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Peers, Michael; Majchrzak, Yasmine; Menzies, Allyson; Studd, Emily; Bastille-Rousseau, Guillaume; Boonstra, Rudy; Humphries, Murray; Jung, Thomas; Kenney, Alice; Krebs, Charles; Murray, Dennis; Boutin, Stan 2021-06-16 <p style="text-indent:36.0pt;">Canada lynx (<i>Lynx canadensis</i>) and snowshoe hares (<i>Lepus americanus</i>) 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 (<i>Canis latrans</i>) 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 future hare survival could resemble that seen during population declines. Our results indicate that climate change could disrupt cyclic dynamics in the boreal forest.</p>
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Menzies, Allyson; Studd, Emily; Majchrzak, Yasmine; Peers, Michael; Boutin, Stan; Dantzer, Ben; Lane, Jeffrey; McAdam, Andrew; Humphries, Murray 2020-07-31 <ol> <li style="margin-bottom:12px;">Organisms survive environmental variation by combining homeostatic regulation of critical states with allostatic variation of other traits, and species differences in these responses can contribute to coexistence in temporally-variable environments.</li> <li style="margin-bottom:12px;">In this paper, we simultaneously record variation in three functional traits – body temperature (Tb), heart rate, and activity - in relation to three forms of environmental variation – air temperature (Ta), photoperiod, and experimentally-manipulated resource levels – in free-ranging snowshoe hares and North American red squirrels to characterize distinctions in homeotherm responses to the extreme conditions of northern boreal winters.</li> <li style="margin-bottom:12px;">Hares and squirrels differed in the level and precision of Tb regulation, but also in the allostatic pathways necessary to maintain thermal homeostasis. Hares demonstrated a stronger metabolic pathway (through heart rate variation reflective of the thermogenesis), while squirrels demonstrated a stronger behavioral pathway (through activity variation that minimizes cold exposure).</li> <li style="margin-bottom:12px;">As intermediate-sized, winter-active homeotherms, hares and squirrels share many functional attributes, yet, through the integrated monitoring of multiple functional traits in response to shared environmental variation, our study reveals many pairwise species differences in homeostatic and allostatic traits, that both define and are defined by the natural history, functional niches, and coexistence of sympatric species.</li> </ol> https://creativecommons.org/publicdomain/zero/1.0/