Canada lynx (Lynx canadensis) and snowshoe hares (Lepus americanus) form a keystone predator–prey cycle that has large impacts on the North American boreal forest vertebrate community. Snowshoe hares and lynx are both well-suited for snowy winters, but climate change-associated shifts in snow conditions could lower hare survival and alter cyclic dynamics. Using detailed monitoring of snowshoe hare cause-specific mortality, behaviour and prevailing weather, we demonstrate that hare mortality risk is strongly influenced by variation in snow conditions. Although predation risk from lynx was largely unaffected by snow conditions, coyote (Canis latrans) predation increased in shallow snow. Maximum snow depth in our study area has decreased 33% over the last two decades and predictions based on prolonged shallow snow indicate that future hare survival could resemble that seen during population declines. Our results indicate that climate change could disrupt cyclic dynamics in the boreal forest.
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Data available from the Dryad Digital Repository https://doi.org/10.5061/dryad.bzkh1896b.
The R code used to analyse the data and produce figures is available in the Dryad Digital Repository https://doi.org/10.5061/dryad.bzkh1896b.
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We thank the numerous field technicians who monitored hare survival and snow conditions throughout the study, as well as members of the Boutin Lab for comments on earlier versions of this manuscript. We also thank A. MacDonald and her family for long-term access to her trapline. We thank the Champagne and Aishihik, and Kluane First Nations, for supporting our work within their traditional territory. This work was supported by the Natural Sciences and Engineering Research Council of Canada, Northern Studies Training Programme, the University of Alberta Northern Research Award programme, the Association of Canadian Universities for Northern Studies, the Wildlife Conservation Society Canada, the W. Garfield Weston Foundation, the Killam Laureates programme, Government of Yukon and Earth Rangers.
The authors declare no competing interests.
Peer review information Nature Climate Change thanks Magnus Magnusson and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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Spring snowshoe hare density (± 95% Confidence Intervals) in the Kluane Lake region, Yukon over the last cycle. Hare density estimates are determined through mark-recapture as part of the Community Ecological Monitoring Project (CEMP; https://www.zoology.ubc.ca/~krebs/kluane.html), and densities displayed here come from trapping area 2 (blue) in the study area map (Supplementary Fig. 1). Shaded area represents the years where we monitored detailed survival and weather data throughout the entire winter (that is Dec-Mar).
Kaplan-Meier four-month survival curves (± 95% Confidence Intervals) for snowshoe hares in the Kluane Lake region, Yukon, across the three winters in which we monitored survival from December until March.
Modelled effect of snow depth (cm) on mortality risk in snowshoe hares. Mortality risk is based on coefficients from the best supported Cox-proportional hazards model, and shaded areas represent predicted response standard errors. The dotted line represents baseline risk for hares.
Difference in a) snow depth (cm), and b) sinking depth of the penetrometer (cm) at kill site locations for each predator species compared to the daily snow measurements taken on the date of the mortality.
Kaplan-Meier four-month survival curves (± 95% Confidence Intervals) for sub-adult (red) and adult (blue) snowshoe hares during the winter of a) 2015–16, b) 2016–17, c) 2017–18, and d) all years combined.
Extended Data Fig 6 Effect of snow conditions on age-specific mortality risk and foraging behaviour.
Modelled effect of the sinking depth of the penetrometer (cm) on mortality risk and daily foraging time for sub-adult (a, b) and adult (c, d) snowshoe hare at two different snow depths. Shaded areas represent predicted response standard errors and the dotted line represents baseline mortality risk (a, c) or the average time spent foraging per day in hours across the winter for sub-adults (b) and adults (d).
Canada lynx (blue, solid) and coyote (red, dashed) density in the Kluane lake region, Yukon, for each winter over the last snowshoe hare cycle. Densities in the region are determined each year based on track transects as part of the Community Ecological Monitoring Program (CEMP; https://www.zoology.ubc.ca/~krebs/kluane.html), where tracks are counted along a 25-km transect that traversed our study area, on days after fresh snowfalls while tracks were distinguishable (see Krebs et al. 26). Shaded area represents the years where we monitored detailed hare survival and weather data throughout the winter (that is Dec-Mar).
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Peers, M.J.L., Majchrzak, Y.N., Menzies, A.K. et al. Climate change increases predation risk for a keystone species of the boreal forest. Nat. Clim. Chang. (2020). https://doi.org/10.1038/s41558-020-00908-4