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Data from: Climate change increases predation risk for a keystone species of the boreal forest
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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Senescence and the stress axis in male ground squirrels
Boonstra, Rudy; Delehanty, Brendan — 2023-07-26 <p>A critical time in the life of a male occurs at reproduction when his behavior, physiology, and resources must be brought to bear for the central purpose of his life. We ask whether reproduction results in dysfunction of the stress axis, is linked to life history, and causes senescence. We assessed if deterioration in the axis underlies variation in reproductive lifespan in males of 5 species of North American ground squirrels whose life history varies from near semelparity to iteroparity. The most stressful and energy-demanding time occurs in spring during the intense 2–3 week breeding competition just after arousal from hibernation. We compared their stress axis functioning before and after the mating period using a hormonal challenge protocol. We found no evidence of stress axis dysfunction nor was there a relationship between reproductive lifespan and stress axis functional deterioration.  Moreover, there was no consistent relationship between free cortisol levels and downstream measures. Thus, stress axis function was not traded off to promote reproduction and conclude that it is a pre-requisite for life. Hence, it functions as a constraint and does not undergo senescence.</p>
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Data from: Vertebrate scavenging dynamics differ between carnivore and herbivore carcasses in the northern boreal forest
Peers, Michael; Konkolics, Sean; Majchrzak, Yasmine; Menzies, Allyson; Studd, Emily; Boonstra, Rudy; Boutin, Stan; Lamb, Clayton — 2021-07-23 <p>Vertebrate scavenging can impact food web dynamics, but our understanding of this process stems predominantly from monitoring herbivore carrion and extrapolating results across carcass types. Recent evidence suggests carnivores may avoid intraguild scavenging to reduce parasite transmission. If this behavior is widespread across diverse ecosystems, estimation of nutrient cycling and community scavenging rates are likely biased to a currently unknown degree. We examined whether the time to initiate scavenging, carcass persistence, or the richness of species scavenging in the boreal forest of Yukon, Canada, differed between carnivore and herbivore carcasses. Vertebrates took longer to initiate scavenging on carnivore carcasses (3.2 days) relative to herbivore carcasses (1.1 days), and carnivore carcasses persisted on the landscape for over a month longer (48.4 days and 5.5 days, respectively). The longer persistence times were due to the reduction in scavenging by carnivores such as Canada lynx (<i>Lynx canadensis</i>). Decreased scavenging was caused by changes in the propensity to consume carnivore carrion, as the number of species detecting a carcass within the first week did not differ between carnivore and herbivore carcasses. These results have ramifications for our understanding of nutrient cycling and food web dynamics in the boreal forest, and provide further support that carcass type should be included in future studies.</p>
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Data from: Managing anabolic steroids in pre-hibernating Arctic ground squirrels: obtaining their benefits and avoiding their costs
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Boonstra, Rudy; Mo, Kaiguo; Monks, Douglas Ashley — 2014-10-17 Androgens have benefits, such as promoting muscle growth, but also significant costs, including suppression of immune function. In many species, these trade-offs in androgen action are reflected in regulated androgen production, which is typically highest only in reproductive males. However, all non-reproductive Arctic ground squirrels, irrespective of age and sex, have high levels of androgens prior to hibernating at sub-zero temperatures. Androgens appear to be required to make muscle in summer, which, together with lipid, is then catabolized during overwinter. By contrast, most hibernating mammals catabolize only lipid. We tested the hypothesis that androgen action is selectively enhanced in Arctic ground squirrel muscle because of an upregulation of androgen receptors (ARs). Using Western blot analysis, we found that Arctic ground squirrels have AR in skeletal muscle more than four times that of Columbian ground squirrels, a related southern species that overwinters at approximately 0°C and has low pre-hibernation androgen levels. By contrast, AR in lymph nodes was equivalent in both species. Brain AR was also modestly but significantly increased in Arctic ground squirrel relative to Columbian ground squirrel. These results are consistent with the hypothesis that tissue-specific AR regulation prior to hibernation provides a mechanism whereby Arctic ground squirrels obtain the life-history benefits and mitigate the costs associated with high androgen production.
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Data from: Prey availability and ambient temperature influence carrion persistence in the boreal forest
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Peers, Michael; Konkolics, Sean; Lamb, Clayton; Majchrzak, Yasmine; Menzies, Allyson; Studd, Emily; Boonstra, Rudy; Kenney, Alice; Krebs, Charles; Martinig, April Robin; McCulloch, Baily; Silva, Joseph; Garland, Laura; Boutin, Stan — 2020-10-09 <p>1. Scavenging by vertebrates can have important impacts on food web stability and persistence, and can alter the distribution of nutrients throughout the landscape. However, scavenging communities have been understudied in most regions around the globe, and we lack understanding of the biotic drivers of vertebrate scavenging dynamics.</p> <p>2. In this paper, we examined how changes in prey density and carrion biomass caused by population cycles of a primary prey species, the snowshoe hare (<i>Lepus americanus</i>), influence scavenging communities in the northern boreal forest. We further examined the impact of habitat and temperature on scavenging dynamics.</p> <p>3. We monitored the persistence time, time until first scavenger, and number of species scavenging experimentally-placed hare carcasses over four consecutive years in the southwestern Yukon. We simultaneously monitored hare density and carrion biomass to examine their influence relative to temperature, habitat, and seasonal effects. For the primary scavengers, we developed species-specific scavenging models to determine variation on the effects of these factors across species, and determine which species may be driving temporal patterns in the entire community.</p> <p>4. We found that the efficiency of the scavenging community was affected by hare density, with carcass persistence decreasing when snowshoe hare densities declined, mainly due to increased scavenging rates by Canada lynx (<i>Lynx canadensis</i>). However, prey density did not influence the number of species scavenging a given carcass, suggesting prey abundance affects carrion recycling but not necessarily the number of connections in the food web. In addition, scavenging rates increased in warmer temperatures, and there were strong seasonal effects on the richness of the vertebrate scavenging community.</p> <p>5. Our results demonstrate that vertebrate scavenging communities are sensitive to changes in species’ demography and environmental change, and that future assessments of food web dynamics should consider links established through scavenging.</p>
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Data from: Stress and the microbiome: linking glucocorticoids to bacterial community dynamics in wild red squirrels
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Stothart, Mason R.; Bobbie, Colleen B.; Schulte-Hostedde, Albrecht I.; Boonstra, Rudy; Palme, Rupert; Mykytczuk, Nadia C. S.; Newman, Amy E. M. — 2015-12-04 Bacterial diversity within animals is emerging as an essential component of health, but it is unknown how stress may influence the microbiome. We quantify a proximate link between the oral microbiome and hypothalamic–pituitary–adrenal (HPA) axis activity using faecal glucocorticoid metabolites (FGM) in wild red squirrels (Tamiasciurus hudsonicus). Not only was bacterial diversity lower at higher levels of FGM, but also between capture periods a change in bacterial relative abundance was related to an increase in FGM. These linkages between the HPA axis and microbiome communities represent a powerful capacity for stress to have multi-dimensional effects on health.
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Data from: Using experimentation to understand the 10-year snowshoe hare cycle in the boreal forest of North America
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Krebs, Charles; Boonstra, Rudy; Boutin, Stan; Krebs, Charles J. — 2018-06-07 1. Population cycles have long fascinated ecologists from the time of Charles Elton in the 1920s. The discovery of large population fluctuations in undisturbed ecosystems challenged the idea that pristine nature was in a state of balance. The 10-year cycle of snowshoe hares (Lepus americanus Erxleben) across the boreal forests of Canada and Alaska is a classic cycle, recognized by fur traders for more than 300 years. 2. Since the 1930s ecologists have investigated the mechanisms that might cause these cycles. Proposed causal mechanisms have varied from sunspots to food supplies, parasites, diseases, predation, and social behaviour. Both the birth rate and the death rate change dramatically over the cycle. Social behaviour was eliminated as a possible cause because snowshoe hares are not territorial and do not commit infanticide. 3. Since the 1960s large-scale manipulative experiments have been used to discover the major limiting factors. Food supply and predation quickly became recognized as potential key factors causing the cycle. Experiments adding food and restricting predator access to field populations have been decisive in pinpointing predation as the key mechanism causing these fluctuations. 4. The immediate cause of death of most snowshoe hares is predation by a variety of predators, including the Canada lynx (Lynx canadensis Kerr). The collapse in the reproductive rate is not due to food shortage as was originally thought, but is a result of chronic stress from predator chases. 5. Five major issues remain unresolved. First, what is the nature of the predator-induced memory that results in the prolonged low phase of the cycle? Second, why do hare cycles form a travelling wave, starting in the centre of the boreal forest in Saskatchewan and travelling across western Canada and Alaska? Third, why does the amplitude of the cycle vary greatly from one cycle to the next in the same area? Fourth, do the same mechanisms of population limitation apply to snowshoe hares in eastern North American or in similar ecosystems across Siberia? Finally, what effect will climatic warming have on all the above issues? The answers to these questions remain for future generations of biologists to determine.

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(auteur : Boonstra, Rudy)

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