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Krebs C.J.,University of British Columbia | Bryant J.,University of Alaska Fairbanks | Kielland K.,University of Alaska Fairbanks | O'Donoghue M.,Yukon Fish and Wildlife Branch | And 14 more authors.
Canadian Journal of Zoology | Year: 2014

Snowshoe hares (Lepus americanus Erxleben, 1777) fluctuate in 9-10 year cycles throughout much of their North American range. These cycles show large variations in cyclic amplitude and we ask what factors could cause amplitude variation. We gathered data from 1976 to 2012 on hare numbers in the boreal forest of Alaska, Yukon, Northwest Territories, and northern British Columbia to describe the amplitude of hare fluctuations and to evaluate four possible causes. First, weather could cause variation in amplitude via hare reproduction or survival, but this mechanism does not fit our data. Second, bottom-up processes involving forest succession could explain amplitude variation through changes in winter forage availability, but succession is too slow a variable in our study areas. Third, plant defenses entrained by hare over-browsing in one cycle can produce variation in plant quality and quantity in subsequent cycles. A mathematical model suggests this is a possible explanation. Fourth, predator recovery following the cyclic low is inversely related to hare cyclic amplitude, and the existing data are consistent with this mechanism. A standardized regional monitoring program is needed to improve our understanding of cyclic amplitude variation in hares and the possible role of predators and winter foods in affecting amplitude. © 2014 National Research Council of Canada. All rights reserved.


Krebs C.J.,University of British Columbia | Kielland K.,University of Alaska Fairbanks | Bryant J.,University of Alaska Fairbanks | O'Donoghue M.,Yukon Fish and Wildlife Branch | And 13 more authors.
Canadian Journal of Zoology | Year: 2013

Snowshoe hares (Lepus americanus Erxleben, 1777) fluctuate in 9-10 year cycles throughout much of their North American range. Regional synchrony has been assumed to be the rule for these cycles, so that hare populations in virtually all of northwestern North America have been assumed to be in phase. We gathered qualitative and quantitative data on hare numbers and fur returns of Canada lynx (Lynx canadensis Kerr, 1792) in the boreal forest regions of Alaska, Yukon, Northwest Territories, and northern British Columbia to describe synchrony in the time window of 1970-2012 Broad-scale synchrony in lynx fur returns was strong from 1970 to about 1995 but then seemed to break down in different parts of this region. Hare populations at 20 sites in Alaska, the Yukon, and Northwest Territories showed peak populations that lagged by 1-4 years during the 1990s and 2000s cycles. The simplest hypothesis to explain these patterns of asynchrony in hare cycles is the movement of predators from British Columbia north into the Yukon and then east into the Northwest Territories and west into Alaska. A traveling wave of these cycles is clearly seen in the lynx fur returns from western Canada and Alaska from 1970 to 2009 One consequence of a failure of synchrony is that hare predators like Canada lynx and Great-horned Owls (Bubo virginianus (Gmelin, 1788)) can move from one adjacent area to the next within this region and survive long enough to prolong low densities in hare populations that have declined earlier.


Bowler B.,University of Canberra | Bowler B.,Khan Research Laboratories | Krebs C.,University of Canberra | Krebs C.,University of British Columbia | And 2 more authors.
Ecology | Year: 2014

We evaluated evidence of an effect of climate on the numerical response of a coyote (Canis latrans) population to their keystone prey, snowshoe hares (Lepus americanus), in a Canadian boreal forest. Six a priori hypotheses of the coyote numerical response were developed that postulated linear, nonlinear, additive, and interactive effects of prey and climate. Model selection procedures showed the North Atlantic Oscillation (NAO) had the strongest effect on the coyote numerical response via its interaction with snowshoe hare density, while other large-scale climate indices had very weak effects. For a given snowshoe hare density, a negative value of the NAO amplified the abundance of coyote and a positive NAO decreased coyote abundance. We hypothesize that the coyote numerical response is ultimately determined by the coyote functional response influenced by winter conditions determined by the NAO. © 2014 by the Ecological Society of America.


Hone J.,University of Canberra | Krebs C.J.,University of Canberra | Krebs C.J.,University of British Columbia | O'Donoghue M.,Yukon Fish and Wildlife Branch
Wildlife Research | Year: 2011

Context Predator dynamics may be related to prey abundance and influenced by environmental effects, such as climate. Predatorprey interactions may be represented by mechanistic models that comprise a deterministic skeleton with stochastic climatic forcing. Aims The aim of this study was to evaluate the effects of climate on predatorprey dynamics. The lynx and snowshoe hare predatorprey system in the Kluane region of the Yukon, Canada, is used as a case study. The specific hypothesis is that climate influences the relationship between lynx and hare abundance. Methods We evaluate 10 linear relationships between predator and prey abundance and effects of climate. We use data on lynx and snowshoe hare abundance over 21 years in the Yukon as the predatorprey system, and three alternative broad-scale climate indices: the winter North Atlantic Oscillation (NAO), the Pacific North American (PNA) index and the North Pacific index (NPI). Key results There was more support, as assessed by Akaike weights (i=0.600), evidence ratio (=4.73) and R 2 (=0.77) for a model of predator (lynx) and prior prey (hare) abundance with an effect of prior climate (winter NAO) when combined in a multiplicative, rather than in an additive, manner. The results infer that climate changes the amplitude of the lynx cycle with lower predator (lynx) abundance with positive values of winter NAO for a given hare density. Conclusions The study provides evidence that predatorprey dynamics are related to climate in an interactive manner. The ecological mechanism for the interactive effect is not clear, and alternative hypotheses are proposed for future evaluation. Implications The study implies that changes in climate may alter predatorprey relationships. © 2011 CSIRO.

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