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The estimation of energy expenditure is key to resolve ecological questions and conservation strategies. The puma ( Puma concolor (Linnaeus, 1771)) has been the subject of several efforts to measure the daily energy expenditure (DEE). Most of the estimations have been made using movement or activity models that have been questioned because of discrepancies with kill rates. This study looks at one movement model estimation and validates it using doubly labeled water (DLW), which can also account for energy expenditures beyond those associated with activity. We captured six pumas (51.5 ± 9.9 (SD) kg) during the winter in Colorado that were GPS collared and injected with DLW for an approximately 3-week trial. We found that DEE obtained from the DLW (14.5 ± 6.1 MJ·day−1) did not differ from that estimated using the movement model or from the predicted allometric equation based on DLW studies on other mammals. Decreasing air temperature and increasing daily distance movement were correlated with increasing DEE for monitored pumas. Both DLW and movement models provide a reasonable proxy to estimate DEE at the population level but exhibit low precision in estimating individual values for free-ranging puma.

Winter is a costly time for animals, requiring individuals to adapt to increased energetic costs and reduced resources. Porcupines ( Erethizon dorsatum (Linnaeus, 1758)) confront winter by storing and catabolizing somatic stores. Increasing temperatures and attenuated snow conditions due to climate change increase porcupine survival, but impacts of greater weather variability have not been explored. In April of 2018, an anomalously heavy and late snowstorm occurred at our long-term study site in central Wisconsin followed by multiple mortalities among adult porcupines. We assessed cause of mortality and determined nutritional condition by extracting bone marrow and quantifying lipid content. Porcupines that died following the snow event had lower fat stores than the fall 2019 group and likely died of starvation. We estimated survival of female porcupines during the winters of 2012 and 2015–2018 to assess the effects of snow conditions and nutritional condition on survival. Survival declined with increased snow depth but increased with improved nutritional condition. The mass starvation event we observed in 2018 appeared to have resulted from deep snow increasing locomotive costs and reducing nutritional condition. As climate change increases the frequency of extreme weather events, including extreme snowfalls, we predict that the frequency of such clustered mortalities will increase.

To minimize competitive overlap, carnivores modify one of their critical niche axes: space, time, or resources. However, we currently lack rules for how carnivore communities operate in human-dominated landscapes. We simultaneously quantified overlap in the critical niche axes of a simple carnivore community-an apex carnivore (

In seasonal environments, the winter months can drive the structure and dynamics of vertebrate communities. Most ecological studies have focused on species above the snow, overlooking those within the subnivium (below-snow environment). The Great Lakes region of North America is characterized by seasonal snow cover and a diverse assemblage of small mammals, both of which are changing rapidly in response to a changing climate. To study the seasonal dynamics of small mammals, we sampled communities in three forest types (hardwood, hemlock-cedar, and spruce bog) in summer and winter over 2 years. We hypothesized that seasonal differences in communities would be moderated by forest structure in summer and snow in winter. We assessed community dominance via species diversity and the abundances of deer mice (Peromyscus maniculatus), white-footed mice (P. leucopus), and southern red-backed voles (Myodes gapperi). We estimated a Community Temperature Index (CTI; a metric of the balance between warm- and cold-adapted species in a community) and tested seasonal drivers of CTI. Species diversity was highest in spruce bogs in winter due to increased species evenness, but diversity was consistent year-round in hardwood and hemlock-cedar forests due to unchanging species dominance. Spruce bogs supported the coldest CTI in summer, but CTIs converged across forest types in winter. In summer, forest structure drove CTI; in winter, colder CTIs were associated with deeper snow and a warmer subnivium. Our work reveals that snow is a critical habitat and filter for cold-adapted species that ultimately structures small mammal communities. Given rapid changes in snow conditions due to climate change, we predict continued range contractions for subnivium-adapted species.

Climate change is creating hotter, drier, and more extreme weather. Weather anomalies such as extended drought along the Pacific Coast of North America are redefining ecosystems. In the Sierra Nevada mountains of California, an isolated, distinct and federally endangered population of fishers (Pekania pennanti) currently faces multiple threats. Severe drought, tree mortality, and megafires are reshaping the landscape in the southern Sierra with largely unknown effects on fisher ecology and conservation. Using hair collected during long-term population monitoring, we analyzed stable isotopes to quantify the diets of fishers before and after drought, and explored how habitat quality mediated the effect of drought on fisher diet. For the core population of fishers which occupy the northern and western portions of this region, their isotopic niche declined both in drought and in lower-quality habitats. Regardless of drought or habitat conditions, the summer diet of fishers here was dominated by fungi (47%), while little vertebrate mass (14%) was consumed. However, drought and habitat did influence consumption of plants and insects; fishers consumed more insects and less plants in drought conditions and in poorer habitat. In contrast, at the perennially dry, high-altitude Kern Plateau at the southeastern extent of their range, fishers predominantly consumed vertebrates (59%). Fishers show great plasticity in their diet, but the means and capacity for this flexibility is poorly understood. Retaining atypical diet items, notably fungi, and a diversity of forage in the Sierra Nevada could help to buffer the negative fitness costs from rapid environmental change for this endangered species.

Species reintroductions are successful when established populations maintain both demographic stability and genetic diversity. Such a result may be obtained by ensuring both structural habitat connectivity and genetic connectivity among reintroduced and remnant populations. Nevertheless, prezygotic barriers such as assortative mating can prevent the flow of genetic material between populations, even when migration between populations is high. Limited gene flow may be particularly relevant for reintroductions that were sourced either from captive-bred populations or from disparate locations in the wild. American martens (Martes americana) have been reintroduced repeatedly in the Upper Midwestern United States in an effort to establish self-sustaining populations. We quantified levels of genetic diversity within and spatial genetic variance among four marten populations during two time periods separated by 10 years. Spatially informed and naïve discriminant analysis of principal components were used to assign individuals to populations. Results indicate that heterozygosity declined and inbreeding coefficients increased between the two collection periods, while genetic structure among populations also increased. Data are consistent with assortative mating contributing to reapportioning of genetic variation. Population assignment tests show that migration among populations is apparent, but admixture (based on cluster membership probabilities) is low and declined over time. Specifically, martens may be successfully dispersing between populations but a lack of admixture indicates a lack of reproductive contributions to genetic diversity by migrants. Because marten reintroductions in this region are well-documented and well-monitored, lessons can be derived from results to inform future reintroductions. We encourage a careful balance of supplementing genetic diversity via augmentation while avoiding translocation of animals from disparate populations that may result in reproductive isolation of migrants. In combination with the maintenance of a functionally connected landscape, this strategy would maximize the likelihood of a successful reintroduction in terms both of demography and genetics.

Competition structures ecological communities. In carnivorans, competitive interactions are disproportionately costly to subordinate carnivores who must account for the risk of interspecific killing when foraging. Accordingly, missed opportunity costs for meso-carnivores imposed by risk can benefit the smallest-bodied competitors. However, the extent to which the risk perpetuates into spatial partitioning in hierarchically structured communities remains unknown. To determine how risk-avoidance behaviors shape the space-use of carnivore communities, we studied a simple community of carnivores in northern Patagonia, Argentina: pumas (Puma concolor; an apex carnivore), culpeo foxes (Lycalopex culpaeus; a meso-carnivore), and chilla foxes (Lycalopex griseus; a small carnivore). We used multi-species occupancy models to quantify the space use within the carnivore community and giving-up densities to understand the behaviors that structure space use. Notably, we applied an analytical framework that tests whether the actual or perceived risk of predation most strongly influences the space use of subordinate carnivores although accounting for their foraging and vigilance behaviors. We found that there was a dominance hierarchy from the apex carnivore through the meso-carnivore to the subordinate small carnivore, which was reflected in space. Although both meso- and small carnivores exhibited similar predator avoidance behavioral responses to apex carnivores, the habitat associations of apex carnivores only altered meso-carnivore space use. The biases in risk management we observed for meso-carnivores likely translates into stable co-existence of this community of competing carnivores. We believe our analytical framework can be extended to other communities to quantify the spatial-behavioral tradeoffs of risk.

Ecological heterogeneity promotes species persistence and diversity. Environmental change has, however, eroded patterns of heterogeneity globally, stifling species recovery. To test the effects of seasonal heterogeneity on a reintroduced carnivore, American martens ( Martes americana ), we compared metrics of local and season-specific heterogeneity to traditional forest metrics on the survival of 242 individuals across 8 years and predicted a survival landscape for 13 reintroduction sites. We found that heterogeneity—created by forest structure in the growing season and snow in the winter—improved survival and outperformed traditional forest metrics. Spatial variation in heterogeneity created a distinct survival landscape, but seasonal change in heterogeneity generated temporal discordance. All translocation sites possessed high forest heterogeneity but there were greater differences in winter heterogeneity; recovery sites with the poorest snow conditions had the lowest viability. Our work links heterogeneity across seasons to fitness and suggests that management strategies that increase seasonal aspects of heterogeneity may help to recover other sensitive species to continuing environmental change.

The effects of predation risk on prey populations have been studied extensively; yet, how risk is manifested in a trophically linked guild-scavengers-has been overlooked. Risk could be particularly consequential for obligate scavengers that are vulnerable while foraging and rely on carrion provisioned by, and shared with, apex predators. We investigated whether Andean condors (Vultur gryphus) respond to predation risk in a landscape where the main source of carrion are camelids killed by pumas (Puma concolor). We hypothesized that condors would exhibit different behavioral responses to predation risk while they search, encounter, and exploit carrion. We explored condor habitat selection while flying by tracking nine birds with satellite transmitters and monitored via camera traps 41 natural carcasses and 25 experimental carrion stations. We found that condors searched for carrion in areas with a high probability of occurrence of puma kills. However, condors avoided exploiting carrion in areas featuring tall vegetation and steep slopes-selected by pumas to stalk prey-suggesting that condors manage risk primarily through the identification of safe foraging sites prior to landing. Our finding that condors avoided foraging near stalking cover for pumas highlights the importance of risk effects beyond predator-prey interactions, particularly for obligate scavengers.

The subnivium is the seasonal microhabitat at the snow–ground interface and serves as a refuge for a diversity of species. Increasingly warmer winters are disrupting the continuity of snow cover, and likely the stability of the subnivium. To examine how the extent and duration of this sensitive and widespread below‐snow habitat will shift under warming winters, we deployed fully automated winter greenhouses across latitudinal and land‐cover gradients to monitor subnivium conditions under different climate‐change scenarios and predicted subnivium occurrence across the Great Lakes region. In a +3°C warming scenario, we found little change in subnivium extent or duration, whereas a +5°C scenario produced widespread and marked reductions in both extent (loss of 200,000 km², a 45% decline) and duration (>1 month decline). Although the subnivium appears resilient to moderate future warming, we predict abrupt and extensive changes in response to increased winter warming, which will have sweeping ecological and environmental consequences in high‐latitude ecosystems.

Characterizing animal space-use and resource selection is central to effective conservation. In seasonally variable systems, animals may alter space-use to minimize risk, mediate physiological costs, and maintain access to resources. However, it is often unclear which environmental features influence space-use across seasons, and whether resource selection of non-migratory animals varies in seasonally snow-covered environments. We quantified space-use and scale-dependent resource selection of Pacific martens (Martes caurina) in northern California to evaluate the relative influence of abiotic (e.g., topography, weather) and biotic (e.g., forest structure) covariates on spatial ecology of martens in ecologically distinct seasons (i.e., snow-covered, snow-free). We obtained fine-scale location data from GPS-collared martens (n = 26) in the Cascade and Sierra Nevada mountain ranges in California, USA. We incorporated spatially explicit weather, topographic, and forest structure data in a scale-optimized, seasonal resource selection function framework to determine the relative importance of abiotic and biotic conditions during snow-covered and snow-free periods. During snow-free periods, martens selected for features associated with complex forest structure, including increasing stem basal area. Conversely, space-use was associated with dense forest structure and topographic features in snow-covered periods. Though the relative influence of abiotic and biotic covariates on resource selection varied by season, the scale at which these variables best explained space-use did not. Our results highlight seasonality and scale-dependence of resource selection by martens and emphasize the importance of understanding spatio-temporal responses of free-ranging animals to landscape heterogeneity. We suggest behavioral or ecological requirements that differ by season and scale may influence space-use and resource selection patterns, and, consequently, can inform conservation actions.

Habitat loss is the leading cause of species extinctions and is especially detrimental to habitat specialists. Freshwater turtles require specific habitat types at different points in their life cycle; notably, the loss of nesting habitat has led to increased nest depredation and adult mortality. In response, conservationists have implemented nest protection and habitat restoration programs to recover declining populations. Although assumed to increase nest survival, effectiveness of these methods has not been rigorously quantified. We located Wood Turtle (Glyptemys insculpta (Le Conte, 1830)) nests in Wisconsin (USA) and conducted two analyses — logistic regression and logistic exposure — to investigate the influence of management actions and environmental factors on nest survival. The depredation rate decreased by 47% for protected nests and declined as nests aged; the success rate increased by 28% for protected nests and increased for nests in areas with fewer roads. We found high annual variation in success, and although weather variables were not predictive, likely due to their coarse scale, we posit that this inter-annual variation was driven by variation in weather conditions. Our results suggest that nest protection is effective at increasing nest survival, but future efforts should span multiple years to account for the effects of annual variation in environmental conditions.

Winter climate warming is rapidly leading to changes in snow depth and soil temperatures across mid- and high-latitude ecosystems, with important implications for survival and distribution of species that overwinter beneath the snow. Amphibians are a particularly vulnerable group to winter climate change because of the tight coupling between their body temperature and metabolic rate. Here, we used a mechanistic microclimate model coupled to an animal biophysics model to predict the spatially explicit effects of future climate change on the wintering energetics of a freeze-tolerant amphibian, the Wood Frog (Lithobates sylvaticus), across its distributional range in the eastern United States. Our below-the-snow microclimate simulations were driven by dynamically downscaled climate projections from a regional climate model coupled to a one-dimensional model of the Laurentian Great Lakes. We found that warming soil temperatures and decreasing winter length have opposing effects on Wood Frog winter energy requirements, leading to geographically heterogeneous implications for Wood Frogs. While energy expenditures and peak body ice content were predicted to decline in Wood Frogs across most of our study region, we identified an area of heightened energetic risk in the northwestern part of the Great Lakes region where energy requirements were predicted to increase. Because Wood Frogs rely on body stores acquired in fall to fuel winter survival and spring breeding, increased winter energy requirements have the potential to impact local survival and reproduction. Given the geographically variable and intertwined drivers of future under-snow conditions (e.g., declining snow depths, rising air temperatures, shortening winters), spatially explicit assessments of species energetics and risk will be important to understanding the vulnerability of subnivium-adapted species.

Interspecific competition can limit species distributions unless competitors partition niche space to enable coexistence. Landscape heterogeneity can facilitate niche partitioning and enable coexistence, but land-use change is restructuring terrestrial ecosystems globally with unknown consequences for species interactions. We tested the relationship between landscape heterogeneity and carnivore co-occurrence in natural and human-dominated ecosystems to assess the landscape-mediated impacts of anthropogenic change on coexistence. We used boosted regression trees to model the distributions and co-occurrence of two competing forest carnivores, American martens and fishers, at two contrasting sites in the Great Lakes region, USA: a “natural” site largely devoid of human impacts and a “human-dominated” site with substantial development and a history of land-use change. We assessed the importance of climate and habitat variables for each species, measured spatial niche overlap, and quantified co-occurrence as a function of compositional (patch richness), configurational (landscape shape), and topographical (elevation range) heterogeneity per site. We observed significant differences in the effect of heterogeneity on co-occurrence between sites. The natural landscape exhibited little niche overlap and co-occurrence had a significant, positive relationship with heterogeneity. Conversely, the human-dominated site exhibited high niche overlap with variable effects of heterogeneity on co-occurrence. Elevation, snowpack, and development had strong, contrasting effects on marten and fisher distributions, suggesting that differential use of habitat and anthropogenic features facilitates coexistence. Heterogeneity can facilitate coexistence, but too much may undermine carnivore coexistence in human-dominated landscapes where habitat and space are limited. Moreover, future climate change will likely erode niche partitioning among martens and fishers, with particularly strong consequences for coexistence in human-dominated landscapes and at range boundaries.

The relationship between body size and latitude has been the focus of dozens of studies across many species. However, results of testing Bergmann’s rule — that organisms in colder climates or at higher latitudes possess larger body sizes — have been inconsistent across studies. We investigated whether snowshoe hares (Lepus americanus Erxleben, 1777) follow Bergmann’s rule by investigating differences in body mass using data from six published studies and from data of 755 individual hares captured from 10 populations across North America covering 26° of north latitude. We also explored alternative hypotheses related to variation in hare body mass, including winter severity, length of growing season, elevation, and snow depth. We found body mass of hares varied throughout their range, but the drivers of body mass differed based on geographic location. In northern populations, females followed Bergmann’s rule, whereas males did not. In northern populations, male mass was related to mean snow depth. In contrast, in southern populations, body mass of both sexes was related to length of the growing season. These differences likely represent variation in the drivers of selection. Specifically, in the north, a large body size is beneficial to conserve heat because of low winter temperatures, whereas in the south, it is likely due to increased food supply associated with longer growing seasons.

Disease outbreaks induced by humans increasingly threaten wildlife communities worldwide. Like predators, pathogens can be key top-down forces in ecosystems, initiating trophic cascades that may alter food webs. An outbreak of mange in a remote Andean protected area caused a dramatic population decline in a mammalian herbivore (the vicuña), creating conditions to test the cascading effects of disease on the ecological community. By comparing a suite of ecological measurements to pre-disease baseline records, we demonstrate that mange restructured tightly linked trophic interactions previously driven by a mammalian predator (the puma). Following the mange outbreak, scavenger (Andean condor) occurrence in the ecosystem declined sharply and plant biomass and cover increased dramatically in predation refuges where herbivory was historically concentrated. The evidence shows that a disease-induced trophic cascade, mediated by vicuña density, could supplant the predator-induced trophic cascade, mediated by vicuña behaviour, thereby transforming the Andean ecosystem.

Rapid environmental change is reshaping ecosystems and driving species loss globally. Carnivore populations have declined and retracted rapidly and have been the target of numerous translocation projects. Success, however, is complicated when these efforts occur in novel ecosystems. Identifying refuges, locations that are resistant to environmental change, within a translocation framework should improve population recovery and persistence. American martens (Martes americana) are the most frequently translocated carnivore in North America. As elsewhere, martens were extirpated across much of the Great Lakes region by the 1930s and, despite multiple translocations beginning in the 1950s, martens remain of regional conservation concern. Surprisingly, martens were rediscovered in 2014 on the Apostle Islands of Lake Superior after a putative absence of >40 yr. To identify the source of martens to the islands and understand connectivity of the reintroduction network, we collected genetic data on martens from the archipelago and from all regional reintroduction sites. In total, we genotyped 483 individual martens, 43 of which inhabited the Apostle Islands (densities 0.42-1.46 km-2 ). Coalescent analyses supported the contemporary recolonization of the Apostle Islands with progenitors likely originating from Michigan, which were sourced from Ontario. We also identified movements by a first-order relative between the Apostle Islands and the recovery network. We detected some regional gene flow, but in an unexpected direction: individuals moving from the islands to the mainland. Our findings suggest that the Apostle Islands were naturally recolonized by progeny of translocated individuals and now act as a source back to the reintroduction sites on the mainland. We suggest that the Apostle Islands, given its protection from disturbance, complex forest structure, and reduced carnivore competition, will act as a potential refuge for marten along their trailing range boundary and a central node for regional recovery. Our work reveals that translocations, even those occurring along southern range boundaries, can create recovery networks that function like natural metapopulations. Identifying refuges, locations that are resistant to environmental change, within these recovery networks can further improve species recovery, even within novel environments. Future translocation planning should a priori identify potential refuges and sources to improve short-term recovery and long-term persistence.

Energetic balance is central to the survival and persistence of free‐ranging animals. Quantifying expenditures and identifying factors that drive energetics informs our understanding of species' ecology and their responses to shifting environmental conditions. Approaches used to estimate energetic expenditures of free‐ranging species, such as doubly‐labelled water (DLW), are precise but difficult to implement. Global positioning system (GPS) collars and accelerometers have emerged as alternatives for estimating expenditures, but these techniques have few applications in terrestrial species and no applications in small‐bodied (

The late Quaternary megafauna extinctions reshaped species assemblages, yet we know little about how extant obligate scavengers responded to this abrupt ecological change. To explore whether obligate scavengers persisted by depending on contemporary community linkages or via foraging flexibility, we tested the importance of the trophic interaction between pumas (Puma concolor) and native camelids (Vicugna vicugna and Lama guanicoe) for the persistence of Andean condors (Vultur gryphus) in southern South America, and compared the demographic history of three vultures in different continents. We sequenced and compiled mtDNA to reconstruct past population dynamics. Our results suggest that Andean condors increased in population size >10 KYA, whereas vicuñas and pumas showed stable populations and guanacos a recent (Gyps africanus) increased in population size, matching attenuated community changes in Africa, and California condors (Gymnogyps californianus) exhibited a steep demographic expansion ~20 KYA largely concurrent with North American megafaunal extinctions. Our results suggest that dietary plasticity of extant vulture lineages allowed them to thrive despite historical environmental changes. This dietary flexibility, however, is now detrimental as it enhances risk to toxicological compounds harbored by modern carrion resources.

Food subsidies from human sources are often exploited by free-ranging vertebrates living in human-dominated landscapes. To explore the importance and attempt to estimate the reliance of raccoons (Procyon lotor (Linnaeus, 1758)) — common synanthropes in North America — on such food subsidies, we analyzed hair samples from 122 raccoons collected across four states in the Midwestern United States (Wisconsin, Minnesota, Iowa, and Illinois), including 9 raccoons that were livetrapped and sampled in Madison (Wisconsin). We found that raccoons inhabiting areas with more agriculture had higher δ13C values, indicating a diet enriched with anthropogenic food from C4 photosynthetic plants, like corn (Zea mays L.). Surprisingly, raccoons inhabiting increasingly urban areas showed lower δ13C values, suggesting a diet with less anthropogenic food. Regardless, raccoons in urban areas enriched in 13C possessed high indices of body condition, suggesting that anthropogenic food subsidies are contributing to their overall nutritional condition. Our findings reveal that the degree to which synanthropes rely upon human foods differs by land-cover type and that the use of these calorically rich subsidies has important implications on individual health.

The study of mammals has promoted the development and testing of many ideas in contemporary ecology. Here we address recent developments in foraging and habitat selection, source–sink dynamics, competition (both within and between species), population cycles, predation (including apparent competition), mutualism, and biological invasions. Because mammals are appealing to the public, ecological insight gleaned from the study of mammals has disproportionate potential in educating the public about ecological principles and their application to wise management. Mammals have been central to many computational and statistical developments in recent years, including refinements to traditional approaches and metrics (e.g., capture-recapture) as well as advancements of novel and developing fields (e.g., spatial capture-recapture, occupancy modeling, integrated population models). The study of mammals also poses challenges in terms of fully characterizing dynamics in natural conditions. Ongoing climate change threatens to affect global ecosystems, and mammals provide visible and charismatic subjects for research on local and regional effects of such change as well as predictive modeling of the long-term effects on ecosystem function and stability. Although much remains to be done, the population ecology of mammals continues to be a vibrant and rapidly developing field. We anticipate that the next quarter century will prove as exciting and productive for the study of mammals as has the recent one.

The landscape of fear is an important driver of prey space use. However, prey can navigate the landscape of fear by exploiting temporal refuges from predation risk. We hypothesized that diel patterns of predator and prey movement and space use would be inversely correlated due to temporal constraints on predator habitat domain. Specifically, we evaluated habitat selection and activity of the vicuña and its only predator, the puma, during three diel periods: day, dawn/dusk, and night. Pumas selected the same habitats regardless of diel period-vegetated and rugged areas that feature stalking cover for pumas-but increased their activity levels during dawn/dusk and night when they benefit from reduced detection by prey. Vicuñas avoided areas selected by pumas and reduced activity at night, but selected vegetated areas and increased activity by day and dawn/dusk. Vicuña habitat selection and movement strategies appeared to reduce the risk of encountering pumas; movement rates of pumas and vicuñas were negatively correlated across the diel cycle, and habitat selection was negatively correlated during dawn/dusk and night. Our study shows that an ambush predator's temporal activity and space use patterns interact to create diel refugia and shape the antipredator behaviors of its prey. Importantly, it is likely the very nature of ambush predators' static habitat specificity that makes predator activity important to temporally varying perceptions of risk. Prey which depend on risky habitats for foraging appear to mitigate risk by feeding when they can more easily detect predators and when predators are least active.