - University of British Columbia, Vancouver, B.C., 1988.
Appendix.
References.
Indexed from microfiche.
ASTIS record 60537.
Languages: English
Libraries: BVAU XYKLRS

This thesis describes an investigation of space use in least chipmunks at Kluane Lake, in the southwest Yukon. I examined demography, home range and habitat use patterns in the population. Based on live-trapping data from two grids over two summers, mean number of animals on the study area was 22.6/grid, similar to chipmunk numbers measured there over the previous four years. The population was lower than is generally found in the same species further south, although year-to-year stability was typical. Chipmunks preferred open forest and shrub-land to closed-canopy forest, which is also typical of the genus. Home range sizes measured using telemetry averaged 4.86 ha, higher than in any previously published study of the genus. I examined the relationship between social spacing and space use. Home range overlap averaged 93.4%; chipmunks do not appear to defend exclusive core areas. Provoked interactions among neighbours suggested that social dominance was based on age, weight, and breeding condition, rather than ownership of space. Although provoked interactions were generally aggressive, the telemetry data suggest that such behaviour was artifactual. Comparing the encounter frequency of radio-collared animals to that generated by a random model showed that chipmunks avoided encounters, except when harvesting seasonally abundant food. Grid-trapping did not increase food or cover availability enough to affect home range size. There was evidence that the presence of traps affected use distribution, but not enough to invalidate trap-based home range estimates. Comparison of trap and telemetry based estimates of home range size yielded no significant differences. (Au)


The relative effect of clipping, neighbours, and fertilization on the population dynamics of Lupinus arcticus (family Fabaceae)   /   Graham, S.A.   Turkington, R. [Supervisor]
Vancouver, B.C. : University of British Columbia, 1994.
xiii, 134 leaves : ill. ; 28 cm.
(Kluane Boreal Forest Ecosystem Project contribution, no. 73)
Thesis (M.Sc.) - University of British Columbia, 1994.
Appendix.
References.
Indexed from microfiche.
ASTIS record 60528.
Languages: English
Libraries: BVAU XYKLRS

A demographic study was conducted in 1991 and 1992 on replicated field populations of Lupinus arcticus, near Kluane Lake, Yukon. The relative effects of herbivory, neighbours, and soil fertility level were assessed using a factorial experiment of +/- clipping, +/- neighbour removal, and +/- fertilizer (NPK). The main population experiment monitored the dynamics of leaves, however, data on reproduction, survival, and size were also collected from the permanent quadrants. Clipping reduced leaf cohort survivorship, total leaf density, and the incidence of disease on leaves, but resulted in an increased standing crop of leaves. Removing neighbours increased the percent cover of L. arcticus and decreased total leaf mortality. Fertilizing increased the incidence of disease on leaves, and reduces the standing crop of leaves. Significant three-way interactions between treatments affected the plasticity of petiole length distributions for L. arcticus. Between-year differences in the responses to the treatments were also detected, particularly for reproductive investment and output in L. arcticus. Although a number of significant responses to treatments were detected, nevertheless, the overall tendency was for a lack of response, especially pertaining to leaf population dynamics. This low response to the treatments imposed is consistent with Grime's (1979) arguments that plants growing in low productivity, infrequently disturbed habitats (i.e. stressful sensu Grime 1979) should show little response to short-term changes in local environmental conditions. (Au)


Predator versus predator : in the Yukon, when the going gets tough, the tough get eaten   /   O'Donoghue, M.   Hofer, E.   Doyle, F.I.
(Natural history, v.104, no. 3, Mar. 1995, p. 6-9, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 74)
ASTIS record 53370.
Languages: English
Libraries: ACU

As the coyote trotted across the gravel road in front of us, we slowed our car to admire its tawny coat and graceful gait. We frequently observed coyotes as we went about our work, since they are fond of using roadways to expedite their travel and hunt voles. But something was different this time. Instead of the coyote's usual cautious attention to human intruders and their vehicles, this animal kept its gaze intently fixed straight ahead. Halfway across the road, the coyote abruptly broke into a full-bore charge that ended in two long bounds and a flurry of fur and flying paws. We slammed on the brakes and backed up the car. The coyote ran off into the forest, leaving behind the body of a dead lynx. Careful examination revealed that the coyote had broken the neck of its victim, a young animal weighing only about fifteen pounds. Even so, the lynx was at least two-thirds the size of the coyote and quite capable of putting up a good fight. Was this incident a fluke or an example of a regular, although seldom observed, predatory behavior? For the past eight years, we have worked in the southwest Yukon Territory as a part of the Kluane Boreal Forest Ecosystem Project, a collaborative research effort by biologists from three Canadian universities. The broad aim of these studies is to gain an understanding about how the food web in the extensive coniferous forests of the north works, that is, what determines how many predators and how many herbivores there are and of what species. The studies have focused on one of the most conspicuous features of northern ecology, the ten-year population cycle of the snowshoe hare, a cycle that we were to learn can drastically affect the interactions among the hare's predators. Along with red squirrels and voles, snowshoe hares are the most abundant plant-eating mammals in the boreal forests of Canada and Alaska. They are also the staple food of many predatory mammals and birds, including lynxes, coyotes, great horned owls, and goshawks. Throughout this region, the number of hares fluctuates drastically over time, with populations reaching peak densities every eight to eleven years. These high points are followed by crashes in which hare numbers may decline to one three-hundredths of their highest levels. We know from fur company records that this cycle has been going on for as long as records have been kept, but there is still no widely accepted explanation for why it happens. Both predator prey and plant herbivore interactions have been proposed as the principal mechanisms generating the cycle, and part of the research objective of the Kluane Project is to untangle these hypotheses. ... Two other studies of lynxes in northern Canada have also concluded that when times are rough, predators sometimes feed on their fellow carnivores. ... Trappers' observations and native oral tradition support the notion that cannibalism and predation among predators often occurs when hares are scarce. ... Over the past eight years, we have also documented forty-five cases of raptors killing other birds of prey. ... This kind of predation may have far-reaching effects on how natural communities function. When lynx turns on lynx, for example, does this take pressure off the depleted hare population and slow its decline? And what is the effect on other prey in the boreal forest, such as squirrels and voles? With all these unanswered questions, we are certain that we will be testing our ideas about the boreal ecosystem for many seasons to come. We have learned one thing, though: the better we understand even a relatively simple food web, like that in the northern forests, the more we realize how complex it really is. (Au)


Feeding avoidance of balsam poplar by snowshoe hares is related to abundance of buds   /   Sinclair, A.R.E.   Williams, D.E.   Andersen, R.J.   Pain, J.
(Écoscience, v. 3, no 2, 1996, p. 223-225, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 75)
References.
ASTIS record 52704.
Languages: English
Web: doi:10.1080/11956860.1996.11682335
Libraries: ACU

In boreal forests of North America balsam poplar (Populus balsamifera) stems contain several chemicals distasteful to snowshoe hares. Some chemicals occur in internodes, others in buds. We examined whether an antifeedant chemical in buds (2,4,6-trihydroxydihydrochalcone) also inhibited hares from feeding on internodes. This chemical was painted onto buds of palatable willow (Salix lucida) twigs which were presented to hares in cafeteria trials. Hares avoided twigs with painted buds and the degree of aversion was related to the abundance of painted buds. Although the number of buds per unit mass of balsam poplar stems declined from one to five years old, the remaining buds were sufficient to induce a feeding deterrence. (Au)


The impact of predator-induced stress on the snowshoe hare cycle   /   Boonstra, R.   Hik, D.   Singleton, G.R.   Tinnikov, A.
(Ecological monographs, v. 68, no. 3, Aug. 1998, p. 371-394, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 76)
References.
ASTIS record 47446.
Languages: English
Web: doi:10.2307/2657244
Libraries: ACU

The sublethal effects of high predation risk on both prey behavior and physiology may have long-term consequences for prey population dynamics. We tested the hypothesis that snowshoe hares during the population decline are chronically stressed because of high predation risk whereas those during the population low are not, and that this has negative effects on both their physiology and demography. Snowshoe hares exhibit 10-yr population cycles; during declines, virtually every hare that dies is killed by a predator. We assessed the physiological responsiveness of the stress axis and of energy mobilization by subjecting hares during the population decline and low to a hormonal-challenge protocol. We monitored the population demography through live-trapping and assessed reproduction through a maternal-cage technique. During the 1990s' decline in the Yukon, Canada, hares were chronically stressed - as indicated by higher levels of free cortisol, reduced maximum corticosteroid-binding capacity, reduced testosterone response, reduced index of body condition, reduced leucocyte counts, increased overwinter body-mass loss, and increased glucose mobilization, relative to hares during the population low. This evidence is consistent with the explanation that predation risk, not high hare density or poor nutritional condition, accounted for the chronic stress and for the marked deterioration of reproduction during the decline. Reproduction and indices of stress physiology did not improve until predation risk declined. These findings may also account for the lag in recovery of hare reproduction after predator densities have declined and thus may implicate the long-term consequences of predation risk on prey populations beyond the immediate effects of predators on prey behavior and physiology. (Au)


Population cycles in small mammals : the problem of explaining the low phase   /   Boonstra, R.   Krebs, C.J.   Stenseth, N.C.
(Ecology, v. 79, no. 5, July 1998, p.1479-1488, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 77)
References.
ASTIS record 47450.
Languages: English
Web: doi:10.2307/176770
Libraries: ACU

Cycles characterize the demography of many populations of microtine rodents and snowshoe hares. A phase of low numbers often follows the decline and introduces a lag that lengthens the cycle. This low can last 1-3 yr in microtines and 2-4 yr in hares. Understanding the low phase is critical in explaining population cycles. Two major classes of hypotheses try to account for the low phase. The first proposes that something may be "wrong" with the extrinsic environment. The most promising of these extrinsic explanations is that predation, acting either directly or indirect1y, has delayed density-dependent effects on prey populations during the low phase. The second class of hypotheses proposes that something may be "wrong" with the animals themselves. The most likely intrinsic factors are maternal effects or age effects on fitness during the low phase. Experimental tests for each of these sets of hypotheses are needed, and we suggest replicated experiments on focal species in two continents to resolve these unknowns. (Au)


Tree-climbing by arctic ground squirrels, Spermophilus parryii, in the southwestern Yukon Territory   /   Hubbs, A.H.   Karels, T.   Byrom, A.
(Canadian field-naturalist, v.110, no. 3, July-Sept. 1996, p. 533-534)
(Kluane Boreal Forest Ecosystem Project contribution, no. 78)
References.
ASTIS record 43225.
Languages: English
Libraries: ACU

Arctic Ground Squirrels (Spermophilus parryii) are commonly considered obligate ground-dwelling. However, seventy-eight Arctic Ground Squirrelss were seen climbing or sitting in spruce trees and on deadfall and stumps 164 times in the southwestern Yukon from 1991-1994. Trees, deadfall, and stumps, seemed to serve primarily as temporary refuges and/or predator surveillance sites, although some were occasionally used as nest sites. Arctic Ground Squirrelss are not as obligate ground-dwelling as previously thought. (Au)


A comparison of census methods for red squirrel (Tamiasciurus hudsonicus) and arctic ground squirrel (Spermophilus parryii) populations   /   Sandercock, B.K.   Krebs, C. [Supervisor]
Vancouver, B.C. : University of British Columbia, 1988.
55 leaves : ill., maps ; 28 cm.
(Kluane Boreal Forest Ecosystem Project contribution, no. 80)
Thesis (B.Sc.) - University of British Columbia, Vancouver, B.C., 1988.
References.
ASTIS record 62051.
Languages: English
Libraries: XYKLRS

Five methods were used to measure red squirrel and ground squirrel densities in different habitats near Kluane Lake, Yukon. Counts of red squirrel middens and ground squirrel burrows gave an indirect index of abundance. Live-trapping on middens and burrows captured resident animals whereas traps placed in grids were more likely to capture vagrant adults and dispersing juveniles. Squirrel densities were found to be dependent on the species composition and age structure of the forest. (Au)


Mortality in fledgling Great Horned Owls from black fly hematophaga and leucocytozoonosis   /   Hunter, D.B.   Rohner, C.   Currie, D.C.
(Journal of wildlife diseases, v. 33, no. 3, July 1997, p. 486-491)
(Kluane Boreal Forest Ecosystem Project contribution, no. 81)
References.
ASTIS record 54165.
Languages: English
Web: doi:10.7589/0090-3558-33.3.486
Libraries: AEU

Black fly feeding alone and in concert with Leucocytozoon spp. infection caused mortality in fledgling great horned owls (Bubo virginianus) in the Yukon, Canada 1990 to 1991. These mortalities occurred during a year of food shortage corresponding with a decline in the population of snowshoe hare (Lepus americanus), the main prey for great horned owls. We hypothesize an interaction between food availability and the consequences of host-parasite interactions. (Au)


Impact of food and predation on the snowshoe hare cycle   /   Krebs, C.J.   Boutin, S.   Boonstra, R.   Sinclair, A.R.E.   Smith, J.N.M.   Dale, M.R.T.   Martin, K.   Turkington, R.
(Science, v.269, no.5227, 25 Aug. 1995, p.1112-1115, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 82)
References.
ASTIS record 53365.
Languages: English
Web: doi:10.1126/science.269.5227.1112
Libraries: ACU

Snowshoe hare populations in the boreal forests of North America go through 10-year cycles. Supplemental food and mammalian predator abundance were manipulated in a factorial design on 1-square-kilometer areas for 8 years in the Yukon. Two blocks of forest were fertilized to test for nutrient effects. Predator exclosure doubled and food addition tripled hare density during the cyclic peak and decline. Predator exclosure combined with food addition increased density 11-fold. Added nutrients increased plant growth but not hare density. Food and predation together had a more than additive effect, which suggests that a three-trophic-level interaction generates hare cycles. (Au)


Territorial defence and bequeathal by red squirrel (Tamiasciurus hudsonicus) mothers in the northern boreal forest   /   Price, K.   Ydenberg, R.C. [Supervisor]
Burnaby, B.C. : Simon Fraser University, 1989.
1 v.
(ProQuest Dissertations & Theses publication, no. MM66167)
(Kluane Boreal Forest Ecosystem Project contribution, no. 83)
Thesis (M.Sc.) - Simon Fraser University, Burnaby, B.C., 1989.
Not seen by ASTIS. Citation from NSTP.
ASTIS record 30172.
Languages: English

Female red squirrels (Tamiasciurus Hudsonicus) sometimes bequeath their territories to their offspring. These individual territories are food-based, defended year-round, and are crucial for overwinter survival. Adult red squirrels have a relatively low mortality rate and, on average, breed for three to five years. In this thesis, I ask when and how intensely an individual red squirrel should defend her territory, and when she should cease defence and give the territory to her offspring. Field studies were carried out at two sites in the boreal forest of the southwest Yukon. In its application to territorial defence, the asymmetric war of attrition model predicts that individuals with a higher value territory will invest more in its defence. In playback experiments, breeding females defended more intensely than did non-breeding females, and females with early litters defended more intensely that did females with late litters. Field observations demonstrated a cost of early reproduction in the form of weight loss, and also suggested an increased risk of losing territory. Late-breeding females did not lose weight, suggesting the presence of a seasonal effect allowing late females to recoup energetic expenses more readily. (Au)


Vertebrate community dynamics in the boreal forest of north-western Canada   /   Krebs, C.J.   Sinclair, A.R.E.   Boutin, S.
In: Frontiers of population ecology / Edited by R.B. Floyd, A.W. Sheppard, and P.J. De Barro. - Collingwood, Vic. : CSIRO Publishing, 1996, p. 155-161, ill.
(Kluane Boreal Forest Ecosystem Project contribution, no. 83 [!])
References.
A paper delivered April 1995 in Canberra, Australia as part of the Nicholson symposium - a celebration of the centenary of the birth of A.J. Nicholson.
ASTIS record 63472.
Languages: English
Libraries: QQLA

The vertebrate community of the boreal forests of northern Canada fluctuates dramatically in a ten year cycle focused on the snowshoe hare (Lepus americanus). Since 1986 we have been analysing the structure of this vertebrate community to understand the impact of the hare cycle on all the other species. We have conducted large-scale experiments in a factorial design by adding food and reducing predation pressure. We will complete these experiments in 1996. The majority finding to date for snowshoe hares is of a large interaction between food and predation, so that the combined treatment of reduced predation plus added food delayed the cyclic decline and maintained high numbers. We do not know the mechanism by which the interaction between food and predation occurs. Risk-sensitive foraging and condition-dependent stress responses are possibilities that require further work. (Au)


A comparison of a cyclic and non-cyclic population of snowshoe hares in Kluane, Yukon   /   Jardine, C.   Krebs, C.J. [Supervisor]
Vancouver, B.C. : University of British Columbia, 1995.
viii, 85 p. : ill. ; 28 cm.
(Kluane Boreal Forest Ecosystem Project contribution, no. 84)
Thesis (M.Sc.) - University of British Columbia, Zoology Department, Vancouver, B.C., 1995.
References.
Indexed from michrofiche.
ASTIS record 60527.
Languages: English
Libraries: BVAU

In this study I compared a non-cyclic island population of snowshoe hares (Lepus americanus) with a cyclic mainland population to determine how the dynamics of the two populations differed following a population decline. Both populations had declined to similar low levels by the fall of 1992. During this study the Jacquot Island hare population increased 3.5 fold from the spring of 1993 to the spring of 1994 while the cyclic mainland hare population remained at low densities. I monitored survival and reproduction to determine the proximate causes for the different dynamics seen. I determined that juvenile survival, overwinter adult survival and reproduction were higher on Jacquot Island of 1994. These were the key proximate factors that allowed the Jacquot Island hare population to increase while the mainland population remained at low densities. There was no difference in summer adult survival between the two areas in 1993. I also investigated the ultimate causes for the different dynamics seen in the two areas. Higher reproductive output, and higher overwinter survival did not coincide with better hare condition on Jacquot Island. There were, however, fewer mammalian predators on Jacquot Island than the mainland. Higher early juvenile survival on Jacquot Island coincided with lower numbers of small mammal predators. (Au)


Effects of food addition on a population of Grey Jays   /   Delchanty, B.   Smith, J.N.M. [Supervisor]
Vancouver, B.C. : University of British Columbia, 1995.
vii, 66 p. : ill., maps ; 28 cm.
(Kluane Boreal Forest Ecosystem Project contribution, no. 85)
Thesis (M.Sc.) - University of British Columbia, 1995.
References.
Indexed from microfiche.
ASTIS record 60533.
Languages: English
Libraries: BVAU XYKLRS

Grey jays (Perisoreus canadensis) in the southwest Yukon were provided with supplemental food on three study areas to study the effects of food on territoriality and foraging strategies. Territory sizes and overlap were measured in 1993 and 1994. Territories of food addition grids were 30% smaller than these on grids without access to added food. There was only slightly more overlap between territories on food addition grids compared to controls, and the difference was not statistically significant. Time spent foraging, the rate at which jays made caches, and the weights of jays were measured. These data were used to test four hypotheses about the factors that limit overwinter body masses of jays. Birds on food addition grids made three times as many caches as control birds in a similar amount of time spent foraging. In winter, grey jays with added food spent less time foraging, yet they were able to maintain higher body condition than control birds. These results were consistent with the hypothesis that overwinter weights are limited by both a food shortage and by costs associated with increasing weight. Seasonal trends in body condition differed between birds on food addition grids and those without supplemental food. Birds with added food were in better condition year round, and were able to increase in weight between summer and fall. Control birds lost weight between summer and fall, but then increased dramatically in winter. These different weight trends may represent different caching or cache retrieval strategies. (Au)


Do predation risk and food affect the home ranges of snowshoe hares?   /   Allcock, K.   Sinclair, T. [Supervisor]
Vancouver, B.C. : University of British Columbia, 1994.
55 leaves : ill., maps ; 30 cm.
(Kluane Boreal Forest Ecosystem Project contribution, no. 86)
Thesis (B.Sc.) - University of British Columbia, Vancouver, B.C., 1994.
References.
ASTIS record 62036.
Languages: English
Libraries: XYKLRS

I studied the effects of food addition and exclusion of terrestrial predators on the home range sizes and daily movements of snowshoe hares (Lepus americanus) in the southern Yukon. I used radio telemetry to track individual hares in areas subjected to three experimental treatments - terrestrial predator exclusion (FENCE), predator exclusion and food addition (FOOD&FENCE), and no manipulation (CONTROL) - in order to test three hypotheses regarding food and predation effects. The Optimal Foraging hypothesis predicts that additional food should cause hares to contract their ranges while exclusion of predators should have no effect. The Predator Avoidance hypothesis predicts that hares should not respond to additional food but that exclusion of predators should cause range expansion. The Tradeoff hypothesis predicts that home ranges and movements should be affected by both food addition and predator exclusion. Hares on CONTROL areas had the largest ranges and made the largest daily movements, followed by FENCE hares, then FOOD&FENCE. Assuming that the presence of exclusion fences did not affect hare movements, these results do not fit the predictions made under any of the hypotheses tested. However, if this assumption is false, and if hares voluntarily constrained their movements to remain within the areas of reduced predation risk, the Predator Avoidance and Tradeoff hypotheses would predict range reduction rather than expansion in predator exclusion areas. In this case, the results of this study match the predictions of the Tradeoff hypothesis. More work is needed to determine whether the fences affect hare movements. It is also necessary to investigate home ranges and movements of hares in areas subjected to food addition only. (Au)


Monitoring vertebrate populations using observational data   /   Hochachka, W.M.   Martin, K.   Doyle, F.   Krebs, C.J.
(Canadian journal of zoology, v. 78, no. 4, Apr. 2000, p. 521-529, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 87)
References.
ASTIS record 48674.
Languages: English
Web: doi:10.1139/cjz-78-4-521
Libraries: ACU

Methods for monitoring temporal changes in population size vary from intensive and potentially expensive to less intensive and more easily implemented techniques. In this paper we evaluate the utility of a monitoring technique that can be used to follow many vertebrate species simultaneously at low cost and requires little training of personnel. Observers record the number of individuals seen per hour in the field and these rates of encounter are used as an index of population size. We examine whether encounter rates reflect population size by comparing them with independent censuses of three species over a 7-year period in the boreal forest near Kluane Lake in the southern Yukon Territory. Encounter rates were generally an accurate reflection of variation in population size. In our study system, inter-observer variability did not influence our ability to detect fluctuations in population size: the underlying fluctuations were detected whether data from all or only a group of "high-quality" observers were used. In our study, the benefit of using all available data outweighed the cost of variation among observers because sample sizes were large (averaging over 1200 data points from 33 observers per year). Variation in the length of observation periods did not affect the chance of detecting animals in our study. Encounter rates provide a reasonable index of variation in population size, although caution should be used with species that are uncommon or difficult to detect. (Au)


Reproduction, hibernation, and population regulation of arctic ground squirrels (Spermophilus parryii plesius)   /   Karels, T.J.   Boonstra, R. [Supervisor]
Toronto : University of Toronto, 2000.
xiv, 183 p. : ill., 1 map ; 28 cm.
(ProQuest Dissertations & Theses publication, no. NQ53885)
(Kluane Boreal Forest Ecosystem Project contribution, no. 88)
ISBN 0-612-53885-0
Thesis (Ph.D.) - University of Toronto, Toronto, Ont., 2000.
References.
Indexed from a PDF file acquired from ProQuest Dissertations & Theses.
ASTIS record 53791.
Languages: English
Libraries: OONL XYKLRS

Populations of arctic ground squirrels in the boreal forest of the southwest Yukon were studied in order to answer the following questions: (1) What are the mechanisms of population regulation in arctic ground squirrel populations, (2) How does variation among individuals and their environment influence their reproduction and survival, and (3) How does variation in habitat influence hibernating strategies of arctic ground squirrels? In spring 1996, control densities of ground squirrels were 1.6 per ha, and four other populations ranged in density from 3.2 to 30.1 per ha as a result of a 10-year (1987-96) large scale manipulation of food and predators in the boreal forest of the Kluane Boreal Forest Ecosystem Project. When the Kluane project terminated in spring 1996, I measured population densities, reproduction, emigration, and survival in all populations using live-trapping and radio-telemetry techniques until spring 1998. Arctic ground squirrel populations were strongly regulated because all experimental populations declined to control densities within two years after the termination of the experimental manipulations. Two factors proved strongly density-dependent and hence were regulatory: (1) the proportion of females that weaned their litter and (2) overwinter survival. Simultaneous density-independent changes in weaning rate were also detected and were attributed to changes in the previous year's snow accumulation. Female ground squirrels exhibited positive associations of life history traits. Squirrels in better condition at spring emergence were more likely to give birth, wean their litter, survive to the next breeding season, and reproduce once again. Nearly all females who failed during lactation did not survive to the next breeding season. The overwinter survival rate of females that successfully weaned a litter declined at a greater rate with increasing population density than did squirrels that never gave birth, indicating a cost to reproduction. Ground squirrels hibernated distantly (24 m) from their summer burrows in relation to population density and in open or shrubby habitats that were likely to accumulate the most snow. Increased snow accumulation over hibernacula increased the minimum soil temperatures and decreased the rate of mass loss of hibernating squirrels suggesting a selective mechanism for the ability of ground squirrels to identify habitats that minimize their energy expenditure during hibernation. (Au)


Evaluation of aerial surveys of ptarmigan, Lagopus species   /   Pelletier, L.   Krebs, C.J.
(Journal of applied ecology, v. 35, no. 6, Dec. 1998, p. 941-947, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 89)
References.
ASTIS record 53363.
Languages: English
Web: doi:10.1111/j.1365-2664.1998.tb00011.x
Libraries: ACU

Summary: 1. We evaluated the reliability of aerial surveys to monitor trends in breeding population density of ptarmigan, Lagopus spp., in south-western Yukon, Canada. 2. Aerial surveys provided repeatable indices of density. 3. Aerial indices of density were positively and linearly related to density between areas within the same year. 4. However, aerial indices of density were not positively related to density between years because the aerial index was lower in 1996 than in 1995, while in fact the density of ptarmigan increased. This could be explained by a reduction in the flushing response of ptarmigan in 1996. 5. We caution wildlife managers against a possible inter-year variation in the number of animals that can be seen from the air when conducting aerial surveys. (Au)


Attempt to determine the influence of parasitism on a snowshoe hare population during the peak and initial decline phases of a hare cycle   /   Sovell, J.R.   Holmes, J.C. [Supervisor]
Edmonton, Alta. : University of Alberta, 1993.
xi, 116 p. : ill., maps ; 28 cm.
(ProQuest Dissertations & Theses publication, no. MM88127)
(Kluane Boreal Forest Ecosystem Project contribution, no. 90)
ISBN 0-315-88127-5
Thesis (M.Sc.) - University of Alberta, Edmonton, Alta., 1993.
References.
Indexed from microfiche.
ASTIS record 60538.
Languages: English
Libraries: AEU

Few naturally-occurring host-parasite systems have been experimentally manipulated. Consequently the dynamics of such systems in field are poorly understood. I surveyed the parasites of snowshoe hares, Lepus americanus, at Kluane Lake, southwestern Yukon and examined the potential of two pathogenic nematodes (Protostrongylus boughtoni and Nematodirus triangularis) to affect their population dynamics. Nematode numbers were manipulated in hares by subcutaneous injection (0.4mg/kg) of ivermectin. Two weeks post-treatment, nematode numbers of both species were reduced by approximately 80%. However, beyond two weeks ivermectin did not affect the total number of worms, the maturation of dormant larvae or reinfection by newly acquired larvae. Thus, repeated treatment of individual hares is necessary for successful reduction of worm numbers in the field. Turnover of the hare population was high on both treated and untreated study areas; 70% of the hares were trapped only once. This high turnover reduced the proportion of hares receiving repeated treatments of ivermectin; consequently the manipulation had no effect on overall hare density, recruitment or survival. However, at the level of individual hosts, ivermectin did have an effect. Repeatedly treated hosts were in better body condition and females produced twice times as many offspring as untreated females. In addition, untreated females lost more weight after parturition, and had 45% more of their young die of starvation and exposure. Overall survival did not differ between offspring of treated and untreated hares. My data suggest that the effects of parasites in this population of hares is compensatory to other forms of mortality, that in this population is primarily determined by predation. (Au)


Non-territorial 'floaters' in Great Horned Owls : space use during a cyclic peak of snowshoe hares   /   Rohner, C.
(Animal behaviour, v. 53, no. 5, May 1997, p. 901-912, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 91)
References.
ASTIS record 53735.
Languages: English
Web: doi:10.1006/anbe.1996.0381
Libraries: ACU

The ecology and behaviour of non-territorial owls are little known. During a population peak of snowshoe hares, Lepus americanus, the main prey of great horned owls, Bubo virginianus, in the boreal forest, fledglings were equipped with radio transmitters, and 30 successful dispersers were monitored in 1988-1991. Of those, nine became resident floaters in the study area. Transient floaters were not recorded, although floaters shifted the centre of their home ranges more than territorial owls. Floater home ranges were about five times larger than defended territories, but the space use did not differ significantly. Floaters intruded regularly into territories and their locations overlapped broadly with those of territory owners and other floaters, but were concentrated on the periphery of defended territories. This is consistent with other evidence that territorial behaviour limits the breeding density of great horned owls even at extreme peaks of prey availability. None of the monitored floaters bred as secondary females, and the intrusion rates and movement patterns of floaters did not change during the fertile period of females, as predicted if male floaters were seeking extra-pair copulations. (Au)


A 5-year study of the effects of nutrient availability and herbivory on two boreal forest herbs   /   John, E.   Turkington, R.
(Journal of ecology, v. 85, no. 4, Aug. 1997, p. 419-430)
(Kluane Boreal Forest Ecosystem Project contribution, no. 92 [93])
References.
ASTIS record 43069.
Languages: English
Web: doi:10.2307/2960566
Libraries: ACU

... Summary: 1. The responses of populations of Mertensia paniculata (bluebells or lungwort) and Anemone parviflora (small-flowered anemone) to herbivore exclosure and fertilization in a factorial experiment were monitored over a 5-year period beginning at peak herbivore (hare) densities during the snowshoe hare population cycle. For each species the population density, number and size of leaves and the number of flowers were measured. 2. Both species responded more strongly to fertilizer addition than to the exlusion of herbivores. Mertensia produced more flowering stems, more leaves per stem, and stem density increased in the fertilized plots. Fertilizing increased total leaf length per plant for non-flowering stems but this was not observed for flowering stems. However, the net effect of having more flowering stems and having greater leaf area on non-flowering stems was to increase the total leaf area of the population. The responses of Mertensia make it likely to become a stronger competitor in a more productive plant community. 3. Anemone showed contrasting responses at both individual and population levels. While individual stems produced slightly more leaves in fertilized plots, the density of stems declined. There were no strong effects on either leaf size or flowering. There was evidence of high leaf turnover in fertilized plants. Meanwhile, control and exclosed unfertilized plots showed an increase in population density. 4. The weak responses to herbivory may be explained by the timing; this part of the experiment was run during a period of declining herbivore activity. However, observed interaction effects suggest that those herbivores remaining in the system may be attracted to fertilized plots. It is planned to continue the experiment for at least another 5 years through, and beyond, the next hare peak. ... (Au)


The effects of NPK fertilization for nine years on boreal forest vegetation in northwestern Canada   /   Turkington, R.   John, E.   Krebs, C.J.   Dale, M.R.T.   Nams, V.O.   Boonstra, R.   Boutin, S.   Martin, K.   Sinclair, A.R.E.   Smith, J.N.M.
(Journal of vegetation science, v. 9, no. 3, June 1998, p. 333-346, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 94)
References.
ASTIS record 45454.
Languages: English
Web: doi:10.2307/3237098

Plant productivity is limited by mineral nutrient availability in many boreal forest ecosystems. This study is an analysis of the growth responses of components of a boreal plant community (cryptogams, herbaceous and woody perennials, the dominant shrubs Salix glauca (grey willow) and Betula glandulosa (bog birch) and the dominant tree Picea glauca (white spruce), to the addition of an NPK fertilizer over a nine-year period. The study was carried out in a low-nutrient boreal forest ecosystem in the Yukon Territory in northwestern Canada. The following predictions were tested: (1) That there would be an overall increase in abundance (measured either as cover, density, or dry mass) of all components of the vegetation, (2) that vegetation composition would change as more competitive species increased in abundance and (3) that initial community changes in response to fertilization would be transient. In general, all predictions were found to be true. Species composition changed rapidly in response to fertilizer. Graminoids (e.g. Festuca altaica) and some dicots (e.g. Mertensia paniculata and Achillea millefolium) increased in cover, while other dicots (e.g. Anemone paviflora), dwarf shrubs (e.g. Arctostaphylos uvaursi), bryophytes and lichens declined. There was a significant increase in the growth rate of the two dominant shrubs and of Picea, but not in the cone crop or seed production by Picea. Surveys after 1 or 2 years showed responses by the vegetation but more stable patterns of response did not emerge until after 5 or 6 years. There were consistent and directional changes in the percent cover of some of the herbaceous species on control plots. Growth rates of Salix and Betula varied considerably from year to year, independently of treatment. Long-term studies are essential if we are to understand the role of nutrient limitation in this ecosystem. (Au)


Effects of food and predators on the home-range sizes of arctic ground squirrels (Spermophilus parryii)   /   Hubbs, A.H.   Boonstra, R.
(Canadian journal of zoology, v. 76, no. 3, Mar. 1998, p. 592-596)
(Kluane Boreal Forest Ecosystem Project contribution, no. 95)
References.
ASTIS record 44024.
Languages: English
Web: doi:10.1139/cjz-76-3-592
Libraries: ACU

We used radiotelemetry to study the effects of food addition and predator reduction on the home-range sizes of adult Arctic ground squirrels (Spermophilus parryii) on large-scale experimental grids in the boreal forest of the southwestern Yukon Territory. Home ranges were 2-7 times smaller on food-supplemented grids than on nonsupplemented grids, regardless of whether large mammalian predators were present. Similarly, core areas (where 50% of activities occur) were 8-11 times smaller on food-supplemented grids. Food availability rather than predator presence primarily determined the sizes of home ranges and core areas of Arctic ground squirrels. (Au)


Solar activity and mammal cycles in the Northern Hemisphere   /   Sinclair, A.R.E.   Gosline, J.M.
(American naturalist, v.149, no. 4, Apr. 1997, p. 239-251, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 96)
References.
ASTIS record 53788.
Languages: English
Web: doi:10.1086/286020
Libraries: ACU

To provide background, we mention the salient features of cycles. True cycles (those with reasonably constant periods) are extremely rare in nature, and none are known in the Southern Hemisphere or the Tropics, at least in birds and mammals. Cycles appear confined to northern temperate and subarctic ecosystems. Mammals are unusual in having a range of species that show population cycles (Krebs and Myers 1974; Finerty 1980; Henttonen et al. 1985). The cycle period covers a broad range, from 3-4 yr in small shrews and voles to 10-13 yr in hare species and perhaps longer in larger mammals (Peterson et al. 1984). This period is proportional to body weight to the power of 0.26 (Calder 1983) and so is a species-specific characteristic. ... To summarize our knowledge of mammalian population cycles, we can say that cycle period is related to body size; cycle amplitude is enhanced in higher (northern) latitudes where, perhaps, fewer species interactions allow predator-prey cycles to be expressed; causes of the cycle usually involve both predator and plant trophic levels; and the snowshoe hare has long-term temporal constancy in its cycle period. During high-amplitude sunspot cycles, the hare cycle shows phase lock with sunspots. Also in the snowshoe hare, there is spatial synchrony during the peak phase across the whole boreal forest of North America, a feature that cannot be explained by local dynamics alone and that requires an external synchronizer such as weather acting on a continental scale. Thus, we suggest that weather factors could be entrained by sunspots so that solar activity acts indirectly as the synchronizer of hare cycles through climate. Weather systems have different phase relations with solar activity in different areas of the globe, and so solar-hare phase relations also differ. (Au)


Testing hypotheses of trophic level interactions : a boreal forest ecosystem   /   Sinclair, A.R.E.   Krebs, C.J.   Fryxell, J.M.   Turkington, R.   Boutin, S.   Boonstra, R.   Seccombe-Hett, P.   Lundberg, P.   Oksanen, L.
(Oikos, v. 89, no. 2, May 2000, p. 313-328, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 97)
References.
ASTIS record 53789.
Languages: English
Web: doi:10.1034/j.1600-0706.2000.890213.x
Libraries: ACU

Models of community organization involve variations of the top-down (predator control) or bottom-up (nutrient limitation) hypotheses. Verbal models, however, can be interpreted in different ways leading to confusion. Therefore, we predict from first principles the range of possible trophic level interactions, and define mathematically the instantaneous effects of experimental perturbations. Some of these interactions are logically and biologically unfeasible. The remaining set of 27 feasible models is based on an initial assumption, for simplicity, of linear interactions between trophic levels. Many more complex and non-linear models are logically feasible but, for parsimony, simple ones are tested first. We use an experiment in the boreal forest of Canada to test predictions of instantaneous changes to trophic levels and distinguish between competing models. Seven different perturbations systematically removed each trophic level or, for some levels, supplemented them. The predictions resulting from the perturbations were concerned with the direction of change in biomass in the other levels. The direct effects of each perturbation produced strong top-down and bottom-up changes in biomass. At both the vegetation and herbivore levels top-down was stronger than bottom-up despite some compensatory growth stimulated by herbivory. The combination of experiments produced results consistent with two-way (reciprocal) interactions at each level. Indirect effects on one or two levels removed from the perturbation were either very weak or undetectable. Top-down effects were strong when direct but attenuated quickly. Bottom-up effects were less strong but persisted as indirect effects to higher levels. Although the 'pure reciprocal' model best fits our results for the boreal forest system different models may apply to different ecosystems around the world. (Au)


Fluctuations in home range size of male snowshoe hares during summer breeding season   /   Chu, T.K.Y.   Krebs, C.J. [Supervisor]
Vancouver, B.C. : University of British Columbia, 1996.
45 leaves : ill. ; 30 cm.
(Kluane Boreal Forest Ecosystem Project contribution, no. 99)
Thesis (B.Sc.) - University of British Columbia, Vancouver, B.C., 1996.
References.
ASTIS record 62034.
Languages: English
Libraries: XYKLRS

... I studied the changes in home range size of male snowshoe hares (Lepus americanus) in the southern Yukon during their breeding season in the summer of 1995. Female snowshoe hares can produce up to four litters per breeding season by means of postpartum estrous. I predict that male hares can encounter and fertilize more females by expanding their home ranges during periods when females are most receptive to copulation. I tested this prediction by radio-tracking ten male hares throughout the summer of 1995 and calculating home range estimates for each male for periods of high and low female receptivity. During the breeding season of 1995, female hares produced three distinct litters between May 11 and August 8. Home ranges of male hares were largest during the period of female estrous before the delivery of the second litter. Home ranges size in this period were significantly larger than that of the preceding and subsequent periods. The overall pattern of home range size fluctuation agrees with my prediction that home ranges expand during periods of female estrous except for one discrepancy. No expansion in male home ranges was observed for the period of female estrous preceding the delivery of the third litter. I suspect that the lack of expansion may be due to the fact that third litter young are less profitable than earlier litter groups from a male standpoint. I found no evidence indicating that home range expansion in male hares was constrained by a dominance hierarchy. Male hares did not appear to extend their home ranges equally in all directions. Extensive overlap among male home ranges was maintained throughout the breeding season. (Au)


The effects of food and predation on population regulation of the arctic ground squirrel (Spermophilus parryii plesius) during the peak and decline phases of a snowshoe hare cycle   /   Hubbs, A.H.   Boonstra, R. [Supervisor]
Toronto : University of Toronto, 1994.
xi, 159 p. : ill. ; 28 cm.
(ProQuest Dissertations & Theses publication, no. MM92444)
(Kluane Boreal Forest Ecosystem Project contribution, no. [52])
ISBN 0-315-92444-6
Thesis (M.Sc.) - University of Toronto, Dept. of Zoology, Toronto, Ont., 1994.
References.
Indexed from a PDF file acquired from ProQuest Dissertations & Theses.
ASTIS record 53794.
Languages: English
Libraries: OONL XYKLRS

The relative importance of food and predators in regulating Arctic ground squirrel (Spermophilus parryii plesius (Richardson)) populations was examined in the boreal forest of the southwestern Yukon during the peak and decline of a snowshoe hare (Lepus americanus (Erxleben)) cycle. Squirrels were live-trapped from April to August, 1990-92 on two control grids and on three experimental grids (i.e. Food addition, Food addition and mammalian predator exclusion, and Predator exclusion). Adults on all areas were radio-collared in 1992. Food addition increased densities (3-fold), litter sizes, percentage of females lactating, body weight, and growth rates of juveniles independent of the presence of predators. Survival, recruitment, and immigration were unaffected. Predator exclusion did not significantly improve the survival of radio-collared ground squirrels in 1992 or increase density. Food alone regulated Arctic ground squirrel populations. Predation was relatively unimportant during these phases of the hare cycle. (Au)


Components of regulation of boreal forest understory vegetation : a test of fertilizer and herbivory   /   Dlott, F.   Turkington, R. [Supervisor]
Vancouver, B.C. : University of British Columbia, 1996.
xi, 74 leaves : ill., maps ; 28 cm.
(Kluane Boreal Forest Ecosystem Project contribution, no. [92])
Thesis (M.Sc.) - University of British Columbia, Dept. of Botany, Vancouver, B.C., 1996.
References.
ASTIS record 43160.
Languages: English
Libraries: XYKLRS

This study tests the predictions of two different hypotheses of trophic organization the 'bottom-up' and 'top-down' hypotheses respectively using plants in the boreal forest understory. The experiment manipulated plant resource levels by fertilization and consumer levels (vertebrate herbivory rate) using exclosures, and monitored the response of transplanted seedlings and the leaf area of the established vegetation. Survival and growth transplants was poorest at the highest fertilizer levels; a result not predicted by either 'bottom-up' or 'top-down'. Herbivore exclosures had no significant effects on survival or growth at low or moderate herbivore densities; fertilizer addition did not increase leaf area. These results suggest that the resources added by fertilization and that the herbivores excluded were not limiting at these herbivore densities. At high herbivore densities transplant survival and growth was consistently greater inside exclosures which lends support to the 'top-down' hypothesis for seedling survival and performance, but leaf area did not significantly respond to either treatment but was greater inside exclosures especially when fertilized. A model of trophic relations in the boreal forest between understory plants, their resources and their consumers should only include herbivores as a limiting factor when their densities are abnormally high and even then the 'top-down' hypothesis is supported only from transplant data and not from existing vegetation. (Au)


Do snowshoe hares starve in live-traps? Measurements of overnight weight loss with pertinence to live-trapping techniques   /   DeGroot, J.   Krebs, C.J. [Supervisor]
Vancouver, B.C. : University of British Columbia, 1996.
65 leaves : ill. ; 28 cm.
(Kluane Boreal Forest Ecosystem Project contribution, no. 100)
Thesis (B.Sc.) - University of British Columbia, Vancouver, B.C., 1996.
References.
ASTIS record 62039.
Languages: English
Libraries: XYKLRS

Weight change was measured in snowshoe hares (Lepus americanus) confined in live-traps at Kluane, in the Southwest Yukon. I hypothesized weight loss is experienced in live-traps due to starvation during 3, 5, and 9 hours of overnight confinement in live-traps. Glycogen stores and water are depleted in the initial phase of starvation, followed by fat stores and lean tissue reserves (Hoffer, 1991). Reserves of lean tissue comprise skeletal muscle, and cells of the visceral organs. I proposed that the pattern of weight loss over time in hares would reveal if lean tissue is lost during confinement in traps. If lean tissue is lost, percent weight loss per hour decreases in a declining, exponential trend over time (Hoffer, 1991). In this study, low sample sizes did not allow detection of significant differences in percent weight loss per hour over 3, 5, and 9 hours of confinement in live-traps. Mean percent weight loss was 6.88% (+/-2.01% SD) after 9 hours of confinement in live-traps. Hares also lose weight when deprived of food and water in laboratory experiments. Results were obtained suggesting percent weight loss per hour follows a declining exponential trend during 18 hours of food and water deprivation in the laboratory. Non-linear hypotheses were not tested in this study however, so definite conclusions cannot be made about the pattern of weight loss in field and laboratory experiments. Hares lose weight in live-traps, and laboratory experiments suggest percent weight loss is comparable during 9 hours of food and water deprivation. Hares probably lose weight due to food and water deprivation in live-traps during overnight trapping sessions. I recommend increasing the quantity of apple used to bait live-traps. (Au)


Changes in spatial distributions and movement rates of female snowshoe hares during the breeding season   /   Jekielek, J.   Krebs, C.J. [Supervisor]
Vancouver, B.C. : University of British Columbia, 1996.
52 leaves : ill., maps ; 29 cm.
(Kluane Boreal Forest Ecosystem Project contribution, no. 101)
Thesis (B.Sc.) - University of British Columbia, Vancouver, B.C., 1996.
References.
ASTIS record 62038.
Languages: English
Libraries: XYKLRS

Changes in average movement rates and home-ranges of female snowshoe hares (Lepus americanus) were examined throughout their summer breeding season. Walk-in telemetry and calculation of temporally overlapping home-ranges allowed for high intensity observation of 6 females during this period. Home-ranges varied considerably through time and among hares, and newborn litter locations were often not contained within female home-range estimates. Females shifted the centers of overall home-ranges towards nest-site locations at parturition, while shifting home-range centers away from areas of high-intensity habitat use. Synchronous birthing was also observed among females. Average movement rates were significantly greater pre-parturition than post-partum, and movement rates were positively correlated with home-ranges. A behavioural explanation consistent with the trends in both movement rates and home-ranges, the decoy-role hypothesis, was postulated. In addition, the Minimum Convex Polygon and Adaptive Kernal home-range estimation methods were compared to one another, and differences between them discussed. (Au)


Evaluation of aerial surveys of ptarmigan (Lagopus spp.)   /   Pelletier, L.   Krebs, C.J. [Supervisor]
Vancouver, B.C. : University of British Columbia, 1996.
x, 84 p. : ill. ; 28 cm.
(Kluane Boreal Forest Ecosystem Project contribution, no. 102)
Thesis (M.Sc.) - University of British Columbia, 1996.
References.
Indexed from microfiche.
Kluane Field Station copy contains 77 pages.
ASTIS record 60534.
Languages: English
Libraries: BVAU XYKLRS

Ptarmigan (Lagopus spp.) range over most of the Canadian arctic and alpine; thus, a technique is needed to track their densities over a large scale, which current techniques do not. I evaluated a program of aerial surveys done from 1990 to 1996 at Kluane, Yukon, which could do so. The indices of density obtained from aerial counts were subject to many types of errors. Of these, the counting bias, probably the largest source of bias, could have been corrected partially by using the simultaneous 2-sample capture-recapture method. However, the correction factors were highly imprecise due to the low number of double-counts. The variation of total survey bias (with 5 replicates of the survey over 2 weeks in 1996) was low in comparison to the variability of the indices between years; thus, the technique is repeatable. About 70% of the variability of the index in a given year could be attributed to daily factors. I also calibrated the index using ground counts (line transect estimates based on perpendicular distances). A test of accuracy of the line-transect method on a 0.77 km² grid showed line-transect estimates had low bias (-3 to -7%). The calibration showed a positive and linear relationship between the aerial index and ptarmigan density. However, this calibration held only across areas in the same year. The 1996 index was significantly lower than the 1995 index but the density was higher in 1996. This could be explained by a reduced flushing behaviour in 1996, perhaps caused by increased avian predation pressure. Other indices of abundance of the Kluane ptarmigan population from winter encounter rates are also unreliable as they also predicted a drop in abundance for 1996 while the density actually increased. I recommend the use of line-transects to wildlife managers since the technique provided accurate and fairly precise (%cv = 15-25%) estimates of density. (Au)


Interactions between food and predation in limiting arctic ground squirrel populations   /   Karels, T.J.   Boonstra, R. [Supervisor]
Toronto : University of Toronto, 1996.
vii, 52 p. : ill., maps ; 28 cm.
(ProQuest Dissertations & Theses publication, no. MM12734)
(Kluane Boreal Forest Ecosystem Project contribution, no. 103)
ISBN 0-612-12734-6
Thesis (M.Sc.) - University of Toronto, Dept. of Zoology, Toronto, 1996.
References.
Indexed from a PDF file acquired from ProQuest Dissertations & Theses.
ASTIS record 43461.
Languages: English
Libraries: OONL XYKLRS

I examined the importance of food and predators in limiting populations of Arctic ground squirrels (Spermophilus parryii plesius) in the southwestern Yukon during the low phase of the snowshoe hare (Lepus americanus) cycle from spring 1993 to spring 1995. Live trapping was conducted on four control grids and four experimental treatments (one mammalian predator exclosure grid, two food addition grids, and one mammalian predator exclosure + food addition grid). Squirrels were radio-collared on all treatments to monitor survival both during the active season and overwinter. Reduction of predators doubled population density, increased the percentage of breeding females, produced an increase in the percentage of females producing litters to juvenile emergence, and produced a higher estimated reproductive rate in both years. Food addition maintained higher densities (4-fold), slightly higher active seasonal improved body condition, a greater proportion of females successfully raised litters, advanced juvenile emergence, and greater juvenile growth rate. Predator exclosure + food maintained higher densities (8-fold) and had slightly greater effects than were listed for the food addition treatment. Overwinter survival was not affected by any treatment. Both overwinter survival and active season survival were higher during my study than were previously recorded for Arctic ground squirrels in the boreal forest during the early decline of the hare cycle. I conclude that predation independently has little importance on ground squirrel survival but that it interacts with food abundance to limit ground squirrel populations during the low phase of the snowshoe hare cycle. (Au)


Numerical responses of coyotes and lynx to the snowshoe hare cycle   /   O'Donoghue, M.   Boutin, S.   Krebs, C.J.   Hofer, E.J.
(Oikos, v. 80, no. 1, Oct. 1997, p. 150-162, ill., 1 map)
(Kluane Boreal Forest Ecosystem Project contribution, no. 104)
References.
ASTIS record 53265.
Languages: English
Web: doi:10.2307/3546526
Libraries: ACU

Coyotes and lynx are the two most important mammalian predators of snowshoe hares throughout much of the boreal forest in North America. Populations of hares cycle in abundance, with peaks in density occurring every 8 - 11 yr, and experimental results suggest that predation is a necessary factor causing these cycles. We measured the numerical responses of coyotes and lynx during a cyclic fluctuation of hare populations in the southwest Yukon, to determine their effect on the cyclic dynamics. We used snow-tracking, track counts, and radio telemetry to directly examine changes in the numbers, population dynamics, and movements. Numbers of coyotes varied 6-fold and those of lynx 7.5-fold during a 26 - 44-fold fluctuation in numbers of hares, and the abundances of both predators were maximal a year later than the peak in numbers of snowshoe hares. Cyclic declines in numbers of coyotes were associated with lower reproductive output and high emigration rates. Likewise, few to no kits were produced by lynx after the second winter of declining numbers of hares. High emigration rates were characteristic of lynx during the cyclic peak and decline, and low in situ survival was observed late in the decline. The delayed numerical responses of both 'generalist' coyotes and 'specialist' lynx were therefore similar, and would contribute to the cyclic dynamics. (Au)


Functional responses of coyotes and lynx to the snowshoe hare cycle   /   O'Donoghue, M.   Boutin, S.   Krebs, C.J.   Zuleta, G.   Murray, D.L.   Hofer, E.J.
(Ecology, v. 79, no. 4, June 1998, p.1193-1208, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 105)
References.
ASTIS record 47449.
Languages: English
Web: doi:10.2307/176736
Libraries: ACU

Coyotes and lynx are the two most important mammalian predators of snowshoe hares throughout much of the boreal forest. Populations of hares cycle in abundance, with peaks in density occurring every 8-11 yr, and experimental results suggest that predation is a necessary factor causing these cycles. We measured the functional responses of coyotes and lynx during a cyclic fluctuation of hare populations in the southwest Yukon, to determine their effect on the cyclic dynamics. We used snow-tracking and radio telemetry to examine changes in the foraging behavior of the predators. Coyotes and lynx both fed mostly on hares during all winters except during cyclic lows, when the main alternative prey of coyotes was voles, and lynx switched to hunting red squirrels. Both predators showed clear functional responses to changes in the densities of hares. Kill rates of hares by coyotes varied from 0.3 to 2.3 hares/d, with the most hares killed one year before the cyclic peak, while those of lynx varied from 0.3 to 1.2 hares/d, with the highest one year after the peak. Maximum kill rates by both predators were greater than their energetic needs. The functional response of coyotes was equally well described by linear and type-2 curves, and that of lynx was well described by a type-2 curve. Kill rates by coyotes were higher during the increase in density of hares than during the cyclic decline, while the reverse was true for lynx. Coyotes killed more hares early in the winter, and cached many of these for later retrieval. Lower densities of hares were associated with longer reactive distances of both predators to hares, but with little apparent change in time spent searching or handling prey. In summary, our data show that the two similarly sized predators differed in their foraging behavior and relative abilities at capturing alternative prey, leading to different patterns in their functional responses to fluctuations in the density of their preferred prey. (Au)


Behavioural responses of coyotes and lynx to the snowshoe hare cycle   /   O'Donoghue, M.   Boutin, S.   Krebs, C.J.   Murray, D.L.   Hofer, E.J.
(Oikos, v. 82, no. 1, May 1998, p. 169-183, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 106)
References.
ASTIS record 47624.
Languages: English
Web: doi:10.2307/3546927
Libraries: ACU

Coyotes and lynx are the two most important mammalian predators of snowshoe hares throughout much of the North American boreal forest. Populations of hares cycle in abundance, with peaks in density occurring every 8-11 years. We used snow-tracking to measure the diets, use of habitats, and hunting tactics of coyotes and lynx during a cyclic fluctuation of hare populations in the southwest Yukon. Our objective was to determine changes in foraging behaviour of the predators leading to functional responses to densities of hares. Coyotes and lynx both preferred snowshoe hares over available alternative prey at all phases of the cycle. Lynx switched to preying on red squirrels during the cyclic low and subsequent early increase. The pattern of changes in habitat use by coyotes and lynx paralleled that of snowshoe hares, and both concentrated their hunting activity in areas of high density of hares. Coyotes used more open cover to hunt voles during years of low abundance of hares and high numbers of small mammals. Lynx increasingly used ambush beds for hunting hares and red squirrels during the cyclic decline and low. Hunting success was not higher from beds. Lynx hunted in adult groups for the first time during the cyclic decline and low. (Au)


Roost site selection of Great Horned Owls in relation to black fly activity : an anti-parasite behavior?   /   Rohner, C.   Krebs, C.J.   Hunter, D.B.   Currie, D.C.
(The Condor (Los Angeles, Calif.), v.102, no. 4, Nov. 2000, p. 950-955, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 108)
References.
Short communication.
ASTIS record 53266.
Languages: English
Web: doi:10.1650/0010-5422(2000)102[0950:RSSOGH]2.0.CO;2
Libraries: ACU

We document a shift in roosting behavior of Great Horned Owls (Bubo virginianus) from winter and late spring to summer. During summer, Great Horned Owls roosted near the ground or exposed on open ground, whereas they chose concealed perches at mid-canopy level for the rest of the year as typical for forest owls. This shift of roosting behavior coincided with the emergence of ornithophilic black flies, which transmit avian malaria (Leucocytozoon spp.). The shift in roosting behavior was consistent with measurements of parasite exposure at different habitat positions. Black fly activity was highest at mid-canopy level, and almost no black flies were active on open ground. Ground-roosting was not caused by poorly developed flying capability of juveniles, because solitarily-roosting adult owls showed the same behavioral shift in a second year of study. Black flies and avian malaria are widely distributed, and the effect of the vertical distribution of these parasites in forests on roosting, nesting, and foraging of sylvatic birds deserves further study. (Au)


Does body condition affect fecundity in a cyclic population of snowshoe hares?   /   Hodges, K.E.   Stefan, C.I.   Gillis, E.A.
(Canadian journal of zoology, v. 77, no. 1, Jan. 1999, p. 1-6, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 110)
References.
ASTIS record 47416.
Languages: English
Web: doi:10.1139/cjz-77-1-1
Libraries: ACU

Snowshoe hares (Lepus americanus) undergo a l0-year cycle in abundance, with cyclic changes in reproduction occurring 3 years prior to numeric changes. Reproduction may be associated with body condition, which might change with nutrition or predation pressure. We describe hare body condition (as a mass-skeletal size relationship) through a cycle in the southern Yukon from 1989 to 1996, test the effects of food and predation risk on body condition, and examine whether changes in body condition are related to cyclic reproductive changes. Hare body condition was lowest during the decline phase but rapidly improved during the low phase. Although yearling hares were in poorer condition than adults, changes in age structure cannot explain the cyclic fluctuation in condition. Food addition and predator reduction both resulted in better body condition. Body condition did not affect reproduction. The highest natality occurred when hares were in intermediate condition, while the lowest natality occurred when hares were in the best condition. Although changes in food and predation risk affect hare body condition, we found no relationship between body condition and cyclic reproductive changes. Rather, during times of nutritional deficit, female hares may maintain mass during gestation and lactation, but at a proximate cost to their offspring. Thus, inferences based on indices of condition incorporating body mass may be misleading. (Au)


Seasonal changes in glucocorticoid and testosterone concentrations in free-living arctic ground squirrels from the boreal forest of the Yukon   /   Boonstra, R.   Hubbs, A.H.   Lacey, E.A.   McColl, C.J.
(Canadian journal of zoology, v. 79, no. 1, Jan. 2001, p. 49-58, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 111)
References.
ASTIS record 50475.
Languages: English
Web: doi:10.1139/cjz-79-1-49
Libraries: ACU

We examined how glucocorticoid and testosterone concentrations changed from spring to summer by livetrapping free-living populations of arctic ground squirrels (Spermophilus parryii). The primary glucocorticoid was found to be cortisol, with corticosterone below measurable concentrations in most individuals. Livetrapping elicited a strong stress response in both sexes: breeding males and females trapped in spring had free cortisol concentrations 4 and 34 times, respectively, those of base-line animals. The maximum corticosteroid-binding capacity (MCBC) was unaffected by trapping and was about 3 times higher in breeding females than in breeding males. Over the active season, MCBC values were lowest in all male classes (juveniles, nonreproductive adults, and reproductive adults), being less than half those in all female classes; pregnant females had values approximately twice those of juvenile females. However, free cortisol concentrations were similar in all female classes and in juvenile males and about half those in adult males. Livetrapping increased testosterone concentrations in males over those found in samples from base-line males, and testosterone concentrations did not affect MCBC values. Testosterone concentrations in livetrapped animals differed significantly among male classes, with nonreproductive males maintaining concentrations 64% of those in breeding males and 10 times those in juveniles. (Au)


Increased corticosteroid binding capacity of plasma albumin but not of corticosteroid-binding globulin caused by ACTH-induced changes in free fatty acid concentrations in snowshoe hares and rabbits   /   Boonstra, R.   Tinnikov, A.A.
(Journal of endocrinology, v.156, no. 1, Jan. 1998, p. 205-212, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 111 [109])
References.
ASTIS record 53268.
Languages: English
Web: doi:10.1677/joe.0.1560205
Libraries: ACU

Free fatty acids (FFAs) are rapidly mobilized by ACTH and have been shown to be potent endogenous modulators of steroid-protein interactions. We increased FFA in lagomorphs by ACTH and then separated the transient increase in glucocorticoid binding capacity of plasma into that accounted for by changes in binding to albumin and to corticosteroid-binding globulin (CBG). Sequential injections of dexamethasone and ACTH into both snowshoe hares and laboratory rabbits resulted in the rapid mobilization of FFA only after the ACTH injection. The maximum corticosteroid binding capacity increase paralleled that of the FFA increase in both species. In rabbits, CBG levels remained constant over the length of the experiment. Corticosterone binding by rabbit albumin increased in a dose-dependent fashion in response to increases in FFA (oleic and linoleic acid) concentrations. Finally, by stimulating FFA release in snowshoe hares with ACTH and separating the increase in corticosteroid binding capacity through selective denaturing of CBG by heat, we determined that the increase in plasma binding capacity was a response to changes in binding by albumin, not CBG. Thus FFA released in response to stressors in lagomorphs may effect short-term increases in steroid binding. (Au)


Snowshoe hare demography during a cyclic population low   /   Hodges, K.E.   Krebs, C.J.   Sinclair, A.R.E.
(Journal of animal ecology, v. 68, no. 3, May 1999, p. 581-594, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 112)
References.
ASTIS record 47505.
Languages: English
Web: doi:10.1046/j.1365-2656.1999.00310.x
Libraries: ACU

1. Snowshoe hare (Lepus americanus Erxleben) populations were studied in south-west Yukon during the low phase of the 10-year population cycle. Food availability and predator abundance were manipulated in a factorial design to determine the importance of each factor in hare dynamics during this phase. 2. Food was abundant during the low phase, and snowshoe hares were not food limited. 3. Survival of hares was higher than at any other phase of the cycle, and predators were scarce, but >75% of hare deaths resulted from predation. 4. Food addition resulted in higher hare densities and better body condition than on control sites. There were no observable effects of food addition on population rate of increase, recruitment, survival or age structure. 5. Mammalian predator reduction resulted in higher hare densities, higher survival, better body condition and an older age structure. Relative to control populations, recruitment was lower and population rates of increase similar. 6. The joint manipulation of food addition + predator reduction had greater positive effects on hare density and body condition than either single factor manipulation. Survival was better than on control sites, and the age structure was older than on control sites. Population rates of increase were similar, but recruitment was higher on the control areas. 7. We conclude that snowshoe hare dynamics at the low of the cycle are dominated by the interaction of food and predation. Risk of predation also had indirect effects on snowshoe hare age structure and body condition. (Au)


Linking landscape pattern and forest disturbance : fire history of the Shakwak Trench, southwest Yukon Territory   /   Francis, S.R.   Dale, M.R.T. [Supervisor]
Edmonton, Alta. : University of Edmonton, 1996.
130 p. : ill., maps ; 28 cm.
(ProQuest Dissertations & Theses publication, no. MM18258)
(Kluane Boreal Forest Ecosystem Project contribution, no. 113)
ISBN 0-612-18258-4
Thesis (M.Sc.) - University of Alberta, Edmonton, Alta., 1996.
References.
Indexed from microfiche.
ASTIS record 60542.
Languages: English
Libraries: AEU

In an effort to maintain basic ecosystem processes, new landscape-based forest management initiatives are attempting to emulate natural disturbance patterns. Understanding and characterizing these natural disturbance patterns has therefore become a research priority. In a fire patterned landscape such as the North American boreal forest, fire history studies can aid in obtaining this information. A fire history study was performed in the Shakwak Trench, southwest Yukon Territory, with special emphasis on the spatial occurrence of individual wildfires and their relationship to landscape characteristics. A strong spatial correspondence exists between certain landscape features and the forest disturbance history of the Shakwak Trench. Some locations within this valley have consistently escaped fire for very long periods of time while others have burned frequently. Specifically, nearly all old forests occur on steep north- and east-slope aspects while frequently burned areas are associated with south-and west-slope aspects. Therefore, simply describing an average fire cycle or frequency to characterize the disturbance regime of this area is misleading. The spatial pattern of disturbances on the landscape is of great ecological importance and can exert much control over the forest age-class distribution. (Au)


Indices of population size for burrowing mammals   /   Hubbs, A.H.   Karels, T.   Boonstra, R.
(The Journal of wildlife management, v. 64, no. 1, Jan. 2000, p. 296-301, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 114)
References.
ASTIS record 48537.
Languages: English
Web: doi:10.2307/3803002
Libraries: ACU

There are few quick, precise indices for predicting population size of semifossorial mammals. We assessed the utility of powder-tracking and infrared thermal imaging to predict population size in the Arctic ground squirrel (Spermophilus parryii) in the boreal forest of southwestern Yukon. Density estimated from livetrapping was strongly, and linearly correlated with both indices (r = 0.81 for powder-tracking; r = 0.91 for infrared imaging). The slope of the relationship between density and the infrared index (0.10) deviated from a slope of 1. The slope of the relationship between density and the powder-tracking index (0.82) did not deviate from a slope of 1, but our power to detect departures from this slope using this index was low (0.10). We recommend infrared imaging and powder-tracking for monitoring population sizes of semifossorial mammals. (Au)


Community dynamics of vertebrate herbivores : how can we untangle the web?   /   Krebs, C.J.   Sinclair, A.R.E.   Boonstra, R.   Boutin, S.   Martin, K.   Smith, J.N.M.
(Herbivores : between plants and predators : the 38th symposium of the British Ecological Society in cooperation with the Netherlands Ecological Society held at the Wageningen Agricultural University, Netherlands, 1997 / Edited by H. Olff, V.K. Brown and R.H. Drent. British Ecological Society symposium, no. 38, 1999, ch. 15, p. 447-473, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 115)
References.
ASTIS record 53774.
Languages: English
Libraries: ACU

To answer the important question 'what determines the abundance of herbivores?' we need to study vertebrate community dynamics. We can answer this question either by perturbation experiments or by observing the interactions between the main species in a system for long enough for the natural system variation to illuminate the nexus of interactions. We review our perturbation experiments on the Yukon boreal forest vertebrate community and compare our results with the observational analysis of the long-term dynamics of the Serengeti ungulate community of East Africa and arctic-breeding geese in Europe and North America. We conclude that all vertebrate herbivores are limited primarily in abundance by predation unless they have evolved an escape mechanism in space or time. Bird and ungulate migrations permit escape from predators in space. The properties of each community depend largely on the unique adaptations of the component species. The significant linkages in food webs tend to be vertical rather than horizontal and may be relatively few for each herbivore. This gives us some hope that experimental procedures of less than monumental complexity can untangle the web efficiently. ... Our objective here is to determine those factors that have major effects on abundance. In this regard we will begin by assuming that unless we can double (or halve) numbers in one generation by changing the factor, the effect is too small to be studied by short-term field experiments. We are interested only in large effects. ... (Au)


Survival of juvenile hares during a cyclic population increase   /   Gillis, E.A.
(Canadian journal of zoology, v. 76, no. 10, Oct. 1998, p.1949-1956, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 117)
References.
ASTIS record 47414.
Languages: English
Web: doi:10.1139/cjz-76-10-1949
Libraries: ACU

Snowshoe hares (Lepus americanus) are multilittered synchronous breeders that produce up to four distinct litters of young each summer. I used radiotelemetry to determine the effects of juvenile cohort (i.e., litter group) and food availability on postweaning survival of hares in the southwestern Yukon during the increase phase of a hare cycle. During the study, I monitored 86 juvenile hares from control areas and areas in which supplemental food was provided. Twenty-eight-day survival did not differ between food addition and control areas for any juvenile cohort, and survival rates of juveniles (all cohorts combined) did not differ significantly from those of adults (juveniles: 0.91 per 28 days; adults: 0.93 per 28 days). However, when examined by juvenile cohort, survival of third and fourth litters was significantly lower than that of adults and first and second litters. These differences were the result of differential survival among the juvenile cohorts during a 3-month period in the fall (September-November). Predation was the primary proximate cause of death for weaned juvenile hares, accounting for 86% of deaths. (Au)


Natal dispersal of snowshoe hares during a cyclic population increase   /   Gillis, E.A.   Krebs, C.J.
(Journal of mammalogy, v. 80, no. 3, Aug. 1999, p. 933-939, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 118)
References.
ASTIS record 53777.
Languages: English
Web: doi:10.2307/1383263
Libraries: ACU

We used radiotelemetry to monitor movements of 35 juvenile snowshoe hares (Lepus americanus) from weaning until their first breeding season (June 1995-April 1996). Juveniles born on control or food-addition areas were assigned to one of three cohorts of litters. We calculated natal dispersal distances (distance from nest site to breeding location) and frequencies of emigration (proportion dispersing more than twice the home-range diameter of adults) and determined ages and dates at emigration. Natal dispersal distances ranged from 23 m to >16 km. Fifty percent (9/18) of juveniles that survived until their first breeding season emigrated. Juveniles from the third litter dispersed at an older age than those from first or second litters. We detected no statistically significant effect of food addition on dispersal distance. With our small sample, we did not find statistical evidence of sex-biased natal dispersal (7 of 12 males and 2 of 6 females dispersed). (Au)


15N signatures do not reflect body condition in arctic ground squirrels   /   Ben-David, M.   McColl, C.J.   Boonstra, R.   Karels, T.J.
(Canadian journal of zoology, v. 77, no. 9, Sept. 1999, p.1373-1378, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 119)
References.
ASTIS record 47425.
Languages: English
Web: doi:10.1139/cjz-77-9-1373
Libraries: ACU

Studies using stable-isotope analysis documented an enrichment in delta 15N values in nutritionally stressed animals. Investigators suggested that changes in delta 15N values measured in urine, hair, and blood may be a good indicator of lean-tissue losses. During our investigations into the effects of population density on body condition and reproduction of female Arctic ground squirrels (Spermophilus parryii plesius) near Kluane Lake, Yukon, Canada, we examined the relations between body condition and delta 15N values. Data obtained from 20 livetrapped female ground squirrels suggested that reproductive females from a population with moderate density and low food availability experienced a reduction in body condition, as indicated by mass loss and changes in blood urea nitrogen (BUN) and glucose concentrations. In contrast, those from a population that failed to reproduce successfully and had high density and low food availability experienced no nutritional stress. Similarly, those females from a high-density population with high food availability (i.e., supplemented food) that reproduced successfully suffered no noticeable nutritional stress. In contrast to our prediction, delta 15N values did not show a decline with increasing body mass, and animals in poor and excellent body condition had similar delta 15N values. In addition, female ground squirrels from the same group with access to similar types of food (natural or supplemented) and with similar body masses, BUN, and blood glucose concentrations showed a difference of up to 1.8‰ in delta 15N values. Thus, our results suggest that the ecological process (i.e., diet selection) may have obscured the physiological one (i.e., recycling of nitrogen). Therefore, we recommend that field ecologists studying animal diets using stable-isotope analysis use alternative techniques when attempting to evaluate the body condition of their subjects. (Au)


Response of Great Horned Owls to experimental "hot spots" of snowshoe hare density   /   Rohner, C.   Krebs, C.J.
(The Auk, v.115, no. 3, July 1998, p. 694-705, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 120)
References.
ASTIS record 53781.
Languages: English
Web: doi:10.2307/4089417
Libraries: ACU

Predators that aggregate in "hot spots" of high prey density have been hypothesized to synchronize population cycles of small mammals. During a peak and decline in a snowshoe hare (Lepus americanus) cycle, we created artificial hot spots of increased hare abundance by adding food and excluding mammalian predators on three l-km² blocks and then recorded the response of radio-marked Great Horned Owls (Bubo virginianus) to these food additions. Territorial owls showed a decrease in home range size and patchiness of spatial use as hare densities peaked and declined, although this was better explained by smaller territory sizes due to a growing owl population rather than a direct behavioral response to changing food density. Experimental owls on food-enriched territories did not show a difference in conventional measurements of home-range size and patchiness of spatial use compared with controls, but the distances of owl locations to treatment blocks revealed concentrations of spatial use on experimental hot spots. At a larger scale, neither territorial owls nor nonterritorial floaters showed a tendency to leave poorer patches and move toward hot spots, and the territorial system of Great Horned Owls was largely resistant to extreme variations in prey density. The effect of social interference between predators has been assumed for several models of predator-prey interactions, but empirical evidence has rarely been demonstrated. Our results suggest that territorial behavior, in addition to limiting the growth of a predator population, also prevents large aggregations of predators at an intermediate spatial scale. (Au)


Predation and population cycles of small mammals : a reassessment of the predation hypothesis   /   Korpimäki, E.   Krebs, C.J.
(BioScience, v. 46, no. 10, Nov. 1996, p. 754-764, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 121)
References.
ASTIS record 53772.
Languages: English
Web: doi:10.2307/1312851
Libraries: ACU

... In this article, we have highlighted five major areas, whose careful study will help us to achieve this goal [of understanding the role of predation in small mammal cycles]: [1] We need more comprehensive field data relevant to the six central classifications that are made to evaluate the role of predation - specialist versus generalist, resident versus migratory, numerical versus functional responses, rapid versus time-lagged responses, predator self-regulation, and predation risk effects. We have found large gaps in our current knowledge, especially of predator long-distance movements induced by population cycles of small mammals. ... [2] More effort should be devoted to measuring the time lags between population fluctuations of prey and predator densities, because such lags are critical to our understanding of the stabilizing or destabilizing effects of predation. [3] Territoriality, inter- and intraspecific competition, and intraguild predation among predators are poorly understood. Yet these factors can limit the densities of predators in the peak phase of the population cycle and thus also limit predation mortality in small mammal populations. [4] The indirect effects of predation are currently controversial and present particular difficulties in evaluation for field populations. Unless predation risk can be measured independently, or its level manipulated in the field, arguments that invoke predation risk as an explanation for changes in reproductive and growth rates of small mammals in the course of the population cycle may be circular, because they may be based on spurious correlations between factors in declining populations. Crowded laboratory studies tell us little about the predation risk effects in nature. The fact that small mammals usually live in multipredator environments has also been overlooked in studies on predation risk. ... [5] There is a need for multipredator-multiprey models, but their construction may not be easy task. We also need comprehensive field data from the modeled system to make reliable basic assumptions and to use correct parameter values in the model simulations. ... We list the main predictions of the predator hypothesis for small mammal cycles in Table 1 [1) losses due to predation will be density-dependent or delayed density-dependent; 2) delayed density-dependence will lead to fluctuations in prey numbers; 3) direct density-dependence will not lead to fluctuations in prey populations; 4) reduction or increase of predators will change prey population fluctuations; 5) manipulated risk of predation will alter the indirect effects of predators on prey dynamics; 6) predation mortality is additive rather than compensatory] and suggest some critical experimental tests of these predictions. Four issues should be emphasized in testing these predictions. First, in predator manipulation studies the densities of all main predators should be manipulated. ... Second, we propose large unfenced predator manipulations on mainland sites. ... Third, there is often a lack of sufficient replication in predation manipulation studies .... replicates are necessary if treatment and control areas, rather than animals living on these areas, are to be used as independent observation units in statistical tests. Fourth, the scale of experiments appears to be small in most studies. Many authors have stressed the importance of scale ... but few have been able to work at the proper scale. ... The predator manipulation studies we suggest are time consuming and expensive, and we wonder whether any research council will finance these long-term studies. ... Can the predation hypothesis explain both short-term vole cycles and long-term snowshoe hare cycles? The answer is a tentative yes, because this hypothesis has considerable empirical, theoretical and experimental support. But the answer is tentative, because replicated predator manipulation studies in large unfenced areas are still badly needed and its prediction s need to be tested rigorously. ... (Au)


Physiological effects of three inhalant anesthetics on arctic ground squirrels   /   McColl, C.J.   Boonstra, R.
(Wildlife Society bulletin, v. 27, no. 4, Winter 1999, p. 946-951, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 122)
References.
ASTIS record 53795.
Languages: English
Libraries: ACU

Restraint of small mammals may be necessary for procedures such as attaching radio-collars or collecting blood samples. Additionally, when manual restraint is not sufficient, chemical restraint may be required to prevent injury to the animal and to the handler. However, the responses of mammals to chemical restraint are often either unknown or species-specific. We compared effects of 3 inhalant anesthetics (halothane, isoflurane, and methoxyflurane) and manual restraint on induction and recovery time, stress response, and hematological parameters in Arctic ground squirrels (Spermophilus parryil) in a field setting. Forty squirrels were live-trapped, randomly assigned to treatments, and released after recovery. Methoxyflurane (x±SE: 69.3±5.9 sec) had a greater induction time (ANOVA, P<0.001) than halothane and isoflurane, but isoflurane (19.5±1.8) and halothane (9.2±0.8) did not differ. All anesthetics differed (P<0.001) in recovery times: methoxyflurane (198.0±21.0) had the slowest recovery time, isoflurane was intermediate (124.7±2.95), and halothane was the most rapid (66.4±5.95). Time to immobilize and collect the blood sample with manual restraint took about twice as long (146.4±11.4). Mean free cortisol levels (range: 81.5-91.8 nmol/L), glucose levels (range: 80.3-94.7 mg/dl), and hematocrits (range: 40.4-42.2%) were similar in all treatments; maximum corticosteroid binding capacity was greater (P<0.05) in squirrels anesthetized with halothane (125.8±3.87 nmol/L) than in other treatments (range: 100.3-118.8). We recommend using methoxyflurane for field use when portable anesthetic units are not accessible. (Au)


Proximate factors affecting snowshoe hare movements during a cyclic population low phase   /   Hodges, K.E.
(Écoscience, v. 6, no 4, 1999, p. 487-496, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 123)
References.
ASTIS record 47461.
Languages: English
Web: doi:10.1080/11956860.1999.11682558
Libraries: ACU

Animals change their movements in response to food supply and predation risk. Such behavioural shifts can affect reproduction and survival, especially if animals are forced to trade off between food and safety. I studied snowshoe hares (Lepus americanus Erxleben) during a low phase of the ten-year cycle in the southern Yukon. I used a factorial manipulation of food addition and predator reduction to determine how predators, food supply, and hare density affect hare movements. Control hares were more active than hares protected from predators or hares given supplemental food. Female hares showed no change in home range size or winter travel rates with these treatments, but females protected from predators had lower summer travel rates than did control females. Male hares protected from predators had lower travel rates in both seasons and smaller home ranges than did males exposed to mammalian predators. Male hares generally had higher movements than did females, but neither sex responded to a ~5-fold change in density. The results indicate that different movement indices have distinct functions that may differ with sex. Not all movement types are necessarily affected by predation risk, food availability, or density. The increase in movements with higher risk is unusual, because most small mammals reduce movements when predation risk is high. For snowshoe hares, safety may increase by moving away from predators and using larger areas. (Au)


Biases in the estimation of the demographic parameters of a snowshoe hare population   /   Haydon, D.T.   Gillis, E.A.   Stefan, C.I.   Krebs, C.J.
(Journal of animal ecology, v. 68, no. 3, May 1999, p. 501-512, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 124)
References.
ASTIS record 47504.
Languages: English
Web: doi:10.1046/j.1365-2656.1999.00309.x
Libraries: ACU

1. Survival rates and natalities for a population of snowshoe hares in the Yukon were estimated independently of and simultaneously with estimates of population change during the increase phase of a hare cycle. 2. Simple demographic models are used to show that even though the estimated survival rates and natalities were high relative to previously published estimates, the observed demographic parameters are unable to explain the extent of population increase, and we conclude that some of these parameters must be underestimates. 3. A sensitivity analysis is used to examine the potential influence of changes in these demographic parameters on the population growth rate. During most years of the hare cycle the population growth rate is potentially most sensitive to changes in juvenile postweaning survival. Only during crash years is adult survivorship likely to be a more important determinant of the rate of population change. 4. Examination of previously published data sets on two full population cycles suggests that while survival rates are positively correlated with population growth rates, their incorporation into demographic models results in frequent underestimation of the rate of population increase. (Au)


Contrasting stress response of male arctic ground squirrels and red squirrels   /   Boonstra, R.   McColl, C.J.
(Journal of experimental zoology, v.286, no. 4, 1 Mar. 2000, p. 390-404, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 125)
References.
ASTIS record 53269.
Languages: English
Web: doi:10.1002/(SICI)1097-010X(20000301)286:4<390::AID-JEZ7>3.0.CO;2-O
Libraries: ACU

A hormonal-challenge protocol was used to compare the stress response of males of Arctic ground squirrels and red squirrels during the breeding season (May). These squirrels live in the same boreal forest of the Yukon, but have very different life histories and utilize the forest in markedly different ways. Red squirrels had levels of total cortisol, maximum corticosteroid-binding capacity, and free cortisol that were 5, 7, and 2 times, respectively, those of Arctic ground squirrels. Red squirrels were resistant to suppression by an artificial glucocorticoid, dexamethasone (DEX); Arctic ground squirrels were not. Cortisol levels in red squirrels responded slowly but continuously to the ACTH injection; Arctic ground squirrels responded rapidly and then stabilized. Testosterone levels in red squirrels were extremely sensitive to the challenge, being suppressed by both DEX and ACTH; levels in Arctic ground squirrels were resistant to the challenge, being modestly suppressed by DEX and stimulated by ACTH. Energy mobilization, as measured by glucose and free fatty acid responses, was not affected. Red squirrels had four times the levels of white blood cells and higher proportions of lymphocytes and lower proportions of eosinophils than Arctic ground squirrels, indicating that the latter were in worse condition immunologically. Our evidence suggests that the functions associated with the hypothalamic-pituitary-adrenal axis are compromised in breeding male Arctic ground squirrels, but not in red squirrels. We propose that in male red squirrels this axis has evolved in the context of a stable social system based on long-lived animals with individual territories which are needed to deal with unpredictable winter food supplies. In contrast, Arctic ground squirrels escape the rigors of winter by hibernation and this hormonal axis has evolved in short-lived males in the context of intense intra-sexual competition in a social system based on female kin groups and regular male dispersal to avoid inbreeding. (Au)


Does predation risk cause snowshoe hares to modify their diets?   /   Hodges, K.E.   Sinclair, A.R.E.
(Canadian journal of zoology, v. 81, no. 12, Dec. 2003, p.1973-1985, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 126)
References.
ASTIS record 53337.
Languages: English
Web: doi:10.1139/z03-192
Libraries: ACU

Snowshoe hares (Lepus americanus) undergo a 10-year population cycle with several years of low densities. Several authors have suggested that snowshoe hares modify their foraging behaviour to reduce predation risk during the low phase, resulting in protein-poor diets and poor body condition. We test that idea by using a factorial manipulation of food supplementation and predator reduction and by examining the species composition, browse size, and nutritional quality of snowshoe hare diets during 3 years of low snowshoe hare abundance in southwestern Yukon. Our results negate the hypothesis that snowshoe hares change their diets in response to mammalian predators during the cyclic low phase. Snowshoe hares on the different treatments had diets that differed in species composition and twig sizes, but protected hares did not have higher protein diets than unprotected hares. Snowshoe hares with access to supplemental food ate more fibrous and lower protein natural browse than unfed hares, showing that they did not choose diets primarily for protein content. Instead, snowshoe hares converted a wide range of forage availabilities into similar intakes of protein and fibre, despite variation in predator presence. Our results suggest that snowshoe hares select their diets to balance the protein and fibre contents. Although sublethal effects of predators may influence cyclic dynamics, our results show that such a feedback does not occur via a nutritional mechanism, counter to previous suggestions. (Au)


Experimental manipulation of predation and food supply of arctic ground squirrels in the boreal forest   /   Byrom, A.E.   Karels, T.J.   Krebs, C.J.   Boonstra, R.
(Canadian journal of zoology, v. 78, no. 8, Aug. 2000, p.1309-1319, ill., 1 map)
(Kluane Boreal Forest Ecosystem Project contribution, no. 127)
References.
ASTIS record 48681.
Languages: English
Web: doi:10.1139/cjz-78-8-1309
Libraries: ACU

We examined whether arctic ground squirrel (Spermophilus parryii plesius) populations in northern boreal forest in the Yukon Territory, Canada, were limited by food, predators, or a combination of both, during the decline and low phases of a snowshoe hare cycle. From 1990 to 1995, populations were monitored in large-scale (1 km²) experimental manipulations. Squirrels were studied on eight 9-ha grids: four unmanipulated control grids, two food-supplemented grids, a predator-exclosure grid, and a predator-exclosure + food-supplemented grid. Population density was measured on all grids by livetrapping and active-season survival was measured using radiotelemetry. Population densities were lowest in 1992 and 1993 (2 years after the snowshoe hare population decline). Rates of population change were negative from 1991 to 1993, when predation pressure was most intense after the snowshoe hare decline, and positive from 1993 to 1995, when hares and predators were at low densities. Predation accounted for 125 of 130 mortalities (96%) of radio-collared squirrels. Adult survival was significantly lower in 1992 and 1993 than in 1994 and 1995, and was a strong predictor of annual rates of population change in arctic ground squirrels. Treatments were ranked as follows in their effect on adult survival: predator exclosure + food-supplemented > food-supplemented > predator exclosure > controls. Juvenile survival was lowest in 1992, and food addition and predator removal separately increased juvenile survival. On average, predator exclusion increased population densities twofold, food supplementation increased densities fourfold, and food supplementation and predator removal together increased densities 10-fold. We conclude that food and predation interact to limit arctic ground squirrel populations in the boreal forest during the decline and low phases of the snowshoe hare cycle. The snowshoe hare cycle may indirectly create a lagged secondary fluctuation in arctic ground squirrel populations through shared cyclic predators. (Au)


Why are arctic ground squirrels more stressed in the boreal forest than in alpine meadows?   /   Hik, D.S.   McColl, C.J.   Boonstra, R.
(Écoscience, v. 8, no 3, 2001, p. 275-288, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 128)
References.
ASTIS record 50485.
Languages: English
Web: doi:10.1080/11956860.2001.11682654
Libraries: ACU

Arctic ground squirrels (Spermophilus parryii plesius Richardson) in the southeastern Yukon live in both boreal forest and alpine tundra habitats. We live-trapped young male and female squirrels in both habitat types and subjected them to a standardized hormonal-challenge protocol to assess the responsiveness of their hypothalamic-pituitary-adrenal axis. Alpine squirrels had levels of free cortisol at the baseline (initial) bleed following their removal from traps that were 3 times higher in males and 5 times higher in females compared with boreal forest squirrels. Females, but not males, from the boreal forest were dexamethasone resistant, while neither sex from the alpine habitat was resistant. Free cortisol in alpine squirrels also responded more dramatically after the injection of adrenocorticotropic hormone. Corticosteroid-binding globulin levels were significantly lower in forest than alpine squirrels and these levels were not markedly affected by the challenge protocol. Glucose levels were significantly higher in boreal than alpine squirrels and the pattern differed between the two sites in response to the protocol. Hematocrits were significantly higher in alpine squirrels. Collectively, this evidence suggests that Arctic ground squirrels were more chronically stressed in the boreal forest than in the alpine meadows. The most likely explanation for our results is higher predation risk in the forest compared with alpine meadows, as forage availability and population density were not significantly different between the two habitats. (Au)


Population dynamics response of Lupinus arcticus to fertilization, clipping, and neighbour removal in the understory of the boreal forest   /   Graham, S.A.   Turkington, R.
(Canadian journal of botany, v. 78, no. 6, June 2000, p. 753-758, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 129)
References.
ASTIS record 48373.
Languages: English
Web: doi:10.1139/cjb-78-6-753
Libraries: ACU

A demographic study was conducted on field populations of Lupinus arcticus S. Wats. growing in the understory of a white spruce dominated forest, near Kluane Lake, Yukon. The relative effects of soil fertility level, neighbours, and herbivory were assessed using a factorial experiment of ± fertilizer (N-P-K), ± neighbour removal, and ± clipping. We monitored the dynamics of leaves and collected data on reproduction, survival, and size for two growing seasons. Fertilizing increased the incidence of disease on leaves and reduced reproductive efficiency. Clipping reduced leaf cohort survivorship, total leaf density, and the incidence of disease on leaves. Removing neighbours increased the percent cover of L. arcticus and decreased total leaf mortality. Treatments had no effect on the survival of leaves in early cohorts. Although there were some significant responses to treatments, the overall tendency was a lack of response, especially pertaining to leaf population dynamics. This low response to the treatments imposed is consistent with the argument that plants growing in low productivity, infrequently disturbed habitats should show little response to short-term changes in local environmental conditions. The results are also consistent with suggestions that plants in moderately stressed habitats should be more adapted to withstand grazing than competition. (Au)


Natal dispersal of juvenile arctic ground squirrels in the boreal forest   /   Byrom, A.E.   Krebs, C.J.
(Canadian journal of zoology, v. 77, no. 7, July 1999, p.1048-1059, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 130)
References.
ASTIS record 47421.
Languages: English
Web: doi:10.1139/cjz-77-7-1048
Libraries: ACU

Natal dispersal is assumed to be costly because of the risk of mortality, yet rarely are movement patterns and survival of dispersers observed directly. We determined the fates and dispersal distances of 150 radio-collared juvenile arctic ground squirrels from 1993 to 1995 at Kluane, Yukon Territory, Canada (61°N, 138°W). We tested the hypothesis that dispersal has a high mortality cost, and we also attempted to distinguish among three hypotheses to explain natal dispersal: competition for mates, competition for resources, and inbreeding avoidance. Juveniles were radio-collared at emergence from the natal burrow on five 9-ha grids nested within larger (1 km²) experimental manipulations: two controls, a predator exclosure, a food-supplemented grid, and a predator exclosure + food grid. In all years and on all areas, dispersing juveniles were more likely to die than philopatric squirrels, and the risk of mortality increased with distance from the natal burrow for both sexes. Overall, survival of philopatric squirrels was 73%, whereas survival of dispersing squirrels ranged from a maximum of 40% to a minimum of 25%. Juvenile females were strongly philopatric, independent of population density, except on the predator exclosure + food grid in 1995, where population density was extremely high and resources other than food were probably limiting. Resource competition may explain patterns of philopatry and dispersal in female arctic ground squirrels. Juvenile males moved farther from their natal site than females and more of them died. Males also had a strong tendency to disperse that was independent of food availability or population density, which suggests that male arctic ground squirrels ultimately may disperse to avoid either inbreeding with female relatives or intrasexual competition for mates. (Au)


The interactive effects of food and predators on reproduction and overwinter survival of arctic ground squirrels   /   Karels, T.J.   Byrom, A.E.   Boonstra, R.   Krebs, C.J.
(Journal of animal ecology, v. 69, no. 2, Mar. 2000, p. 235-247, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 131)
References.
ASTIS record 48524.
Languages: English
Web: doi:10.1046/j.1365-2656.2000.00387.x
Libraries: ACU

1. We examined the effects of food and predators on population limitation in the arctic ground squirrel (Spermophilus parryii plesius Richardson) in the boreal forest of the south-western Yukon. We focused on ground squirrel reproduction and overwinter survival. 2. Squirrel populations were monitored by live-trapping and radio-telemetry from 1993 to the spring of 1996 on four control and four experimental areas (one predator exclosure treatment, two food addition treatments, and one predator exclosure plus food addition treatment). 3. Predator exclusion increased body condition, percentage lactating, percentage weaning litters, litter size, and doubled population density relative to controls, but had no effect on juvenile growth rate, overwinter survival, or juvenile emergence date. 4. Food addition advanced juvenile emergence date and increased adult body condition, percentage lactating, percentage weaning litters, litter size, population density relative to controls (4-7 fold), but had no effect on juvenile growth rate of overwinter survival. 5. Predator exclusion combined with food addition increased adult body condition, percentage lactating, percentage weaning litters, and population density relative to controls (19-fold). 6. We conclude that arctic ground squirrels in the boreal forest are limited by an interaction between food and predation, acting primarily through changes in reproduction, and that their impact on density was multiplicative. (Au)


Impact of predation on burrow use by arctic ground squirrels in the boreal forest   /   Karels, T.J.   Boonstra, R.
(Proceedings of the Royal Society of London. Series B. Biological sciences, v.266, no.1433, 22 Oct. 1999, p.2117-2123, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 132)
References.
ASTIS record 53270.
Languages: English
Web: doi:10.1098/rspb.1999.0896
Libraries: ACU

In sedentary animals, the choice of a suitable home site is critical to survival and reproductive fitness. However, habitat suitability may vary with predation risk. We compared habitat use of Arctic ground squirrels (Spermophilus parryii plesius) living in the boreal forest under conditions of fluctuating predation pressure. In our study area, predators show ten-year cycles in numbers that track that of their primary prey, the snowshoe hare (Lepus americanus). In 1993, we compared burrows that continued to be occupied following the period of intense predation during the hare decline of 1990-1992 with those that became vacant, and with random locations. We contrasted these sites to those in a predator exclosure where predation pressure was minimized. Burrows on control sites were located on sloped sites with high visibility. Burrows that remained occupied during the period of intense predation were more likely to be in open areas with fewer fallen trees than burrows that became vacant. We used discriminant functions derived from the control sites and found that 89% of the burrows on the predator exclosure were classified as being similar to the random locations on control sites. We conclude that the distribution of Arctic ground squirrels in the boreal forest is a direct function of predator presence. (Au)


Reproduction at all costs : the adaptive stress response of male arctic ground squirrels   /   Boonstra, R.   McColl, C.J.   Karels, T.J.
(Ecology, v. 82, no. 7, July 2001, p.1930-1946, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 134)
References.
ASTIS record 50477.
Languages: English
Web: doi:10.2307/2680058
Libraries: ACU

We tested the hypothesis that adult male arctic ground squirrels (Spermophilus parryii plesius) exhibit an adaptive stress response during the mating period that may compromise their survival, whereas males at other times (nonreproductive adult males and juvenile males) have a normal functional stress response. We assessed the physiological responsiveness of the stress axis, of energy mobilization, and of the immune response by subjecting adult breeding males, adult nonbreeding males, and juvenile males to a hormonal challenge and an immunocompetence challenge. At the onset of the breeding season in spring, only 25-30% of the population were males, and of those present during the mating period, half disappeared soon thereafter, and 82% were not replaced by immigrants. Adult breeding males had the highest levels of free cortisol, the lowest maximum corticosteroid-binding capacity, slight dexamethasone resistance, the lowest hematocrit, the lowest number of white blood cells, the highest number of eosinophils, and the poorest ability to respond to the foreign antigen challenge in comparison with the other two male classes. All of these characteristics were indicative of chronic stress in breeding males that may directly compromise their survival. Juvenile males in mid-August also showed many, but not all of these characteristics, indicative of a prolonged period of stress, presumably associated with the period of dispersal. Testosterone levels remained high irrespective of age or breeding condition, decreased when dexamethasone was injected, and increased when ACTH was injected. These latter results are unique in mammals. High testosterone levels and their augmentation with stressors may play a key role in maintenance of aggressive behavior. We conclude that breeding male arctic ground squirrels exhibit an adaptive stress response in which they trade off survival for reproduction. We hypothesize that similar stress responses may have evolved in other species with comparable life histories. (Au)


Reducing solar heat gain during winter : the role of white bark in northern deciduous trees   /   Karels, T.J.   Boonstra, R.
(Arctic, v. 56, no. 2, June 2003, p. 168-174, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 135)
References.
ASTIS record 51824.
Languages: English
Web: http://pubs.aina.ucalgary.ca/arctic/Arctic56-2-168.pdf
Web: doi:10.14430/arctic612
Libraries: ACU

Deciduous tree species throughout the boreal forest of North America have lighter-coloured bark than do species restricted to more southern forests. We tested the hypothesis that light-coloured bark minimizes the thawing and freezing of cambium tissue during winter that could contribute to sunscald injury. During mid-winter, maximum midday cambium temperatures of south-exposed bark of white birch (Betula papyrifera Marsh.) near Timmins, Ontario, were higher for brown-painted bark (+1.6 °C) than for natural bark (-9.4 °C) and white-painted bark (-12.1 °C). Rates of temperature decrease after trees were shaded at midday were more rapid for brown-painted bark (0.06 °C/min) than for natural bark (0.03 °C/min) and white-painted bark (0.03 °C/min). When stems of white birch, trembling aspen (Populus tremuloides Michx.), yellow birch (B. alleghaniensis Britton), and largetooth aspen (P. grandidentata Michx.) were illuminated and subsequently shaded at -10 °C ambient air temperature, maximum cambium temperatures and rates of cambium cooling increased with decreasing measures of whiteness. For trembling aspen in the southwest Yukon, we found that after two years, brown-painted trees had a higher incidence (35%) of wounding that resembled sunscald injury than did white-painted trees (2.5%) and natural trees (4.5%). Therefore, we suggest that light-coloured bark reduces the risk of winter sunscald injury, probably by protecting the cambium from solar heat gain in subfreezing temperatures. This physical mechanism for reducing sunscald risk may explain why the deciduous trees at the northern limit of tree growth are those with highly reflective bark. (Au)


Cyclic dynamics of snowshoe hares on a small island in the Yukon   /   Krebs, C.J.   Zimmerling, T.N.   Jardine, C.   Trostel, K.A.   Kenney, A.J.   Gilbert, S.   Hofer, E.J.
(Canadian journal of zoology, v. 80, no. 8, Aug. 2002, p.1442-1450, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 135 [!])
References.
ASTIS record 51845.
Languages: English
Web: doi:10.1139/z02-143
Libraries: ACU

Snowshoe hare (Lepus americanus) populations were monitored from 1977 to 2001 on Jacquot Island (5 km²) in Kluane Lake, southwestern Yukon, and on nearby mainland sites. Jacquot Island hares averaged twice the density of mainland control populations and, although they show 10-year cycles, fluctuate with much lower amplitude than mainland populations. Three separate intensive studies over 6 years attempted to determine what caused these differences. We tested two hypotheses to explain the dynamics. Reproductive rates of hares were similar on Jacquot Island and the mainland. Adult survival rates were higher on the island in most years, with the exception of years of population decline. Juvenile survival rates from 0 to 30 days of life were much higher on the island than on the mainland except for decline summers. The adult- and juvenile-survival differences between the island and the mainland were explained most consistently by predation. Improved survival on the island is correlated with a reduction in the numbers and types of predators found on Jacquot Island compared with the mainland. In particular, red squirrels were rare on Jacquot Island, arctic ground squirrels were absent, and the larger predators, like lynx and great-horned owls, were sporadic in occurrence on this small island. (Au)


Differential predation by coyotes on snowshoe hares   /   Hodges, K.E.
(Canadian journal of zoology, v. 79, no. 10, Oct. 2001, p.1878-1884, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 136)
References.
ASTIS record 50442.
Languages: English
Web: doi:10.1139/cjz-79-10-1878
Libraries: ACU

Differential predation on particular sex or age classes of a population can arise as a result of predator preferences or prey attributes. I examined the impacts of age, size, and body mass of snowshoe hares, Lepus americanus, on their susceptibility to predation by coyotes, Canis latrans. I observed coyote predation on naïve radio-collared hares during a fortuitous natural experiment: a coyote entered a predator exclosure fence in which hares of all ages had no previous experience with terrestrial predators, thus separating age from experience with this predator. I contrasted this manipulation with populations in which hares grew up in the presence of coyotes. Prey naiveté per se did not influence coyote predation, but older hares appeared to be more susceptible to coyote predation than younger ones. There were no obvious effects of body mass or size on coyote predation during the winter. (Au)


Overwinter mass loss of snowshoe hares in the Yukon : starvation, stress, adaptation or artefact?   /   Hodges, K.E.   Boonstra, R.   Krebs, C.J.
(Journal of animal ecology, v. 75, no. 1, Jan. 2006, p. 1-13, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 138)
References.
ASTIS record 57774.
Languages: English
Web: doi:10.1111/j.1365-2656.2005.01018.x
Libraries: ACU

Summary: 1. Overwinter mass loss can reduce energetic requirements in mammals (Dehnel's phenomenon). Alternatively, mass loss can result from food limitation or high predation risk. 2. We use data from fertilizer, food-supplementation and predator-exclusion experiments in the Yukon during a population cycle from 1986 to 1996 to test the causes of overwinter mass loss by snowshoe hares (Lepus americanus). In all years, some hares on control sites gained mass overwinter. During the increase phase the majority gained mass, but in all other phases the majority lost mass. 3. Snowshoe hares weighing < 1000 g in autumn always gained mass overwinter, as did the majority that weighed 1000-1400 g. Hares weighing > 1800 g in autumn usually lost mass. 4. Snowshoe hares on the predator-exclosure + food site gained mass overwinter in all years. Hares on the food-supplementation sites lost mass during the decline but gained mass in all other phases. Fertilization had little effect on mass dynamics. 5. Snowshoe hares were more likely to lose mass during winters with low survival rates. Snowshoe hares on the predator-exclosure treatments were more likely to gain mass than were hares on control sites. 6. Overwinter mass loss was correlated with maximum snow depth. At equivalent snow depths, hares on food-supplemented areas lost 98 g (± 14·6 SE) less on average than hares on the controls and predator-exclosure treatment. 7. Bone-marrow fat was related to body mass and cause of death. Small hares had the lowest marrow fat. Hares killed by humans had higher marrow fat than those killed by predators; hares that simply died had the lowest marrow fat. Hares on food-supplemented sites had the highest kidney and marrow fat. 8. Overwinter-mass loss for snowshoe hares is explained interactively by winter conditions, food supply, predation risk and autumn mass. Some snowshoe hares lost mass overwinter in all years and on all treatments, suggesting that reducing body mass may facilitate survival, especially in cases where foraging costs are high energetically or increase predation risk. (Au)


Population ecology of arctic ground squirrels in the boreal forest during the decline and low phases of a snowshoe hare cycle   /   Byrom, A.E.   Krebs, C.J. [Supervisor]
Vancouver, B.C. : University of British Columbia, 1997.
xiii, 206 p. : ill. ; 28 cm.
(Kluane Boreal Forest Ecosystem Project contribution, no. 139)
(ProQuest Dissertations & Theses publication, no. NN19557)
ISBN 0-612-19557-0
Thesis (Ph.D.) - University of British Columbia, Dept. of Zoology, Vancouver, B.C., 1997.
Appendices.
References.
ASTIS record 54188.
Languages: English
Libraries: XYKLRS

I examined food and predation as factors limiting arctic ground squirrel (Spermophilus parryii plesius) populations during the decline and low phase of a snowshoe hare cycle (1992 - 1995). Food and predator limitation were tested experimentally with large-scale (36-ha) experimental manipulations: two food-supplemented areas, a predator exclosure, and a food-supplemented treatment where predators were also excluded. Predator removal doubled population density, while addition of food resulted in a four-fold density increase. Removal of predators and addition of food together resulted in a 10-fold increase in arctic ground squirrel population densities. Population densities and adult survival rates were lower in 1992 and 1993 (two years after the snowshoe hare population decline) than in 1994 and 1995. Food supply and predation interact to limit arctic ground squirrel population densities in the boreal forest during the decline and low phases of the snowshoe hare cycle. Supplemental food did not affect dispersal distances or dispersal frequency of 172 radio-collared juveniles of either sex in any year. Juveniles that moved farther from their natal burrow were more likely to die. Males moved farther than females and died more frequently. Dispersal tendency was unrelated to population density in males. Females increased their tendency to disperse only on a study site with population densities 17 × those of control populations. Male arctic ground squirrels probably disperse to avoid inbreeding, while females may disperse in response to resource limitation at very high densities. Philopatric females had higher fitness than females that dispersed, particularly if survival during dispersal was taken into account. As population density increased from 1992 - 1995, home range overlap of adult females also increased, as daughters survived to reproductive age in contact with their mother's home range. A stage-based simulation model of the annual cycle of activity and hibernation in arctic ground squirrels was strongly sensitive to adult and juvenile female survival. Arctic ground squirrel populations in the boreal forest can sustain a positive rate of population increase during the low phase of the snowshoe hare cycle, facilitated by flexibility of adult female home range overlap and high adult female survival. (Au)


Factors restricting plant growth in a boreal forest understory : a field test of the relative importance of abiotic and biotic factors   /   Arii, K.
Vancouver, B.C. : University of British Columbia, 1996.
99 p. : ill.
(Kluane Boreal Forest Ecosystem Project contribution, no. 140)
Thesis (M.Sc.) - University of British Columbia, Dept. of Botany, Vancouver, B.C., 1996.
Appendix.
References.
Not seen by ASTIS. Citation from NSTP.
ASTIS record 43161.
Languages: English

This study tests some of the conflicting predictions made by Grime (1977, 1979) and Tilman (1982, 1988) on how competition intensity changes along a gradient of nutrient availability. This was tested by applying three levels of nutrients (fertilizer treatments) and by varying the amount of neighbors present (competition treatments) in a factorial design using five common herbacious species found in the boreal forest understory (Achillea millefolium, Anemone parviflora, Festuca altaica, Lupinus arcticus, Mertensia paniculata). Competition intensity indices (CI) were calculated from the final biomass and leaf number for each species at all fertility levels. Addition of fertilizer significantly increased biomass and leaf number of A. millefolium and F. altaica. Anemone parviflora had high mortality in fertilized plots, while L. arcticus and M. paniculata did not respond to fertilizer treatments. None of the species responded significantly to the varying amounts of neighbors present in the natural habitat. Competition intensity (CI) values were not significantly different from zero at any of the fertility levels for three out of the four species used to calculate CI. The results support neither of the original predictions made by Grime nor Tilman. However, the lack of response by these species is consistent with another of Grime's predictions based on his arguments about the evolution of stress-tolerance: i.e. his so-called 'stress-tolerant' species adapted to live in habitats of extremely low resource availability. (Au)


Responses of coyotes and lynx to the snowshoe hare cycle   /   O'Donoghue, M.   Krebs, C.J. [Supervisor]
Vancouver, B.C. : University of British Columbia, 1997.
xii, 180 p. : ill., 1 map ; 28 cm.
(ProQuest Dissertations & Theses publication, no. NN19633)
(Kluane Boreal Forest Ecosystem Project contribution, no. 141)
ISBN 0-612-19633-X
Thesis (Ph.D.) - University of British Columbia, Dept. of Zoology, Vancouver, B.C., 1997.
References.
Indexed from a PDF file acquired from ProQuest Dissertations & Theses.
ASTIS record 53790.
Languages: English
Libraries: OONL XYKLRS

Coyotes and lynx are the two most important mammalian predators of snowshoe hares throughout much of the boreal forest. Populations of hares cycle in abundance, with peaks in density occurring every 8-11 years, and experimental results suggest that predation is a necessary factor causing these cycles. We measured the numerical and functional responses of coyotes and lynx during a cyclic fluctuation of hare populations in the southwest Yukon, to determine their effect on the cyclic dynamics. We used snow-tracking, track counts, and radio telemetry to directly examine changes in the numbers, population dynamics, and foraging behaviour of the predators. Numbers of coyotes varied 6-fold and those of lynx 7.5-fold during a 26-44-fold fluctuation in numbers of hares, and the abundances of both predators were maximal a year later than the peak in numbers of snowshoe hares. Cyclic declines in numbers of coyotes and lynx were associated with lower reproductive output and high dispersal rates, and low in situ survival of lynx later in the decline. Coyotes and lynx both fed mostly on hares during all winters except during cyclic lows, when the main alternative prey of coyotes was voles, and lynx switched to hunting red squirrels. Both predators showed clear functional responses to changes in the densities of hares. Kill rates of hares by coyotes varied from 0.3 to 2.3 hares/day, with the most hares killed one year before the cyclic peak, while those of lynx varied from 0.3 to 1.2 hares/day, with the highest one year after the peak. Coyotes killed more hares early in the winter, and cached many of these for later retrieval. Based on these estimates, the combined effect of predation by coyotes and lynx ranged from 9.1% to 46.5% of the total winter population of hares killed. There were several changes in foraging behaviour of the predators over the cycle. Habitat use by coyotes and lynx varied, and roughly paralleled trends in habitats used by hares. Lynx increasingly used hunting beds for ambushing both hares and red squirrels during the cyclic decline and low. Lynx also hunted in adult groups for the first time during the decline and low in hare numbers. (Au)


Snowshoe hare demography and behaviour during a cyclic population low phase   /   Hodges, K.E.   Sinclair, A.R.E. [Supervisor]
Vancouver, B.C. : University of British Columbia, 1998.
xiii, 230 p. : ill., maps ; 28 cm.
(ProQuest Dissertations & Theses publication, no. NQ27162)
(Kluane Boreal Forest Ecosystem Project contribution, no. 142)
ISBN 0-612-27162-5
Thesis (Ph.D.) - University of British Columbia, Vancouver, B.C., 1998.
Indexed from a PDF file acquired from ProQuest Dissertations & Theses.
Appendices.
References.
ASTIS record 52976.
Languages: English
Libraries: OONL XYKLRS

Snowshoe hares, Lepus americanus, undergo a ten-year population cycle. I examined whether hares respond behaviourally to predators, and whether hare behaviour influenced population dynamics. If behaviour reduces hares' condition and fecundity, that could explain why the low phase lasts two to four years. I used a factorial manipulation of food addition and predator reduction in southwestern Yukon to test their effects on hare behaviour and demography. Two areas had food added, one area was fenced to exclude mammalian predators, and one area combined both manipulations. Hares densities were low from 1993 to 1995, and increased after summer 1995. Adult survival was similar throughout. Most deaths were due to predation, despite low densities of predators. Although all treatments had higher hare densities, the manipulations started in the previous increase phase, and densities are probably due to earlier dynamics. Populations increased simultaneously on all sites. Hares on control sites ate more protein and less fibre than did hares elsewhere. These differences resulted from the species and twig sizes they ate. Hares on food addition sites had better overall diets, indicated by lower faecal fibre. On all treatments, hares preferred habitats with little open ground and dense clusters of willow. Hares used the thickest cover when resting, and used more exposed sites while foraging. In summer, they preferred deadfall for immediate cover, but in winter they preferred spruce. Male hares, but not females, had larger home ranges when predators were present. Summer movement rates were also higher on sites with predators. Hares did not respond behaviourally to manipulations of food or predators. Food availability was high and predation risk low: hares may employ many different behavioural strategies with similar demographic impacts. There is no support for a behaviourally-mediated explanation for the demography or duration of the low phase. Adult survival and fecundity did notchange, which implies that changes in juvenile survival are crucial to population dynamics. Although behaviour does not appear to affect demography during the low phase, it may do so during the increase and especially the decline phases, when food is more limiting and predation more severe. (Au)


Natal dispersal and post-weaning survival of juvenile snowshoe hares during a cyclic population increase   /   Gillis, E.A.   Krebs, C.J. [Supervisor]
Vancouver, B.C. : University of British Columbia, 1997.
viii, 96 p. : ill. ; 28 cm.
(Kluane Boreal Forest Ecosystem Project contribution, no. 143)
Thesis (M.Sc.) - University of British Columbia, Vancouver, B.C., 1997.
Appendices.
References.
Indexed from microfiche.
ASTIS record 60524.
Languages: English
Libraries: ACU XYKLRS

Juvenile snowshoe hares (Lepus americanus) in southwestern Yukon were monitored using radio telemetry to determine the effects of litter group on natal dispersal and post-weaning survival. A total of 84 juveniles representing the four litter groups born in 1995 were monitored from June 1995 to April 1996 on control areas and areas in which supplemental food was provided. Natal dispersal distance, age and date of emigration, survival rate, and proximate cause of death were examined. Natal dispersal distances (distance from nest site to site of first breeding) of hares ranged from 23 m to over 16 km. Fifty percent (9/18) of juveniles whose nest sites were known and survived until their first breeding season were classified as emigrants (dispersed a distance further than two adult home range diameters). Emigrants did not suffer significantly higher mortality than those individuals which did not emigrate. Neither dispersal distance nor the proportion of hares which emigrated differed between food addition and control areas. On the control areas, there was no evidence of sex-biased natal dispersal. However, on the food addition areas, a higher proportion of males than females emigrated and males dispersed significantly farther than females. This pattern possibly resulted from the increased population density on the food addition areas. Age at emigration varied from 31 days to 140 days, but was not related to the sex of the individuals. Food addition had no observable effect on emigration age, however there was a significant effect of litter group. Third litter juveniles emigrated at an older mean age (84 days) than first (48 days) and second (42 days) litter juveniles. Twenty-eight day survival did not differ between food addition and control areas for any litter group. Over the study period, 28-day survival of juveniles (all litters combined) did not differ significantly from adults (juveniles: 0.91, adults: 0.93). However, when examined by litter group, third litter survival was significantly lower than adult and second litter survival, while fourth litter survival was significantly lower than adult, first, and second litter survival. These differences were the result of differential survival among the litter groups during a three month period in the fall (September-November). Predation was the primary proximate cause of death for weaned juvenile hares, accounting for 86% (37/43) of deaths. Although the dominant predators of juvenile snowshoe hares were annual residents, avian predation was low after November while mammalian predation was constant from mid-August through April. No collared weaned juveniles died before mid-August. (Au)


Reproduction and pre-weaning juvenile survival in a cyclic population of snowshoe hares   /   Stefan, C.I.   Krebs, C.J. [Supervisor]
Vancouver, B.C. : University of British Columbia, 1998.
ix, 104 p. : ill., 1 map ; 28 cm.
(Kluane Boreal Forest Ecosystem Project contribution, no. 144)
Thesis (M.Sc.) - University of British Columbia, Vancouver, B.C., 1998.
Appendices.
References.
Indexed from microfiche.
ASTIS record 60525.
Languages: English
Libraries: BVAU XYKLRS

Reproductive output and pre-weaning survival were estimated in a cyclic population of snowshoe hares (Lepus americanus) in the Kluane Lake region of southwest Yukon Territory. Data collected by five researchers were collated over eight years (1989 - 1996). Pregnant hares were captured and held in cages until they gave birth, so that reproductive characteristics could be measured. Newborn hares were radio-tagged to estimate survival rates from birth. Pregnancy rate litter size and neonate size fluctuated significantly throughout the cycle, changing about two years before corresponding changes in density. The lowest and highest values for all measured parameters were recorded during the decline and increase phases, respectively. Pregnancy rates were nearly 100% in litters born early in the breeding season, but declined up to 20% in the last litter of the year. The number of litters produced in a breeding season varied between two (decline phase) and four (low, early increase). Litter sizes varied among litters within a year, with larger litters being born later in the breeding season. Litter sizes also differed among years, ranging from a mean of 3.8 during the decline to 5.5 during the increase. The weight and size of neonates varied by 5-33% among years. Predation was the primary cause of death of leverets in all phases of the cycle except the decline, when exposure and starvation claimed most young hares. Juvenile survival was highly variable among litter groups at peak hare densities and extremely poor during the decline, particularly Litter 2. Survival was still variable but higher during the low, and was consistently high during the increase. Red squirrels were the primary predators of leverets <10-d old and showed a strong functional response to increasing leveret density across years, particularly in Litter 2. The combined changes for reproduction and early juvenile survival produced a 10-field variation in pre-weaning recruitment of juvenile hares. The indirect effect of predators on the foraging behaviour and physiology of adult females and direct predation on very young hares were implicated as the cause of these changes. My results support the premise that both reproduction and early juvenile survival strongly influence the population growth rate of snowshoe hares. (Au)


Habitat use and nest searching success of red squirrels at a forest edge   /   Pelech, S.A.   Smith, J. [Supervisor]
Vancouver, B.C. : University of British Columbia, 1999.
viii, 80 p. : ill. ; 28 cm.
(Kluane Boreal Forest Ecosystem Project contribution, no. 145)
Thesis (M.Sc.) - University of British Columbia, 1999.
Appendices.
References.
Indexed from microfiche.
ASTIS record 60535.
Languages: English
Libraries: BVAU XYKLRS

Recent declines in many songbird populations have been attributed to forest fragmentation (Robinson et al. 1995), particularly to elevated rates of nest predation at forest edges. Numerous studies have found an increase in predation rates at forest edges (Paton 1994). However, few studies have tested the processes involved; specifically the habitat use and searching behaviour of individual nest predators. I examined factors influencing the nest searching success of red squirrels (Tamiasciurus hudsonicus), a common predator of songbird nests in North American forests. I tested the hypotheses that (1) red squirrels select forest edge habitat, (2) squirrels initially depredate nests opportunistically, (3) with experience, squirrels search actively for nests, and (4) squirrels use an area-restricted search or use nest microhabitat as a search cue to find nests. I monitored the behaviour and habitat use of individual red squirrels over two summers at a forest-pipeline edge in the south-western Yukon Territory. I tested the influence of nest location, squirrel habitat use and amount of prior nest-finding experience on the survival of 2 artificial nests on each of 40 red squirrel territories. Artificial nests contained Japanese quail and plasticine eggs, and were placed at the base of willow shrubs. I used sand-filled trackboards to record small-scale changes in microhabitat use by squirrels after nests were depredated. Such changes could indicate the use of area-restricted searching or microhabitat-based search cues. Red squirrels selected forest-pipeline edges in late spring and early summer. Selection of edges by squirrels was highly correlated with a greater abundance of white spruce buds at edges. Although squirrels preferred edges for foraging, I found no difference in the survival of artificial nests between forest edge and interior locations. Smaller scale patterns of habitat use by individuals were also not related to nest survival. However, squirrels found second nests on their territory in one-fifth the time required to find the first nest. Further survival of the first nest was most closely related to whether a squirrel had depredated a nest the previous year. Squirrels returned to willow nest sites after nests had been found, but did not change their use of similar microhabitats at larger spatial scales. Therefore, neither area-restricted search nor microhabitat-based search cues explain how squirrels efficiently located second nests on their territory. My results support the hypotheses that red squirrels select forest edge habitat and search actively for nests. Although nest survival was not related to the location of squirrel activity, I cannot reject the hypothesis that predation by squirrels is initially opportunistic. Squirrels may locate nests by chance during random searches when the abundance of traditional foods is low and caching activities are infrequent. I found that squirrels learned to search for nests, thus squirrels could show a functional response to increasing nest densities. Densities of both squirrels and songbirds can change in fragmented landscapes and I discuss how such changes may influence rates of nest predation. Additional tests are required to determine how squirrels learn to search for natural nests. Olfactory cues may be important for this and other mammalian predators. Future studies should continue to focus on individual predators and relate the survival of natural nests to visual and olfactory cues, and to nest density. (Au)


From patterns to processes : phase and density dependencies in the Canadian lynx cycle   /   Stenseth, N.C.   Falck, W.   Chan, K.-S.   Bjørnstad, O.N.   O'Donoghue, M.   Tong, H.   Boonstra, R.   Boutin, S.   Krebs, C.J.   Yoccoz, N.G.
(Proceedings of the National Academy of Sciences of the United States of America, v. 95, no. 26, Dec. 22, 1998, p.15430-15435, ill., maps)
(Kluane Boreal Forest Ecosystem Project contribution, no. 146)
References.
ASTIS record 53786.
Languages: English
Web: doi:10.1073/pnas.95.26.15430

Across the boreal forest of North America, lynx populations undergo 10-year cycles. Analysis of 21 time series are generated by nonlinear processes with regulatory delays. Trophic interactions between lynx and hares cause delayed density-dependent regulation of lynx population growth. The nonlinearity, in contrast, appears to arise from phase dependencies in hunting success by lynx through the cycle. Using a combined approach of empirical, statistical, and mathematical modeling, we highlight how shifts in trophic interactions between the lynx and the hare generate the nonlinear process primarily by shifting functional response curves during the increase and the decrease phases. (Au)


Secondary defense responses of white spruce (Picea glauca) and arctic lupine (Lupinus arcticus) to changes in herbivory and soil nutrient concentrations   /   Sharam, G.J.-D.   Turkington, R. [Supervisor]
Vancouver, B.C. : University of British Columbia, 1997.
viii, 64 leaves : ill., maps ; 28 cm.
(Kluane Boreal Forest Ecosystem Project contribution, no. 147)
Thesis (M.Sc.) - University of British Columbia, Dept. of Botany, Vancouver, B.C., 1997.
Appendix.
References.
ASTIS record 43071.
Languages: English
Libraries: XYKLRS

White spruce (Picea glauca, Voss) contains an antifeedant (camphor) which deters snowshoe hares (Lepus americanus Erxleben), a generalist herbivore, from feeding on it. Spruce was used as a model species to test the sometimes conflicting predictions of the Optimal Defense, and the Carbon: Nutrient Balance (CNB) theories of plant defense. The Optimal Defense theory predicts that plants will produce inducible defenses, this concentration being a function of the intensity of herbivore attack, and soil fertility. The CNB theory predicts that changes to the carbon: nutrient ratio will alter the relative amount of available carbon in the plant, and thus, the amount of defensive investment. Twig samples of white spruce were collected from small (0.5-1 m tall), medium (2-3 m), and large (6-10 m) trees growing in areas which have had Herbivore Exclusion, Fertilization, and Herbivore Exclusion + Fertilization treatments for 9 years. Twig samples were also collected from a group of medium-sized trees on Control and Fertilized areas that had been exposed to low and high levels of simulated herbivory. Medium and large trees were also sampled repeatedly during a period of fifteen months to examine yearly patterns of defensive investment. Medium and large trees on Herbivore Exclusion and Fertilization treatment areas had reduced defenses, with additively reduced defenses on the Herbivore Exclusion + Fertilization treatment area. Small tree defenses did not vary between treatment areas. Medium-sized trees exposed to low levels of simulated herbivory decreased defenses within the same year as treatment, and increased defenses the year after treatment. Medium-sized trees exposed to high levels of simulated herbivory had reduced defenses in both the same and the year following treatment. A yearly defense cycle was detected, with a minimum in June-July, and maximum in December-January. Results suggest that spruce trees defend both optimally and as a response to carbon: nutrient limitation. A modified CNB theory is proposed that addresses problems in the original CNB theory, and has better predictive abilities. The defensive content (spartein) of arctic lupines (Lupinus arcticus S. Watts) was also investigated. No variation in defenses was found between lupines on different treatment areas. Spartein concentration was found to cycle on a daily basis, with a maximum at 2 am and a minimum from 10 am to 6 pm. The results of the lupine study are included in an appendix. (Au)


The influence of herbivores and neighboring plants on risk of browsing : a case study using arctic lupine (Lupinus arcticus) and arctic ground squirrels (Spermophilus parryii plesius)   /   Frid, L.   Turkington, R.
(Canadian journal of zoology, v. 79, no. 5, May 2001, p. 874-880, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 149)
References.
ASTIS record 50482.
Languages: English
Web: doi:10.1139/cjz-79-5-874
Libraries: ACU

We examined how herbivore distribution and density, neighboring plant density and species composition, and individual plant morphology all influence the risk that individual arctic lupines (Lupinus arcticus) will be browsed by arctic ground squirrels (Spermophilus parryii plesius). Risk of being browsed was significantly influenced by the number of resident ground squirrels but not by overall squirrel density at a site. As the leaf density of neighboring conspecifics increased, risk of browsing to an individual lupine decreased except when palatable neighbors were also present. The presence of other palatable species increased the risk of browsing. Risk was highest when both lupine and other palatable neighbors were present. The presence of unpalatable neighbors reduced the risk of browsing of individual lupines. We discuss these results in the context of three hypotheses: (1) attractant decoy, (2) resource concentration, and (3) repellent plant. No single hypothesis accounts for our observations, but an interaction between herbivores, neighbors, and individual lupine morphology determined risk of browsing. (Au)


The influence of rainfall on murid densities through a trophic chain in the Kluane boreal forest, Yukon   /   Carrier, P.   Krebs, C.J. [Supervisor]
Vancouver, B.C. : University of British Columbia, 1998.
vii, 51 p. : ill. ; 28 cm.
(Kluane Boreal Forest Ecosystem Project contribution, no. 150)
Thesis (M.Sc.) - University of British Columbia, Vancouver, B.C., 1998.
Appendices.
References.
Indexed from microfiche.
ASTIS record 60536.
Languages: English
Libraries: BVAU

Vole and mouse population densities in the Kluane boreal forest (Yukon) vary non-cyclically; densities are usually low but unpredictable and ephemeral high densities occaionally occur. Anecdotal observations suggest that vole and mouse densities could be correlated to summer rainfall amounts. Small mammal populations in Kluane are suspected to be food-limited, and food production is suspected to be rainfall-limited, since the Kluane boreal forest experiences a water-deficit during the summer. I tested the hypothesis that rainfall acts through a trophic chain to influence vole numbers, and that vole numbers should increase with rainfall two-to-three fold as they do with addition of sunflower seed. To simulate increased rainfall, I installed irrigation systems and operated them for two summers on three areas of approximately 1.5 hectares of boreal forest habitat. I monitored small mammals, mushrooms, understory vegetation, spruce trees and forest-floor invertebrates. Three unirrigated acres of equal size were used as control grids: treatment and control grids were paired within three different sites. Mushrooms and one species of understory plant (Arctostaphylos uva-ursi) responded significantly to the treatment. There was no clear treatment effect on spruce trees, invertebrates, and shrews. Voles were generally more numerous on the treatment grids than on the controls, but the difference was of the expected three-fold magnitude at only one site. Overall, only one out of three sites supported the hypothesis that vole densities can be affected by rainfall through a trophic chain. (Au)


Population regulation in snowshoe hare and Canadian lynx : asymmetric food web configurations between hare and lynx   /   Stenseth, N.C.   Falck, W.   Bjørnstad, O.N.   Krebs, C.J.
(Proceedings of the National Academy of Sciences of the United States of America, v. 94, no. 10, May 13, 1997, p.5147-5152, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 151)
References.
ASTIS record 53785.
Languages: English
Web: doi:10.1073/pnas.94.10.5147

The snowshoe hare and the Canadian lynx in the boreal forests of North America show 9- to 11-year density cycles. These are generally assumed to be linked to each other because lynx are specialist predators on hares. Based on time series data for hare and lynx, we show that the dominant dimensional structure of the hare series appears to be three whereas that of the lynx is two. The three-dimensional structure of the hare time series is hypothesized to be due to a three-trophic level model in which the hare may be seen as simultaneously regulated from below and above. The plant species in the hare diet appear compensatory one to another, and the predator species may, likewise, be seen as an internally compensatory guild. The lynx time series are, in contrast, consistent with a model of donor control in which their populations are regulated from below by prey availability. Thus our analysis suggests that the classic view of a symmetric hare-lynx interaction is too simplistic. Specifically, we argue that the classic food chain structure is inappropriate: the hare is influenced by many predators other than the lynx, and the lynx is primarily influenced by the snowshoe hare. (Au)


The influences of herbivores and neighbouring plants on risk of browse : a case study using arctic lupine (Lupinus arcticus S. Wats) and arctic ground squirrels (Spermophilus parryii)   /   Frid, L.
Vancouver, B.C. : University of British Columbia, 1998.
1 v. : ill., maps.
(Kluane Boreal Forest Ecosystem Project contribution, no. 152)
Thesis (B.Sc. Honours) - University of British Columbia, Vancouver, B.C., 1998.
Appendix.
References.
Not seen by ASTIS.
ASTIS record 45453.
Languages: English

Various factors were tested for their influence on the probabilities that an individual lupine (Lupinus arcticus S. Wats: Fabaceae) was browsed by late June and late July. Risk of browse was significantly influenced by (i) the number of resident ground squirrels at nearby burrow systems, (ii) ground squirrel density at a site, (iii) the leaf density of conspecific, other palatable species and unpalatable species in the patch an individual lupine is found in, and (iv) the number of leaves on an individual lupine. The distance from a lupine to the nearest ground squirrel burrow entrance had no influence on the probability that that lupine was browsed. (Au)


The role of animal behavior studies in wildlife science and management   /   Martin, K.
(Wildlife Society bulletin, v. 26, no. 4, Winter 1998, p. 911-920, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 158)
References.
ASTIS record 53796.
Languages: English
Libraries: ACU

In the early 1980s, I became interested in why male willow ptarmigan (Lagopus lagopus), unlike other grouse species, provided parental care to its offspring. I wondered whether bi-parental care was necessary to raise offspring in the open tundra habitats. I quickly realized that behavioral ecology of game species was a vacant niche. ... Despite the separation between wildlife and behavioral ecology, there is evidence of an emerging interest from both disciplines to find common ground .... I discuss here the value of integrating animal behavior approaches into wildlife science. I summarize the similarities and differences of the 2 disciplines and discuss potential research and management problems that would benefit from both perspectives. Currently, the proximate goals and methods of animal behavior and wildlife science and management studies are divergent; however, the ultimate aims of the 2 disciplines are converging as both groups share the increasingly common goals of understanding and maintaining healthy, free-living wildlife populations in progressively altered landscapes. ... The Kluane [Boreal Forest Ecosystem] Project was a large-scale, multi-taxa, multi-trophic level wildlife ecology study in the southwestern Yukon that examined the structure and function of he vertebrate community in the boreal forest .... Using both experimental and observational approaches, the study examined factors that might cause the snowshoe hare (Lepus americanus) 10-year cycle and the consequences of the hare cycle for the other major vertebrate species in the community .... In the Yukon study, the early integration of behavioral approaches allowed a more accurate census of numbers of raptors after the breakdown in territorial behavior, added other linkages to the food web, reconciled the fact that hares remained a low density after the crash despite availability of food, and explained why hare survival was reduced on the fenced plots. These data were useful in explaining patterns of both numerical and functional responses to the experimental treatments. Thus, the integration of detailed behavioral studies with standard wildlife science methods allowed a more comprehensive understanding of community dynamics, both as support for expected patterns and as explanation for counterintuitive results. ... in Austria, scientists from the Konrad Lorenz Institute of Comparative Ethology, the Research Institute of Wildlife Ecology at the University of Veterinary Medicine, and the Department of Wildlife Biology and Game Management at the University of Agricultural Sciences, Vienna, hold a joint seminar series, and interact regularly on a number of wildlife research problems. ... These expanded multi-disciplinary perspectives by wildlife ecologists, ... are desirable and necessary to meet our professional goals of maintaining healthy populations in functioning communities and ecosystems. (Au)


Reproductive changes in a cyclic population of snowshoe hares   /   Stefan, C.I.   Krebs, C.J.
(Canadian journal of zoology, v. 79, no. 11, Nov. 2001, p.2101-2108, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 159)
References.
ASTIS record 50444.
Languages: English
Web: doi:10.1139/cjz-79-11-2101
Libraries: ACU

Reproductive output was estimated for a cyclic population of snowshoe hares (Lepus americanus) in the Kluane Lake region of the southwest Yukon Territory. Data collected by five researchers were collated over 8 years (1989-1996). Pregnant hares were captured and held in cages until they gave birth so that reproductive characteristics could be measured. Pregnancy rate, litter size, and neonate size fluctuated significantly throughout the cycle, changes occurring about 2 years before corresponding changes in density. Pregnancy rates were nearly 100% early in the breeding season, but declined up to 20% in the last gestation periods of the year. The number of litters produced in a breeding season varied between two (decline phase) and four (low, early increase phase). Litter size varied among years as well as among litters within a year, larger litters being born later in the breeding season. The body mass and size of newborn hares varied by 5-33% among years. The combined changes in pregnancy rate and litter size resulted in a cyclic change in total reproductive output ranging from a low of 6.9 young per female during the decline phase to a maximum of 18.9 during the second year of the low and early increase phases. (Au)


Survival of dispersing versus philopatric juvenile showshoe hares : do dispersers die?   /   Gillis, E.A.   Krebs, C.J.
(Oikos, v. 90, no. 2, Aug. 2000, p. 343-346, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 161)
References.
ASTIS record 48786.
Languages: English
Web: doi:10.1034/j.1600-0706.2000.900215.x
Libraries: ACU

We used radio-telemetry to monitor the survival of dispersing and philopatric juvenile snowshoe hares (Lepus americanus) in southwestern Yukon Territory, Canada, during a cyclic population increase. Neither 28-d survival nor the proportion of hares surviving to breed differed significantly between juvenile hares that dispersed and those that did not, nor was there a significant relationship between dispersal distance and fate (dead or alive). Our results indicate that the overall survival cost associated with natal dispersal is low for snowshoe hares during the early increase of the hare cycle. (Au)


Browse site selection by snowshoe hares : effects of food supply and predation risk   /   Hodges, K.E.   Sinclair, A.R.E.
(Canadian journal of zoology, v. 83, no. 2, Feb. 2005, p. 280-292, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 162)
References.
ASTIS record 60064.
Languages: English
Web: doi:10.1139/z05-015
Libraries: ACU

If snowshoe hares (Lepus americanus Erxleben, 1777) change their foraging behaviour through the population cycle as food supply and predation pressure change, these shifts could contribute to their population cycles by affecting survival and reproduction. We examined whether hares change their foraging movements and browse site selection in response to manipulations of food addition and predator reduction during a cyclic low phase. Snowshoe hares on sites with supplemental rabbit chow ate fewer species per site and preferred to browse in slightly denser cover than unfed hares. Differences in foraging behaviour were linked to season and site characteristics. Snowshoe hares moved similar distances and spent similar amounts of time per browse site in the presence and absence of terrestrial predators. Hares protected from predators used slightly more browse sites in thick cover, but this pattern was partially due to differences in availability. The absence of terrestrial predators had little effect on snowshoe hare foraging behaviour; instead, browse distribution patterns explained most of the behavioural variation. Thus, the predicted patterns in response to the manipulations did not occur, and our results challenge the idea that changes in snowshoe hare foraging behaviour contribute to their cyclic dynamics. (Au)


Timing of reproduction by Red-tailed Hawks, Northern Goshawks and Great Horned Owls in the Kluane boreal forest of southwestern Yukon   /   Doyle, F.I.   Smith, J. [Supervisor]
Vancouver, B.C. : University of British Columbia, 2000.
3 microfiches : ill., 1 map ; 11 × 15 cm.
(Kluane Boreal Forest Ecosystem Project contribution, no. 163)
Appendices.
References.
Thesis (M.Sc.) - University of British Columbia, Vancouver, B.C., 2000.
Collation of print version: xiii, 141 leaves : ill., 1 map ; 28 cm.
ASTIS record 60786.
Languages: English
Libraries: BVAU

In this thesis, I examine the timing of breeding in 3 raptorial birds, red-tailed hawks (Buteo jamaicensis), the goshawks (Accipiter gentilis) and great-horned owls (Bubo virginianus). Specifically, I test Lack's 1954 theory that birds typically begin to breed such that the young bird's greatest demand for food will coincide later with the greatest abundance of available prey. Lack's theory predicts that birds which successfully match the timing of breeding to the peak in prey fledge more young that pairs which do not. This study was part of the larger Kluane Boreal Forest Ecosystem Project .... Detailed information on weather, prey density and timing of the peaks in prey availability was gathered annually. I examined the timing of breeding over 8 years (1989-1996) in an environment with both harsh winter weather and cyclic prey populations. The 3 species differ in both life history and morphology and yet share the same prey base for much of the year. These shared prey enable me to explore if and how the three species adjusted their breeding time to exploit the peaks in prey availability. The migrant red-tailed hawk bred every year and adjusted breeding to match the peak in prey availability. It bred early when its main prey, the Arctic ground squirrel, bred early thus ensuring that prey consumption needs of young red-tailed hawks corresponded with the synchronous emergence of young ground squirrels. In contrast, the resident great horned owl only bred when its main prey was abundant. Great horned owls have a long breeding period, and therefore bred before a peak in prey was available to match the peak in prey consumption demands of its young. The other resident, the goshawk, has a shorter breeding period than the owl, and bred such that a broad peak in available prey matched the peak consumption needs of its young. However, it is unclear if the goshawk adjusted breeding to match the predicted peak in prey, or if it had an average breeding time that corresponded tothe average breeding time of its preferred prey. Slight annual variation in the timing of breeding in the goshawk, like that of the other resident, the owl, may have been in response to fluctuations in winter prey density. These fluctuations in prey availability could through its influence on the raptors body condition, reduced the bird's ability to breed at the average time to which they have become adapted. Alternatively, goshawks may have adjusted their timing of breeding in response to a predicted later broad peak in prey, initiated by the increased availability of those prey during mating. Within a year, seasonal declines in the number of young that fledged were absent in the two resident species, but present for the migrant red-tailed hawk. Reduced fledging success in red-tailed hawks was attributed to attacks on the young by blackflies. Attacks from blackflies were so intense in 2 of the three years that all young hawks from 5 of the 12 intensively monitored nests died. These nests were all late and the young were <3 weeks of age at the time of blackfly emergence. Attacks by blackflies on young red-tailed hawks largely explained why the birds failed to attain maximum reproductive success every year, even though they matched peak needs by their young to the peak in prey availability. The resident goshawks and great horned owls only bred when they could do so successfully, while all red-tailed hawks bred every year. I propose that migration by the red-tailed hawk avoided the loss of body condition caused by low prey abundance in winter. However, the red-tailed hawk had a lower overall success rate, with only 25% of pairs fledging young in the least successful year. Over all years, when birds did breed, red-tailed hawks typically fledged 1-2 young and both goshawks and horned owls 2-3 young. (Au)


Compensatory growth of three herbaceous perennial species : the effects of clipping and nutrient availability   /   Hicks, S.   Turkington, R.
(Canadian journal of botany, v. 78, no. 6, June 2000, p. 759-767, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 165)
References.
ASTIS record 48374.
Languages: English
Web: doi:10.1139/cjb-78-6-759
Libraries: ACU

The continuum of responses model (CRM) and the growth rate model (GRM) make conflicting predictions about the effects of soil nutrient availability on the resilience of plants to herbivory. A factorial experiment was conducted in the understory of the boreal forest to examine the effects of fertilization and simulated herbivory on the rate and amount of regrowth of three herbaceous perennial species (Achillea millefolium L., Festuca altaica Trin., and Mertensia paniculata (Aiton) G. Don.). As clipping intensity increases various measures of plant performance decrease. Fertilization reduces the ability of clipped plants to compensate for biomass loss regardless of species and growth measure. Under natural soil fertility levels in this study, M. paniculata is more likely to compensate for leaf loss than A. millefolium and F. altaica. Contrary to the findings of previous field studies, the compensatory responses of the three species studied were most consistent with the predictions of the GRM. Plants in our study sites grow in nutrient-poor soils, whereas the majority of compensatory studies have been carried out on herbaceous or woody plants in temperate regions. Resources are generally more abundant in temperate zones than in boreal forest zones, and the GRM may be a better predictor of compensatory ability of plants growing in naturally nutrient-deficient soils. (Au)


Regulation of boreal forest understory vegetation : the roles of resources and herbivores   /   Dlott, F.   Turkington, R.
(Plant ecology, v.151, no. 2, Dec. 2000, p. 239-251, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 166)
Appendix.
References.
ASTIS record 53787.
Languages: English
Web: doi:10.1023/A:1026510727987

To understand inter-trophic linkages between components of the boreal forest understory vegetation, three hypotheses were tested: survival, growth and abundance of grasses and legumes were controlled by (i) resource availability alone, (ii) by herbivores alone, and (iii) by both resource availability and herbivores. The hypotheses were tested using three experimental treatments- fertilization, herbivore exclusion, and fertilization plus herbivore exclusion- in three areas having different densities of resident herbivores, mostly snowshoe hares and ground squirrels. The highest density of snowshoe hares is comparable to natural levels during peaks in the snowshoe hare cycle. As the density of herbivores increased so too did the level of response by the measured variables- survival, growth of transplants and leaf area index of established vegetation. In general, fertilization resulted in a decrease in survival and growth of transplants, and fences increased survival and growth; both responses were more noticeable at higher herbivore densities. Fertilizer and herbivore exclosure fences had only negligible effects on established grass and legume abundance at all hare densities. We have shown that some hypotheses of vegetation regulation are over-simplified because different species groups (i.e., grasses and legumes) are regulated by different factors, at different life history stages, and sometimes these factors act in opposing directions. We argue that during the increase phase and peak of the snowshoe hare cycle (high herbivore density), growth and survival of establishing plants is regulated by herbivores. During the decline and low phases of the snowshoe hare cycle herbivores will have little impact on early life stages, whereas the established, mature, vegetation will be resource-regulated. Because of the variability in responses to the same manipulations we may begin to understand which plant life history stages are most vulnerable to consumer and resource regulation, the magnitudes of these sources of regulation at each of these stages, and how these vary among species groups and types of environments. (Au)


Concurrent density dependence and independence in populations of arctic ground squirrels   /   Karels, T.J.   Boonstra, R.
(Nature, v.408, no.6811, 23 Nov. 2000, p. 460-463, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 170)
References.
ASTIS record 48543.
Languages: English
Web: doi:10.1038/35044064
Libraries: ACU

No population increases without limit. The processes that prevent this can operate in either a density-dependent way (acting with increasing severity to increase mortality rates or decrease reproductive rates as density increases), a density-independent way, or in both ways simultaneously. However, ecologists disagree for two main reasons about the relative roles and influences that density-dependent and density-independent processes have in determining population size. First, empirical studies showing both processes operating simultaneously are rare. Second, time-series analyses of long-term census data sometimes overestimate dependence. By using a density-perturbation experiment on arctic ground squirrels, we show concurrent density-dependent and density-independent declines in weaning rates, followed by density-dependent declines in overwinter survival during hibernation. These two processes result in strong, density-dependent convergence of experimentally increased populations to those of control populations that had been at low, stable levels. (Au)


Do nutrient availability and competition limit plant growth of herbaceous species in the boreal forest understory?   /   Arii, K.   Turkington, R.
(Arctic, antarctic, and alpine research, v. 34, no. 3, Aug. 2002, p. 251-261, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 171)
References.
ASTIS record 51835.
Languages: English
Web: doi:10.2307/1552482
Libraries: ACU

An experiment was conducted to investigate whether nutrient availability and competition limit aboveground growth of five herbaceous species in the boreal forest understory. The experiment involved adding fertilizer and removing neighbors of selected target individuals of five different species. Aboveground biomass and leaf number were measured as the response variables, and treatment effects were tested using ANOVA and ANCOVA. The five species showed variable responses to fertilizer addition with Achillea millefolium, Festuca altaica, and Mertensia paniculata showing significant increases. Lupinus arcticus had no response and there was a strong negative effect on survival of Anemone parviflora. Achillea was the only species that showed some growth limitation due to neighboring individuals for both biomass and leaf number; other species showed no response. (Au)


The effects of fertilization and herbivory on the herbaceous vegetation of the boreal forest in north-western Canada : a 10-year study   /   Turkington, R.   John, E.   Watson, S.   Seccombe-Hett, P.
(Journal of ecology, v. 90, no. 2, Apr. 2002, p. 325-337, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 172)
References.
ASTIS record 51907.
Languages: English
Web: doi:10.1046/j.1365-2745.2001.00666.x
Libraries: ACU

Summary: 1. The influence of fertilizer addition and mammalian herbivore exclosures (a 2 × 2 factorial design, with four replicates at each of two sites) on the cover, species composition and diversity of the understorey vegetation of the boreal forest in the south-western Yukon, Canada, were investigated from 1990 to 1999. This was done to test whether vegetation composition was controlled by resource level alone (bottom-up control), herbivory alone (top-down control), or by both (interactive control). 2. The density of the major herbivore, the snowshoe hare, varied 25-fold, declining from 148/km² in 1990 to 8/km² in 1994, and increasing to a second peak of 198/km² in 1998. 3. In control plots most species were remarkably constant in percent cover. After 10 years, most of the major species showed significant responses to fertilizer with four species increasing (Festuca altaica, Mertensia paniculata, Epilobium angustifolium, and Achillea millefolium), and three declining (Linnaea borealis, Lupinus arcticus, Arctostaphylos uva-ursi). Some species took up to 5 years before a response was detected. 4. Fertilization caused (i) a decline in the number of species, and species evenness in the community, (ii) a reduction in the proportion of woody species, and (iii) an increase in herbaceous dicotyledons and grasses. 5. The exclusion of herbivores had virtually no impact on the abundance of the vegetation or on species diversity, except in 1990-92 during a decline from a peak of 148 hares/km² to 29 hares/km². 6. These results suggest that the percentage cover and composition of herbaceous vegetation in the boreal forest are determined almost exclusively by the productivity of the site (bottom-up control) and that the activities of mammalian herbivores may be important only during peaks in hare population densities (interactive control). 7. Results were both species-specific and time-dependent, suggesting that long-term studies are needed to discriminate between long-term responses to treatments and transient phenomena. (Au)


Estimating snowshoe hare population density from pellet plots : a further evaluation   /   Krebs, C.J.   Boonstra, R.   Nams, V.   O'Donoghue, M.   Hodges, K.E.   Boutin, S.
(Canadian journal of zoology, v. 79, no. 1, Jan. 2001, p. 1-4, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 173)
References.
ASTIS record 53729.
Languages: English
Web: doi:10.1139/cjz-79-1-1
Libraries: ACU

We counted fecal pellets of snowshoe hares (Lepus americanus) once a year in 10 areas in the southwestern Yukon from 1987 to 1996. Pellets in eighty 0.155-m² quadrats were counted and cleared each June on all areas, and we correlated these counts with estimates of absolute hare density obtained by intensive mark-recapture methods in the same areas. There is a strong relationship between pellet counts and population density (r = 0.76), and we present a predictive log-log regression to quantify this relationship, which improves on our previously published 1987 regression, particularly at low hare densities. The precision of density estimates can be improved most easily by increasing the number of sets of quadrats in an area (one set = 80 plots), rather than increasing the number of plots counted within one set. The most important question remaining concerns the generality of this relationship for snowshoe hares living in other habitats in the eastern and southern portions of their geographic range. (Au)


Understanding the snowshoe hare cycle through large-scale field experiments   /   Boutin, S.   Krebs, C.J.   Boonstra, R.   Sinclair, A.R.E.   Hodges, K.E.
In: Population cycles : the case for trophic interactions / Edited by A. Berryman. - New York : Oxford University Press, 2002, ch. 4, p. 69-91, ill.
(Kluane Boreal Forest Ecosystem Project contribution, no. 174)
References.
ASTIS record 53797.
Languages: English
Libraries: ACU

The 10-year cycles of the snowshoe hare and lynx seen in Hudson's Bay fur returns represent a classic example of cyclic population dynamics. Hare cycles have been the subject of time series analysis (Stenseth et al. 1998), population modeling (Royama 1992), and field experimentation (Keith and Windberg 1978, Krebs et al. 1986, Murray et al. 1997). However, only two studies have monitored hare populations in detail over at least one full cycle. The first of these was conducted in central Alberta, Canada, by Lloyd Keith and co-workers, and provided a detailed description of the demographic machinery driving changes in hare numbers (Keith et al. 1977, Cary and Keith 1979, Keith et al. 1984). From this came the "Keith hypothesis" that hare cycles are driven by a sequential two-stage trophic interaction with hare declines initiated by winter food shortages and exacerbated by predator numerical responses that lag hare numbers by 1-2 years (Keith 1983, 1990). Predators force hares to low numbers and recovery does not occur until predator densities reach their lowest levels. The second long-term study of hare dynamics took place at Kluane Lake in the southwestern Yukon, Canada. The Kluane project began as an attempt to test the Keith hypothesis through single-factor manipulations of food supply and predation (Krebs et al. 1986, Sinclair et al. 1988, Smith et al. 1988). The first attempt failed to manipulate predators effectively, and plots containing food supplements were quickly overwhelmed by predators moving into the area. Consequently, the experiments failed to alter hare dynamics. Building on this experience, the second phase expanded the scale of experimental manipulations and developed an effective means of excluding predators from selected areas. The study also added an interaction treatment in which predators were excluded and food supplemented. These experiments were designed to test the roles of food supply, predation, and their potential interaction in the dynamics of snowshoe hares (Krebs et al. 1995). In this chapter we provide a synopsis of the key results obtained from these experiments and discuss how the results alter the current understanding of snowshoe hare dynamics. ... From this experimental work, we obtain the following demographic understanding of the snowshoe hare cycle. Obviously, the cyclic peak turns into a decline when recruitment no longer exceeds mortality. Our results suggest that this transition is due to the combined effect of reduced reproduction and increased mortality from predators. Furthermore, we did not find any evidence that malnutrition contributes to the population decline. Reducing the impact of mammalian predators resulted in increased adult survival, but does not appear to change reproductive output, and does not alter the cyclic pattern appreciably. Increasing food does not seem to affect either recruitment or mortality enough to change the cycle. The shift from the low phase to the increase phase requires reproduction to exceed mortality and, at least during this population cycle, this shift appeared to be primarily due to an increase in reproduction. This result is in contrast to the idea that delayed numerical responses of predators to hare density are necessary to "release" hares from the cyclic low. In theory, either reduced predation or increased reproduction would allow hares to enter the increase phase, and the actual balance may vary among cycles. ... (Au)


What drives the 10-year cycle of snowshoe hares?   /   Krebs, C.J.   Boonstra, R.   Boutin, S.   Sinclair, A.R.E.
(BioScience, v. 51, no. 1, Jan. 2001, p. 25-35, ill., maps)
(Kluane Boreal Forest Ecosystem Project contribution, no. 175)
References.
ASTIS record 53367.
Languages: English
Web: doi:10.1641/0006-3568(2001)051[0025:WDTYCO]2.0.CO;2
Libraries: ACU

In 1831 the manager of a Hudson's Bay Company post in northern Ontario wrote to the head office in London. The local Ojibway Indians were starving, he reported, because of a scarcity of “rabbits,” and they were unable to trap for furs because they spent all their time fishing for food (Winterhalder 1980). These shortages of so-called rabbits, which apparently occurred approximately every 10 years, are regularly mentioned in Canadian historical documents from the 18th and 19th centuries. Those rabbits were in fact snowshoe hares (Lepus americanus), and their 10-year cycle is one of the most intriguing features of the ecology of the boreal forest. Ten-year cycles were first analyzed quantitatively when wildlife biologists began to plot the fur trading records of Hudson's Bay Company during the early 1900s. The Hudson's Bay Company, established in 1671, kept meticulous records of the numbers of furs traded from different posts spread across Canada. The most famous time series drawn together from those records was that of Canada lynx (Elton and Nicholson 1942; Figure 1). The lynx is a specialist predator of snowshoe hares, and the rise and fall in lynx numbers mirrors, with a slight time lag, the rise and fall of snowshoe hare populations across the boreal region. The spectacular cycles of snowshoe hares and their predators have captured the attention of biologists as well as historians. These cycles are highlighted in virtually all ecology texts and are often cited as one of the few examples of Lotka-Volterra predator-prey equations, a simple model which shows never-ending oscillations in the numbers of predators and their prey. Cycles seem to violate the implicit assumption of many ecologists that there is a balance in nature, and anyone living in the boreal forest would be hard pressed to recognize a balance among the boom and bust in nature's economy. The challenge to biologists has been to understand the mechanisms behind these cycles, which has not been easy. One cycle lasts 10 years, and few PhD students or researchers wish to take 10 years to obtain n = 1. Fortunately, over the last 40 years ecologists working in Alberta, the Yukon Territory, and Alaska have put together an array of studies that have resolved most, but not all, of the enigmas behind these cycles (Keith 1990, Boutin et al. 1995). To understand any fluctuating population, one must first know in detail the mechanisms of changes in births, deaths, and movements that are the proximate causes of the changes in numbers. Before we describe these details, we should note that these 10-year hare cycles tend to occur in synchrony across broad regions. Indeed, hares across most of Canada and Alaska reached a peak in 1997-1999 during the most recent cycle. We explain the reasons behind this synchrony below, but let us note here that movements of hares cannot explain these population changes via immigration or emigration. Movements on a local level might be important, but at the regional level all populations rise and fall in unison. Population changes must be driven by changes in births and deaths. (Au)


Summer diet selection by snowshoe hares   /   Seccombe-Hett, P.   Krebs, C.J. [Supervisor]
Vancouver, B.C. : University of British Columbia, 1999.
vii, 157 p. : ill. ; 28 cm.
(Kluane Boreal Forest Ecosystem Project contribution, no. 176)
Thesis (M.Sc.) - University of British Columbia, 1999.
References.
Indexed from microfiche.
ASTIS record 60526.
Languages: English
Libraries: BVAU

The primary objective of this study was to identify the plant species included in the diets of male snowshoe hares (Lepus americanus) during the summer months. Snowshoe hare selection for and against each plant species was assessed by comparing the relative use and availability of each plant species. The secondary objective was to examine several hypotheses of what influenced the selection of those species individually and within an integrated modeling framework. Three hypotheses were examined i) Hares might select plants with high nutritional content (of energy or protein). ii) Hares might select plants to avoid or minimize deleterious plant secondary compounds (i.e. tannins and alkaloids). iii) Hares might select plants that minimize their risk of predation. The hare diet during the summer consists of five main plant species: Betula glandulosa, Festuca altaica, Lupinus arcticus, Salix spp. and Shepherdia canadensis, although a number of other species were occasionally included. Nutritionally, hares select for plant species with high protein content and avoid toxic effects from secondary compounds by ingesting a diverse diet. Hares are not consistently found associated with any particular vegetation types, although they prefer habitats with both a dense understory and an abundance of preferred food species. Although some support was generated for all of the hypotheses of diet selection, no single hypothesis explained all of the observed patterns of diet selection. A linear programming foraging model combined with optimization techniques was thus used to examine the interactions between the variables. Overall, the model is successful in integrating the conflicting hypotheses of hare foraging. It appears that hares change their diet selection in response to conflicting goals such as reproductive conditions and risk of predation. The model suggests that the interaction between plant protein and chemical defense compounds are the primary determinants of hare diet. (Au)


Climate and nutrient influences on the growth of white spruce trees in the boreal forests of the Yukon   /   Boonstra, R.   Desantis, L.   Krebs, C.J.   Hik, D.S.
(Climate research, v. 36, no. 2, Apr. 30, 2008, p. 123-130, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 178)
References.
ASTIS record 64458.
Languages: English
Web: doi:10.3354/cr00736

The boreal forests of North America are undergoing major changes because of the direct effects of global warming and increased CO2 levels. Plant production in the boreal forest is nutrient limited, and we examined how long-term fertilization affected growth of white spruce Picea glauca in the face of these major changes. We conducted a large-scale experiment by fertilizing two 1 km² stands of white spruce in the southwestern Yukon with commercial NPK fertilizer from 1987 to 1994. Tree growth was measured by the width of annual increments in 60 trees from each of 2 control and of 2 matched fertilized 1 km² sites for the period from 1977 to 1997 in a before, during, and after experimental design. Ring widths increased in both control and fertilized trees over this period as summer temperatures increased. Ring widths in fertilized trees increased from 9 to 48% over control trees during the years in which fertilizer was added, but immediately fell back to control levels from 1995 to 1997 at 1 site as soon as fertilization was stopped. In the long term, nitrogen in these forests may become tied up in shrubs, grasses, herbs, and fungi and not be available to the trees. There are 2 other possible explanations for this lack of sustained tree growth: first, the conversion of nitrogen into a form not readily available to spruce and, second, a spruce bark beetle outbreak that hit the southwestern Yukon during and after 1994 and affected 1 study site much more than the other. (Au)


Population limitation of the northern red-backed vole in the boreal forests of northern Canada   /   Boonstra, R.   Krebs, C.J.
(Journal of animal ecology, v. 75, no. 6, Nov. 2006, p.1269-1284, ill.)
(Kluane Boreal Forest Ecosystem Project contribution, no. 179)
References.
ASTIS record 61279.
Languages: English
Web: doi:10.1111/j.1365-2656.2006.01149.x
Libraries: ACU

1. Across the vast boreal forests of North America, no population cycles in Clethrionomys species occur. In Eurasia, by contrast, some Clethrionomys populations of the same species undergo regular 3-5-year cycles. We examined the effects of nutrients, food, competitors, predators and climate on population limitation in the northern red-backed vole (Clethrionomys rutilus Pallas) in the south-western Yukon to determine why this difference occurs. 2. From 1986 to 1996 we added food, reduced large mammal predators and excluded snowshoe hares (Lepus americanus Erxleben) from large plots and found that none of these manipulations affected red-backed vole abundance. Adding nutrients as nitrogen, phosphorus and potassium (NPK) fertilizer had a slight negative effect, probably acting through a reduction in dwarf shrub productivity caused by competition from grasses. 3. We monitored weasel populations directly through trapping and indirectly through snow tracking. Predation by these vole specialists was irrelevant as a limiting factor most of the time because voles in this area do not reach the densities needed to sustain weasel populations. Other boreal forest mammal and bird predators did not focus on red-backed voles. However, when red-backed vole populations increased in the forest and Microtus voles also increased in the meadows, weasel populations increased and may have temporarily depressed red-backed voles in winter. 4. We monitored one major potential food, white spruce seeds, but seed fall was not related to population changes in red-backed voles, even after mast years. 5. We assessed the impact of weather variables, and the average depth of the snow pack during winter (October-March) was correlated directly with vole demography, having both direct effects in that year and delayed effects in the following year. 6. Our long-term trapping data (1973-96) indicate that Clethrionomys populations fluctuated, with peaks following hare peaks by 2-3 years. 7. We propose that the key variable limiting these vole populations is overwinter survival, and this is a function of overwinter food from berries produced during the previous summer by dwarf shrubs. These shrubs may be stimulated by abundant moisture from winter snows or by periodic fertilization from large quantities of pellets produced at snowshoe hare peaks. (Au)


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