Season, prey availability, sex, and age explain prey size selection in a large solitary carnivore

Prey selection is a fundamental aspect of ecology that drives evolution and community structure, yet the impact of intraspecific variation on the selection for prey size remains largely unaccounted for in ecological theory. Here, we explored puma (Puma concolor) prey selection across six study sites in North and South America. Our results highlighted the strong influence of season and prey availability on puma prey selection, and the smaller influence of puma age. Pumas in all sites selected smaller prey in warmer seasons following the ungulate birth pulse. Our top models included interaction terms between sex and age, suggesting that males more than females select larger prey as they age, which may reflect experiential learning. When accounting for variable sampling across pumas in our six sites, male and female pumas killed prey of equivalent size, even though males are larger than females, challenging assumptions about this species. Nevertheless, pumas in different study sites selected prey of different sizes, emphasizing that the optimal prey size for pumas is likely context-dependent and affected by prey availability. The mean prey weight across all sites averaged 1.18 times mean puma weight, which was less than predicted as the optimal prey size by energetics and ecological theory (optimal prey = 1.45 puma weight). Our results help refine our understanding of optimal prey for pumas and other solitary carnivores, as well as corroborate recent research emphasizing that carnivore prey selection is impacted not just by energetics but by the effects of diverse ecology.

The role of governance in rewilding the United States to stem the biodiversity crisis

A critical but underattended feature of the biodiversity crisis is the contraction of geographic range experienced by most studied terrestrial vertebrates. In the United States, the primary policy tool for mitigating the biodiversity crisis is a federal law, the Endangered Species Act (ESA). For the past two decades, the federal agencies that administer the ESA have interpreted the act in a manner that precludes treating this geographic element of the crisis. Therefore, the burden of mitigating the biodiversity crisis largely falls on wildlife agencies within state government, which are obligated to operate on behalf of the interests of their constituents. We present survey research indicating that most constituents expect state agencies to prioritize species restoration over other activities, including hunting. This prioritization holds even among self-identified hunters, which is significant because state agencies often take the provisioning of hunting opportunity as their top priority. By prioritizing rewilding efforts that restore native species throughout portions of their historic range, state agencies could unify hunting and nonhunting constituents while simultaneously stemming the biodiversity crisis.

Tourism and human computers offer new tools to monitor Patagonia's top carnivore

Monitoring wildlife populations to determine changing abundance is the basis for conservation strategies and interventions. Monitoring, however, is expensive, and we lack baseline data for countless species and landscapes around the globe. One solution is to utilize methods that leverage observations collected by everyday people. Humans are not only excellent sensors for diverse data, but possess a remarkable ability to process data and differentiate patterns with minimal training. Here, we explored the potential for people, including guides who work in tourism in southern Patagonia, to determine whether paired photographs of puma (Puma concolor puma) faces were the same individual, akin to a computer-led Siamese network analysis. Overall, participants performed well (average score of 92.2 %) and we detected no differences in local people versus those from the USA, or differences due to differential experience working with pumas. Based on these results, we built a historic capture-recapture dataset of individual pumas collected by local guides and report annual abundance for a portion of the Torres del Paine UNESCO Biosphere in southern Chile, an area lacking such data and of critical conservation for the species. Our results highlight the innate capabilities of human computers and their potential for contributing to wildlife surveys in novel ways to increase science capacity.

SNAPSHOT USA 2020: A second coordinated national camera trap survey of the United States during the COVID-19 pandemic

Managing wildlife populations in the face of global change requires regular data on the abundance and distribution of wild animals, but acquiring these over appropriate spatial scales in a sustainable way has proven challenging. Here we present the data from Snapshot USA 2020, a second annual national mammal survey of the USA. This project involved 152 scientists setting camera traps in a standardized protocol at 1485 locations across 103 arrays in 43 states for a total of 52,710 trap-nights of survey effort. Most (58) of these arrays were also sampled during the same months (September and October) in 2019, providing a direct comparison of animal populations in 2 years that includes data from both during and before the COVID-19 pandemic. All data were managed by the eMammal system, with all species identifications checked by at least two reviewers. In total, we recorded 117,415 detections of 78 species of wild mammals, 9236 detections of at least 43 species of birds, 15,851 detections of six domestic animals and 23,825 detections of humans or their vehicles. Spatial differences across arrays explained more variation in the relative abundance than temporal variation across years for all 38 species modeled, although there are examples of significant site-level differences among years for many species. Temporal results show how species allocate their time and can be used to study species interactions, including between humans and wildlife. These data provide a snapshot of the mammal community of the USA for 2020 and will be useful for exploring the drivers of spatial and temporal changes in relative abundance and distribution, and the impacts of species interactions on daily activity patterns. There are no copyright restrictions, and please cite this paper when using these data, or a subset of these data, for publication.

Standardizing protocols for determining the cause of mortality in wildlife studies

Mortality site investigations of telemetered wildlife are important for cause‐specific survival analyses and understanding underlying causes of observed population dynamics. Yet, eroding ecoliteracy and a lack of quality control in data collection can lead researchers to make incorrect conclusions, which may negatively impact management decisions for wildlife populations. We reviewed a random sample of 50 peer‐reviewed studies published between 2000 and 2019 on survival and cause‐specific mortality of ungulates monitored with telemetry devices. This concise review revealed extensive variation in reporting of field procedures, with many studies omitting critical information for the cause of mortality inference. Field protocols used to investigate mortality sites and ascertain the cause of mortality are often minimally described and frequently fail to address how investigators dealt with uncertainty. We outline a step‐by‐step procedure for mortality site investigations of telemetered ungulates, including evidence that should be documented in the field. Specifically, we highlight data that can be useful to differentiate predation from scavenging and more conclusively identify the predator species that killed the ungulate. We also outline how uncertainty in identifying the cause of mortality could be acknowledged and reported. We demonstrate the importance of rigorous protocols and prompt site investigations using data from our 5‐year study on survival and cause‐specific mortality of telemetered mule deer (Odocoileus hemionus) in northern California. Over the course of our study, we visited mortality sites of neonates (n = 91) and adults (n = 23) to ascertain the cause of mortality. Rapid site visitations significantly improved the successful identification of the cause of mortality and confidence levels for neonates. We discuss the need for rigorous and standardized protocols that include measures of confidence for mortality site investigations. We invite reviewers and journal editors to encourage authors to provide supportive information associated with the identification of causes of mortality, including uncertainty.

Kill rates and associated ecological factors for an apex predator

Kill rates and functional responses are fundamental to the study of predator ecology and the understanding of predatory-prey dynamics. As the most widely distributed apex predator in the western hemisphere, pumas (Puma concolor) have been well studied, yet a synthesis of their kill rates is currently lacking. We reviewed the literature and compiled data on sex- and age-specific kill rate estimates of pumas on ungulates, and conducted analyses aimed at understanding ecological factors explaining the observed spatial variation. Kill rate studies on pumas, while numerous, were primarily conducted in Temperate Conifer Forests (< 10% of puma range), revealing a dearth of knowledge across much of their range, especially from tropical and subtropical habitats. Across studies, kill rates in ungulates/week were highest for adult females with kitten(s) (1.24 ± 0.41 ungulates/week) but did not vary significantly between adult males (0.84 ± 0.18) and solitary adult females (0.99 ± 0.26). Kill rates in kg/day differed only marginally among reproductive classes. Kill rates of adult pumas increased with ungulate density, particularly for males. Ungulate species richness had a weak negative association with adult male kill rates. Neither scavenger richness, puma density, the proportion of non-ungulate prey in the diet, nor regional human population density had a significant effect on ungulate kill rates, but additional studies and standardization would provide further insights. Our results had a strong temperate-ecosystem bias highlighting the need for further research across the diverse biomes pumas occupy to fully interpret kill rates for the species. Data from more populations would also allow for multivariate analyses providing deeper inference into the ecological and behavioural factors driving kill rates and functional responses of pumas, and apex predators in general.

Functional traits driving species role in the structure of terrestrial vertebrate scavenger networks

Species assemblages often have a non-random nested organization, which in vertebrate scavenger (carrion-consuming) assemblages is thought to be driven by facilitation in competitive environments. However, not all scavenger species play the same role in maintaining assemblage structure, as some species are obligate scavengers (i.e., vultures) and others are facultative, scavenging opportunistically. We used a database with 177 vertebrate scavenger species from 53 assemblages in 22 countries across five continents to identify which functional traits of scavenger species are key to maintaining the scavenging network structure. We used network analyses to relate ten traits hypothesized to affect assemblage structure with the "role" of each species in the scavenging assemblage in which it appeared. We characterized the role of a species in terms of both the proportion of monitored carcasses on which that species scavenged, or scavenging breadth (i.e., the species "normalized degree"), and the role of that species in the nested structure of the assemblage (i.e., the species "paired nested degree"), therefore identifying possible facilitative interactions among species. We found that species with high olfactory acuity, social foragers, and obligate scavengers had the widest scavenging breadth. We also found that social foragers had a large paired nested degree in scavenger assemblages, probably because their presence is easier to detect by other species to signal carcass occurrence. Our study highlights differences in the functional roles of scavenger species and can be used to identify key species for targeted conservation to maintain the ecological function of scavenger assemblages.

Disturbance type and species life history predict mammal responses to humans

Human activity and land use change impact every landscape on Earth, driving declines in many animal species while benefiting others. Species ecological and life history traits may predict success in human-dominated landscapes such that only species with "winning" combinations of traits will persist in disturbed environments. However, this link between species traits and successful coexistence with humans remains obscured by the complexity of anthropogenic disturbances and variability among study systems. We compiled detection data for 24 mammal species from 61 populations across North America to quantify the effects of (1) the direct presence of people and (2) the human footprint (landscape modification) on mammal occurrence and activity levels. Thirty-three percent of mammal species exhibited a net negative response (i.e., reduced occurrence or activity) to increasing human presence and/or footprint across populations, whereas 58% of species were positively associated with increasing disturbance. However, apparent benefits of human presence and footprint tended to decrease or disappear at higher disturbance levels, indicative of thresholds in mammal species' capacity to tolerate disturbance or exploit human-dominated landscapes. Species ecological and life history traits were strong predictors of their responses to human footprint, with increasing footprint favoring smaller, less carnivorous, faster-reproducing species. The positive and negative effects of human presence were distributed more randomly with respect to species trait values, with apparent winners and losers across a range of body sizes and dietary guilds. Differential responses by some species to human presence and human footprint highlight the importance of considering these two forms of human disturbance separately when estimating anthropogenic impacts on wildlife. Our approach provides insights into the complex mechanisms through which human activities shape mammal communities globally, revealing the drivers of the loss of larger predators in human-modified landscapes.

Online Noise as Illustrated by Pitfalls and Biogeography Associated With Common Names for Puma concolor

Noise is the non-target search results that people encounter when searching for a particular topic of interest; it is also the cloud of distracting data that can obscure or deflect conservation communication. Online noise associated with large carnivores is particularly dense because their defining characteristics make them salient. Mountain lions (Puma concolor) exemplify noise associated with multiple vernaculars for a species in the crosshairs of conservation conundrums. We compared internet search results, Google Trends reflecting topic interest, use in science publications and sentiment in print and online media for P. concolor's most frequent vernacular names, “mountain lion,” “cougar,” “puma” and “Florida panther.” Puma and panther exhibited greater noise and salience than cougar or mountain lion, but, results for mountain lion, followed by cougar, yielded the highest biological relevance. Online sentiment negatively correlated with biological relevance, with positive sentiment highest for the noisiest vernaculars, puma and panther. As conservation practitioners, we must recognize that public outreach is part of our scientific agenda and be conscious of crafting communication that reaches and resonates with our intended audiences.

Reintroduced wolves and hunting limit the abundance of a subordinate apex predator in a multi-use landscape

Top-down effects of apex predators are modulated by human impacts on community composition and species abundances. Consequently, research supporting top-down effects of apex predators occurs almost entirely within protected areas rather than the multi-use landscapes dominating modern ecosystems. Here, we developed an integrated population model to disentangle the concurrent contributions of a reintroduced apex predator, the grey wolf, human hunting and prey abundances on vital rates and abundance of a subordinate apex predator, the puma. Increasing wolf numbers had strong negative effects on puma fecundity, and subadult and adult survival. Puma survival was also influenced by density dependence. Overall, puma dynamics in our multi-use landscape were more strongly influenced by top-down forces exhibited by a reintroduced apex predator, than by human hunting or bottom-up forces (prey abundance) subsidized by humans. Quantitatively, the average annual impact of human hunting on equilibrium puma abundance was equivalent to the effects of 20 wolves. Historically, wolves may have limited pumas across North America and dictated puma scarcity in systems lacking sufficient refugia to mitigate the effects of competition.

Motion-triggered video cameras reveal spatial and temporal patterns of red fox foraging on carrion provided by mountain lions

Carrion is a rich, ephemeral resource vital to biodiversity and ecosystem health. In temperate ecosystems in which cold temperatures and snowfall influence the accessibility and availability of small prey and seasonal mast crops, carrion may also be a limiting resource for mesocarnivores like red foxes (Vulpes vulpes), which are too small to predate ungulates. Using motion-triggered video cameras and generalized linear mixed models, we studied the spatial and temporal patterns of red fox scavenging at 232 mountain lion kills in the southern Greater Yellowstone Ecosystem (GYE) from 2012-2015. We found that red foxes scavenged mountain lion kills across all habitats throughout the year, however, red fox behaviors varied with season. In winter, we documented red foxes at a greater proportion of mountain lion kills (70.3% in winter vs. 48.9% in summer), and in greater numbers (1.83 foxes per kill in winter vs. 1.16 in summer). In winter, red foxes fed longer (= 102.7 ± 138.3 minutes feeding in winter vs. = 39.7 ± 74.0 in summer), and they more often scavenged while the mountain lion was nearby. We speculated that red foxes may have increased risk taking in winter due to hunger driven by resource scarcity. Our research highlighted an important ecological relationship between red foxes and mountain lions in the GYE. Mountain lions tolerate high levels of scavenging, so the frequency and intensity of red fox scavenging at their kills may not impact mountain lions, but instead facilitate the dispersion and benefits of resources created by this apex predator. Large carnivores, and mid-trophic felids like mountain lions in particular, are essential producers of carrion vital to biodiversity and ecosystem health. In turn, scavengers play critical roles in distributing these resources and increasing the heterogeneity of resources that support biodiversity and ecosystem structure, as well as ecological resilience.

Multiple anthropogenic interventions drive puma survival following wolf recovery in the Greater Yellowstone Ecosystem

Humans are primary drivers of declining abundances and extirpation of large carnivores worldwide. Management interventions to restore biodiversity patterns, however, include carnivore reintroductions, despite the many unresolved ecological consequences associated with such efforts. Using multistate capture-mark-recapture models, we explored age-specific survival and cause-specific mortality rates for 134 pumas (Puma concolor) monitored in the Greater Yellowstone Ecosystem during gray wolf (Canis lupus) recovery. We identified two top models explaining differences in puma survivorship, and our results suggested three management interventions (unsustainable puma hunting, reduction in a primary prey, and reintroduction of a dominant competitor) have unintentionally impacted puma survival. Specifically, puma survival across age classes was lower in the 6-month hunting season than the 6-month nonhunting season; human-caused mortality rates for juveniles and adults, and predation rates on puma kittens, were higher in the hunting season. Predation on puma kittens, and starvation rates for all pumas, also increased as managers reduced elk (Cervus elaphus) abundance in the system, highlighting direct and indirect effects of competition between recovering wolves and pumas over prey. Our results emphasize the importance of understanding the synergistic effects of existing management strategies and the recovery of large, dominant carnivores to effectively conserve subordinate, hunted carnivores in human-dominated landscapes.

Are pumas subordinate carnivores, and does it matter?

BACKGROUND

Interspecific competition affects species fitness, community assemblages and structure, and the geographic distributions of species. Established dominance hierarchies among species mitigate the need for fighting and contribute to the realized niche for subordinate species. This is especially important for apex predators, many of which simultaneous contend with the costs of competition with more dominant species and the costs associated with human hunting and lethal management.

METHODS

Pumas are a widespread solitary felid heavily regulated through hunting to reduce conflicts with livestock and people. Across their range, pumas overlap with six apex predators (gray wolf, grizzly bear, American black bear, jaguar, coyote, maned wolf), two of which (gray wolf, grizzly bear) are currently expanding in North America following recovery efforts. We conducted a literature search to assess whether pumas were subordinate or dominant with sympatric apex predators, as well as with three felid mesocarnivores with similar ecology (ocelot, bobcat, Canada lynx). We also conducted an analysis of the spatial distributions of pumas and their dominant sympatric competitors to estimate in what part of their range, pumas are dominant versus subordinate.

RESULTS

We used 64 sources to assess dominance among pumas and other apex predators, and 13 sources to assess their relationships with felid mesocarnivores. Evidence suggested that wolves, grizzly bears, black bears, and jaguars are dominant over pumas, but that pumas are dominant over coyotes and maned wolves. Evidence suggested that pumas are also dominant over all three felid mesocarnivores with which they share range. More broadly, pumas are subordinate to at least one other apex carnivore in 10,799,252 (47.5%) of their 22,735,268 km2 range across North and South America.

DISCUSSION

Subordinate pumas change their habitat use, suffer displacement at food sources, likely experience increased energetic demands from harassment, exhibit increased starvation, and are sometimes directly killed in competitive interactions with dominant competitors. Nevertheless, we lack research clearly linking the costs of competition to puma fitness. Further, we lack research that assesses the influence of human effects simultaneous with the negative effects of competition with other sympatric carnivores. Until the time that we understand whether competitive effects are additive with human management, or even potentially synergistic, we encourage caution among managers responsible for determining harvest limits for pumas and other subordinate, apex carnivores in areas where they are sympatric with dominant species. This may be especially important information for managers working in regions where wolves and brown bears are recolonizing and recovering, and historic competition scenarios among multiple apex predators are being realized.

Bed site selection by a subordinate predator: an example with the cougar (Puma concolor) in the Greater Yellowstone Ecosystem

As technology has improved, our ability to study cryptic animal behavior has increased. Bed site selection is one such example. Among prey species, bed site selection provides thermoregulatory benefits and mitigates predation risk, and may directly influence survival. We conducted research to test whether a subordinate carnivore also selected beds with similar characteristics in an ecosystem supporting a multi-species guild of competing predators. We employed a model comparison approach in which we tested whether cougar (Puma concolor) bed site attributes supported the thermoregulatory versus the predator avoidance hypotheses, or exhibited characteristics supporting both hypotheses. Between 2012-2016, we investigated 599 cougar bed sites in the Greater Yellowstone Ecosystem and examined attributes at two scales: the landscape (second-order, n = 599) and the microsite (fourth order, n = 140). At the landscape scale, cougars selected bed sites in winter that supported both the thermoregulatory and predator avoidance hypotheses: bed sites were on steeper slopes but at lower elevations, closer to the forest edge, away from sagebrush and meadow habitat types, and on southern, eastern, and western-facing slopes. In the summer, bed attributes supported the predator avoidance hypothesis over the thermoregulation hypothesis: beds were closer to forest edges, away from sagebrush and meadow habitat classes, and on steeper slopes. At the microsite scale, cougar bed attributes in both the winter and summer supported both the predator avoidance and thermoregulatory hypotheses: they selected bed sites with high canopy cover, high vegetative concealment, and in a rugged habitat class characterized by cliff bands and talus fields. We found that just like prey species, a subordinate predator selected bed sites that facilitated both thermoregulatory and anti-predator functions. In conclusion, we believe that measuring bed site attributes may provide a novel means of measuring the use of refugia by subordinate predators, and ultimately provide new insights into the habitat requirements and energetics of subordinate carnivores.

Adaptive social strategies in a solitary carnivore

Cost-benefit trade-offs for individuals participating in social behaviors are the basis for current theories on the evolution of social behaviors and societies. However, research on social strategies has largely ignored solitary animals, in which we assume that rare interactions are explained by courtship or territoriality or, in special circumstances, resource distributions or kinship. We used directed network analysis of conspecific tolerance at food sources to provide evidence that a solitary carnivore, the puma (Puma concolor), exhibited adaptive social strategies similar to more social animals. Every puma in our analysis participated in the network, which featured densely connected communities delineated by territorial males. Territorial males also structured social interactions among pumas. Contrary to expectations, conspecific tolerance was best characterized by direct reciprocity, establishing a fitness benefit to individuals that participated in social behaviors. However, reciprocity operated on a longer time scale than in gregarious species. Tolerance was also explained by hierarchical reciprocity, which we defined as network triangles in which one puma (generally male) received tolerance from two others (generally females) that also tolerated each other. Hierarchical reciprocity suggested that males might be cheating females; nevertheless, we suspect that males and females used different fitness currencies. For example, females may have benefited from tolerating males through the maintenance of social niches that support breeding opportunities. Our work contributes evidence of adaptive social strategies in a solitary carnivore and support for the applicability of theories of social behavior across taxa, including solitary species in which they are rarely tested.

Social interactions in a solitary carnivore

In total, 177 of 245 terrestrial carnivores are described as solitary, and much of carnivore ecology is built on the assumptions that interactions between adult solitary carnivores are rare. We employed Global Positioning System (GPS) technology and motion-triggered cameras to test predictions of land-tenure territoriality and the resource dispersion hypothesis in a territorial carnivore, the puma Puma concolor. We documented 89 independent GPS interactions, 60% of which occurred at puma kills (n = 53), 59 camera interactions, 11 (17%) of which captured courtship behaviors, and 5 other interactions (1 F-F, 3 M-F, and 1 M-M). Mean minimum weekly contact rates were 5.5 times higher in winter, the season when elk Cervus elaphus were aggregated at lower elevations and during which puma courtship primarily occurred. In winter, contacts rates were 0.6 ± 0.3 (standard deviation (SD)) interactions/week vs. 0.1 ± 0.1 (SD) interactions/week during summer. The preponderance of interactions at food sources supported the resource dispersion hypothesis, which predicts that resource fluxes can explain temporary social behaviors that do not result in any apparent benefits for the individuals involved. Conspecific tolerance is logical when a prey is so large that the predator that killed it cannot consume it entirely, and thus, the costs of tolerating a conspecific sharing the kill are less than the potential costs associated with defending it and being injured. Puma aggregations at kills numbered as high as 9, emphasizing the need for future research on what explains tolerance among solitary carnivores.

Human–carnivore competition for antlered ungulates: do pumas select for bulls and bucks?

Context Many institutions of wildlife management and their hunting constituents tend to value ungulates over large carnivores, in part due to financial incentives associated with ungulate hunting over carnivore hunting. This system benefits from mythology that presents large carnivores as competitors for antlered male ungulates most prized by the hunting community. Aims We explored puma (Puma concolor) foraging and prey selection in two study areas in the Rocky Mountains, USA, to test whether pumas were competing with human hunters for antlered elk (Cervus elaphus) and mule deer (Odocoileus hemionus). Methods We employed GPS technology to track pumas and document their prey. We measured population- and individual-level selection by comparing prey killed by pumas to two estimates of prey availability: (1) landscape-level as determined by annual agency game counts; and (2) total prey killed by marked pumas. Key results Pumas in both study systems killed small numbers of antlered elk and mule deer. Pumas exhibited avoidance of mature elk, instead strongly selecting for elk calves over any other age or sex class. Pumas in both systems also selected for mule deer fawns; however, they also exhibited small positive selection (Jacob’s index of 0.08 in CO and 0.11 in WY on a scale of 0.0–1.0) for antlered mule deer. Conclusions In terms of numbers killed, pumas were not a competitor with human hunters for either antlered species. In terms of prey selection, pumas showed that they may be greater competition for rare antlered mule deer but not for antlered elk. In both study sites, antlered elk and deer remained at levels at which they could perform their ecological functions. Implications Our results highlight the fact that the overhunting of large carnivores over competition for antlered ungulates is mostly unfounded; we should instead focus management, media attention and conservation science on disentangling the complex ecology driving localised declines of mule deer, elk and other important ungulate resources, many of which are anthropogenic in nature and can be addressed.

The importance of motivation, weapons, and foul odors in driving encounter competition in carnivores

Encounter competition is interference competition in which animals directly contend for resources. Ecological theory predicts the trait that determines the resource holding potential (RHP), and hence the winner of encounter competition, is most often body size or mass. The difficulties of observing encounter competition in complex organisms in natural environments, however, has limited opportunities to test this theory across diverse species. We studied the outcome of encounter competition contests among mesocarnivores at deer carcasses in California to determine the most important variables for winning these contests. We found some support for current theory in that body mass is important in determining the winner of encounter competition, but we found that other factors including hunger and species-specific traits were also important. In particular, our top models were "strength and hunger" and "size and hunger," with models emphasizing the complexity of variables influencing outcomes of encounter competition. In addition, our wins above predicted (WAP) statistic suggests that an important aspect that determines the winner of encounter competition is species-specific advantages that increase their RHP, as bobcats (Lynx rufus) and spotted skunks (Spilogale gracilis) won more often than predicted based on mass. In complex organisms, such as mesocarnivores, species-specific adaptations, including strategic behaviors, aggressiveness, and weapons, contribute to competitive advantages and may allow certain species to take control or defend resources better than others. Our results help explain how interspecific competition shapes the occurrence patterns of species in ecological communities.

Population- and individual-level prey selection by a solitary predator as determined with two estimates of prey availability

Prey selection is exhibited by predator populations that kill a prey species disproportionate to its availability, or alternatively, individual predators that select prey disproportionate to the mean selection exhibited by their populations. Prey selection is a simple calculation when one can determine prey availability; however, measuring prey availability is challenging. We compared population- and individual-level prey selection as determined with two measures of prey availability for five ungulate species killed by pumas (Puma concolor (L., 1771)) in the Southern Yellowstone Ecosystem, USA: (1) annual prey counts and (2) total prey killed by marked pumas. We also tested whether individual pumas in the population exhibited a narrower dietary niche breadth compared with their population as a whole. The two methods yielded different estimates of prey availability and highlighted the need to consciously match prey availability estimates with appropriate ecological questions. Prey counts may have overestimated elk (Cervus canadensis (Erxleben, 1777)) abundance and underestimated deer abundance, whereas predation data may have better captured the influence of prey size on puma-specific prey vulnerability and availability. Prey counts were the more appropriate metric for analyzing population-level prey selection or differences in interspecific foraging, whereas total prey killed was the more appropriate metric for intraspecific comparisons.

The comparative effects of large carnivores on the acquisition of carrion by scavengers

Pumas (Puma concolor) and black bears (Ursus americanus) are large carnivores that may influence scavenger population dynamics. We used motion-triggered video cameras deployed at deer carcasses to determine how pumas and black bears affected three aspects of carrion acquisition by scavengers: presence, total feeding time, and mean feeding-bout duration. We found that pumas were unable to limit acquisition of carrion by large carnivores but did limit aspects of carrion acquisition by both birds and mesocarnivores. Through their suppression of mesocarnivores and birds, pumas apparently initiated a cascading pattern and increased carrion acquisition by small carnivores. In contrast, black bears monopolized carrion resources and generally had larger limiting effects on carrion acquisition by all scavengers. Black bears also limited puma feeding behaviors at puma kills, which may require pumas to compensate for energetic losses through increasing their kill rates of ungulates. Our results suggest that pumas provide carrion and selectively influence species acquiring carrion, while black bears limit carrion availability to all other scavengers. These results suggest that the effects of large carnivores on scavengers depend on attributes of both carnivores and scavengers (including size) and that competition for carcasses may result in intraguild predation as well as mesocarnivore release.

Trophic facilitation or limitation? Comparative effects of pumas and black bears on the scavenger community

Scavenging is a widespread behaviour and an important process influencing food webs and ecological communities. Large carnivores facilitate the movement of energy across trophic levels through the scavenging and decomposition of their killed prey, but competition with large carnivores is also likely to constrain acquisition of carrion by scavengers. We used an experimental approach based on motion-triggered video cameras at black-tailed deer (Odocoileus hemionus columbianus) carcasses to measure the comparative influences of two large carnivores in the facilitation and limitation of carrion acquisition by scavengers. We found that pumas (Puma concolor) and black bears (Ursus americanus) had different effects on their ecological communities. Pumas, as a top-level predator, facilitated the consumption of carrion by scavengers, despite significantly reducing their observed sum feeding times (165.7 min ± 21.2 SE at puma kills 264.3 min ± 30.1 SE at control carcasses). In contrast, black bears, as the dominant scavenger in the system, limited consumption of carrion by scavengers as evidenced by the observed reduction of scavenger species richness recorded at carcasses where they were present (mean = 2.33 ± 0.28 SE), compared to where they were absent (mean = 3.28 ± 0.23 SE). Black bears also had large negative effects on scavenger sum feeding times (88.5 min ± 19.8 SE at carcasses where bears were present, 372.3 min ± 50.0 SE at carcasses where bears were absent). In addition, we found that pumas and black bears both increased the nestedness (a higher level of order among species present) of the scavenger community. Our results suggest that scavengers have species-specific adaptions to exploit carrion despite large carnivores, and that large carnivores influence the structure and composition of scavenger communities. The interactions between large carnivores and scavengers should be considered in future studies of food webs and ecological communities.

Seasonal foraging ecology of non-migratory cougars in a system with migrating prey

We tested for seasonal differences in cougar (Puma concolor) foraging behaviors in the Southern Yellowstone Ecosystem, a multi-prey system in which ungulate prey migrate, and cougars do not. We recorded 411 winter prey and 239 summer prey killed by 28 female and 10 male cougars, and an additional 37 prey items by unmarked cougars. Deer composed 42.4% of summer cougar diets but only 7.2% of winter diets. Males and females, however, selected different proportions of different prey; male cougars selected more elk (Cervus elaphus) and moose (Alces alces) than females, while females killed greater proportions of bighorn sheep (Ovis canadensis), pronghorn (Antilocapra americana), mule deer (Odocoileus hemionus) and small prey than males. Kill rates did not vary by season or between males and females. In winter, cougars were more likely to kill prey on the landscape as: 1) elevation decreased, 2) distance to edge habitat decreased, 3) distance to large bodies of water decreased, and 4) steepness increased, whereas in summer, cougars were more likely to kill in areas as: 1) elevation decreased, 2) distance to edge habitat decreased, and 3) distance from large bodies of water increased. Our work highlighted that seasonal prey selection exhibited by stationary carnivores in systems with migratory prey is not only driven by changing prey vulnerability, but also by changing prey abundances. Elk and deer migrations may also be sustaining stationary cougar populations and creating apparent competition scenarios that result in higher predation rates on migratory bighorn sheep in winter and pronghorn in summer. Nevertheless, cougar predation on rare ungulates also appeared to be influenced by individual prey selection.

Conservation strategies for species affected by apparent competition

Apparent competition is an indirect interaction between 2 or more prey species through a shared predator, and it is increasingly recognized as a mechanism of the decline and extinction of many species. Through case studies, we evaluated the effectiveness of 4 management strategies for species affected by apparent competition: predator control, reduction in the abundances of alternate prey, simultaneous control of predators and alternate prey, and no active management of predators or alternate prey. Solely reducing predator abundances rapidly increased abundances of alternate and rare prey, but observed increases are likely short-lived due to fast increases in predator abundance following the cessation of control efforts. Substantial reductions of an abundant alternate prey resulted in increased predation on endangered huemul (Hippocamelus bisulcus) deer in Chilean Patagonia, which highlights potential risks associated with solely reducing alternate prey species. Simultaneous removal of predators and alternate prey increased survival of island foxes (Urocyon littoralis) in California (U.S.A.) above a threshold required for population recovery. In the absence of active management, populations of rare woodland caribou (Rangifer tarandus caribou) continued to decline in British Columbia, Canada. On the basis of the cases we examined, we suggest the simultaneous control of predators and alternate prey is the management strategy most likely to increase abundances and probabilities of persistence of rare prey over the long term. Knowing the mechanisms driving changes in species' abundances before implementing any management intervention is critical. We suggest scientists can best contribute to the conservation of species affected by apparent competition by clearly communicating the biological and demographic forces at play to policy makers responsible for the implementation of proposed management actions.

Nuisance ecology: do scavenging condors exact foraging costs on pumas in Patagonia?

Predation risk describes the energetic cost an animal suffers when making a trade off between maximizing energy intake and minimizing threats to its survival. We tested whether Andean condors (Vultur gryphus) influenced the foraging behaviors of a top predator in Patagonia, the puma (Puma concolor), in ways comparable to direct risks of predation for prey to address three questions: 1) Do condors exact a foraging cost on pumas?; 2) If so, do pumas exhibit behaviors indicative of these risks?; and 3) Do pumas display predictable behaviors associated with prey species foraging in risky environments? Using GPS location data, we located 433 kill sites of 9 pumas and quantified their kill rates. Based upon time pumas spent at a carcass, we quantified handling time. Pumas abandoned >10% of edible meat at 133 of 266 large carcasses after a single night, and did so most often in open grasslands where their carcasses were easily detected by condors. Our data suggested that condors exacted foraging costs on pumas by significantly decreasing puma handling times at carcasses, and that pumas increased their kill rates by 50% relative to those reported for North America to compensate for these losses. Finally, we determined that the relative risks of detection and associated harassment by condors, rather than prey densities, explained puma "giving up times" (GUTs) across structurally variable risk classes in the study area, and that, like many prey species, pumas disproportionately hunted in high-risk, high-resource reward areas.

Table scraps: inter-trophic food provisioning by pumas

Large carnivores perform keystone ecological functions through direct predation, or indirectly, through food subsidies to scavengers or trophic cascades driven by their influence on the distributions of their prey. Pumas (Puma concolor) are an elusive, cryptic species difficult to study and little is known about their inter-trophic-level interactions in natural communities. Using new GPS technology, we discovered that pumas in Patagonia provided 232 ± 31 kg of edible meat/month/100 km(2) to near-threatened Andean condors (Vultur gryphus) and other members of a diverse scavenger community. This is up to 3.1 times the contributions by wolves (Canis lupus) to communities in Yellowstone National Park, USA, and highlights the keystone role large, solitary felids play in natural systems. These findings are more pertinent than ever, for managers increasingly advocate controlling pumas and other large felids to bolster prey populations and mitigate concerns over human and livestock safety, without a full understanding of the potential ecological consequences of their actions.