White-tailed deer population dynamics in a multipredator landscape shaped by humans.

Large terrestrial mammals increasingly rely on human-modified landscapes as anthropogenic footprints expand. Land management activities such as timber harvest, agriculture, and roads can influence prey population dynamics by altering forage resources and predation risk via changes in habitat, but these effects are not well understood in regions with diverse and changing predator guilds. In northeastern Washington state, USA, white-tailed deer (Odocoileus virginianus) are vulnerable to multiple carnivores, including recently returned gray wolves (Canis lupus), within a highly human-modified landscape. To understand the factors governing predator-prey dynamics in a human context, we radio-collared 280 white-tailed deer, 33 bobcats (Lynx rufus), 50 cougars (Puma concolor), 28 coyotes (C. latrans), and 14 wolves between 2016 and 2021. We first estimated deer vital rates and used a stage-structured matrix model to estimate their population growth rate. During the study, we observed a stable to declining deer population (lambda = 0.97, 95% confidence interval: 0.88, 1.05), with 74% of Monte Carlo simulations indicating population decrease and 26% of simulations indicating population increase. We then fit Cox proportional hazard models to evaluate how predator exposure, use of human-modified landscapes, and winter severity influenced deer survival and used these relationships to evaluate impacts on overall population growth. We found that the population growth rate was dually influenced by a negative direct effect of apex predators and a positive effect of timber harvest and agricultural areas. Cougars had a stronger effect on deer population dynamics than wolves, and mesopredators had little influence on the deer population growth rate. Areas of recent timber harvest had 55% more forage biomass than older forests, but horizontal visibility did not differ, suggesting that timber harvest did not influence predation risk. Although proximity to roads did not affect the overall population growth rate, vehicle collisions caused a substantial proportion of deer mortalities, and reducing these collisions could be a win-win for deer and humans. The influence of apex predators and forage indicates a dual limitation by top-down and bottom-up factors in this highly human-modified system, suggesting that a reduction in apex predators would intensify density-dependent regulation of the deer population owing to limited forage availability.

Are we telling the same story? Comparing inferences made from camera trap and telemetry data for wildlife monitoring.

Estimating habitat and spatial associations for wildlife is common across ecological studies and it is well known that individual traits can drive population dynamics and vice versa. Thus, it is commonly assumed that individual- and population-level data should represent the same underlying processes, but few studies have directly compared contemporaneous data representing these different perspectives. We evaluated the circumstances under which data collected from Lagrangian (individual-level) and Eulerian (population-level) perspectives could yield comparable inference to understand how scalable information is from the individual to the population. We used Global Positioning System (GPS) collar (Lagrangian) and camera trap (Eulerian) data for seven species collected simultaneously in eastern Washington (2018-2020) to compare inferences made from different survey perspectives. We fit the respective data streams to resource selection functions (RSFs) and occupancy models and compared estimated habitat- and space-use patterns for each species. Although previous studies have considered whether individual- and population-level data generated comparable information, ours is the first to make this comparison for multiple species simultaneously and to specifically ask whether inferences from the two perspectives differed depending on the focal species. We found general agreement between the predicted spatial distributions for most paired analyses, although specific habitat relationships differed. We hypothesize the discrepancies arose due to differences in statistical power associated with camera and GPS-collar sampling, as well as spatial mismatches in the data. Our research suggests data collected from individual-based sampling methods can capture coarse population-wide patterns for a diversity of species, but results differ when interpreting specific wildlife-habitat relationships.

Interactive effects of wildfires, season and predator activity shape mule deer movements.

Wildfires are increasing in size, frequency and severity due to climate change and fire suppression, but the direct and indirect effects on wildlife remain largely unresolved. Fire removes forest canopy, which can improve forage for ungulates but also reduce snow interception, leading to a deeper snowpack and potentially increased vulnerability to predation in winter. If ungulates exhibit predator-mediated foraging, burns should generally be selected for in summer to access high-quality forage and avoided in winter to reduce predation risk in deep snow. Fires also typically increase the amount of deadfall and initiate the growth of dense understory vegetation, creating obstacles that may confer a hunting advantage to stalking predators and a disadvantage to coursing predators. To minimize risk, ungulates may therefore avoid burns when and where stalking predators are most active, and use burns when and where coursing predators are most active. We used telemetry data from GPS-collared mule deer (Odocoileus hemionus), cougars (Puma concolor) and wolves (Canis lupus) to develop step selection functions to examine how mule deer navigated species-specific predation risk across a landscape in northern Washington, USA, that has experienced substantial wildfire activity during the past several decades. We considered a diverse array of wildfire impacts, accounting for both the severity of the fire and time since the burn (1-35 years) in our analyses. We observed support for the predator mediating foraging hypothesis: mule deer generally selected for burned areas in summer and avoided burns in winter. In addition, deer increased use of burned areas when and where wolf activity was high and avoided burns when and where cougar use was high in winter, suggesting the hunting mode of resident predators mediated the seasonal response of deer to burns. Deer were not more likely to die by predation in burned than in unburned areas, indicating that they adequately manage fire-induced changes to predation risk. As fire activity increases with climate change, our findings indicate the impact on ungulates will depend on trade-offs between enhanced summer forage and functionally reduced winter range, mediated by characteristics of the predator community.

The context dependence of non-consumptive predator effects.

Non-consumptive predator effects (NCEs) are now widely recognised for their capacity to shape ecosystem structure and function. Yet, forecasting the propagation of these predator-induced trait changes through particular communities remains a challenge. Accordingly, focusing on plasticity in prey anti-predator behaviours, we conceptualise the multi-stage process by which predators trigger direct and indirect NCEs, review and distil potential drivers of contingencies into three key categories (properties of the prey, predator and setting), and then provide a general framework for predicting both the nature and strength of direct NCEs. Our review underscores the myriad factors that can generate NCE contingencies while guiding how research might better anticipate and account for them. Moreover, our synthesis highlights the value of mapping both habitat domains and prey-specific patterns of evasion success ('evasion landscapes') as the basis for predicting how direct NCEs are likely to manifest in any particular community. Looking ahead, we highlight two key knowledge gaps that continue to impede a comprehensive understanding of non-consumptive predator-prey interactions and their ecosystem consequences; namely, insufficient empirical exploration of (1) context-dependent indirect NCEs and (2) the ways in which direct and indirect NCEs are shaped interactively by multiple drivers of context dependence.

Loss of predation risk from apex predators can exacerbate marine tropicalization caused by extreme climatic events.

Extreme climatic events (ECEs) and predator removal represent some of the most widespread stressors to ecosystems. Though species interactions can alter ecological effects of climate change (and vice versa), it is less understood whether, when and how predator removal can interact with ECEs to exacerbate their effects. Understanding the circumstances under which such interactions might occur is critical because predator loss is widespread and ECEs can generate rapid phase shifts in ecosystems which can ultimately lead to tropicalization. Our goal was to determine whether loss of predation risk may be an important mechanism governing ecosystem responses to extreme events, and whether the effects of such events, such as tropicalization, can occur even when species range shifts do not. Specifically, our goal was to experimentally simulate the loss of an apex predator, the tiger shark Galeocerdo cuvier effects on a recently damaged seagrass ecosystem of Shark Bay, Australia by applying documented changes to risk-sensitive grazing of dugong Dugong dugon herbivores. Using a 16-month-field experiment established in recently disturbed seagrass meadows, we used previous estimates of risk-sensitive dugong foraging behaviour to simulate altered risk-sensitive foraging densities and strategies of dugongs consistent with apex predator loss, and tracked seagrass responses to the simulated grazing. Grazing treatments targeted and removed tropical seagrasses, which declined. However, like in other mixed-bed habitats where dugongs forage, treatments also incidentally accelerated temperate seagrass losses, revealing that herbivore behavioural changes in response to predator loss can exacerbate ECE and promote tropicalization, even without range expansions or introductions of novel species. Our results suggest that changes to herbivore behaviours triggered by loss of predation risk can undermine ecological resilience to ECEs, particularly where long-lived herbivores are abundant. By implication, ongoing losses of apex predators may combine with increasingly frequent ECEs to amplify climate change impacts across diverse ecosystems and large spatial scales.

Managing salmon for wildlife: Do fisheries limit salmon consumption by bears in small Alaskan streams?

Ecosystem-based management requires consideration of overlapping resource use between humans and other consumers. Pacific salmon are an important resource for both fisheries and populations of wildlife around the Pacific rim, including coastal brown bears (Ursus arctos); salmon consumption has been positively linked to bear density, body size, and reproductive rate. As a case study within the broader context of human-wildlife competition for food, we used 16-22 yr of empirical data in four different salmon-bearing systems in southwestern Alaska to explore the relationship between sockeye salmon (Oncorhynchus nerka) availability and consumption by bears. We found a negative relationship between the annual biomass of salmon available to bears and the fraction of biomass consumed per fish, and a saturating relationship between salmon availability and the total annual biomass of salmon consumed by bears. Under modeled scenarios, bear consumption of salmon was predicted to increase only with dramatic (on the order of 50-100%) increases in prey availability. Even such large increases in salmon abundance were estimated to produce relatively modest increases in per capita salmon consumption by bears (2.4-4.8 kg·bear-1 ·d-1 , 15-59% of the estimated daily maximum per capita intake), in part because bears did not consume salmon entirely, especially when salmon were most available. Thus, while bears catching salmon in small streams may be limited by salmon harvest in some years, current management of the systems we studied is sufficient for bear populations to reach maximum salmon consumption every 2-4 yr. Consequently, allocating more salmon for brown bear conservation would unlikely result in an ecologically significant response for bears in these systems, though other ecosystem components might benefit. Our results highlight the need for documenting empirical relationships between prey abundance and consumption, particularly in systems with partial consumption, when evaluating the ecological response of managing prey resources for wildlife populations.

Extinction risk is most acute for the world's largest and smallest vertebrates.

Extinction risk in vertebrates has been linked to large body size, but this putative relationship has only been explored for select taxa, with variable results. Using a newly assembled and taxonomically expansive database, we analyzed the relationships between extinction risk and body mass (27,647 species) and between extinction risk and range size (21,294 species) for vertebrates across six main classes. We found that the probability of being threatened was positively and significantly related to body mass for birds, cartilaginous fishes, and mammals. Bimodal relationships were evident for amphibians, reptiles, and bony fishes. Most importantly, a bimodal relationship was found across all vertebrates such that extinction risk changes around a body mass breakpoint of 0.035 kg, indicating that the lightest and heaviest vertebrates have elevated extinction risk. We also found range size to be an important predictor of the probability of being threatened, with strong negative relationships across nearly all taxa. A review of the drivers of extinction risk revealed that the heaviest vertebrates are most threatened by direct killing by humans. By contrast, the lightest vertebrates are most threatened by habitat loss and modification stemming especially from pollution, agricultural cropping, and logging. Our results offer insight into halting the ongoing wave of vertebrate extinctions by revealing the vulnerability of large and small taxa, and identifying size-specific threats. Moreover, they indicate that, without intervention, anthropogenic activities will soon precipitate a double truncation of the size distribution of the world's vertebrates, fundamentally reordering the structure of life on our planet.

Habitat use of sympatric prey suggests divergent anti-predator responses to recolonizing gray wolves.

The non-consumptive effects of predators on prey are now widely recognized, but the need remains for studies identifying the factors that determine how particular prey species respond behaviorally when threatened with predation. We took advantage of ongoing gray wolf (Canis lupus) recolonization in eastern Washington, USA, to contrast habitat use of two sympatric prey species-mule (Odocoileus hemionus) and white-tailed (O. virginianus) deer-at sites with and without established wolf packs. Under the hypothesis that the nature and scale of responses by these ungulates to wolf predation risk depend on their divergent flight tactics (i.e., modes of fleeing from an approaching predator), we predicted that (1) mule deer would respond to wolves with coarse-scale spatial shifts to rugged terrain favoring their stotting tactic; (2) white-tailed deer would manage wolf risk with fine-scale shifts toward gentle terrain facilitating their galloping tactic within their current home range. Resource selection functions based on 61 mule deer and 59 white-tailed deer equipped with GPS radio-collars from 2013 to 2016 revealed that habitat use for each species was altered by wolf presence, but in divergent ways that supported our predictions. Our findings add to a growing literature highlighting flight behavior as a viable predictor of prey responses to predation risk across multiple ecosystem types. Consequently, they suggest that predators could initiate multiple indirect non-consumptive effects in the same ecosystem that are transmitted by divergent responses of sympatric prey with different flight tactics.

Diverse foraging opportunities drive the functional response of local and landscape-scale bear predation on Pacific salmon.

The relationship between prey abundance and predation is often examined in single habitat units or populations, but predators may occupy landscapes with diverse habitats and foraging opportunities. The vulnerability of prey within populations may depend on habitat features that hinder predation, and increased density of conspecifics in both the immediate vicinity and the broader landscape. We evaluated the relative effects of physical habitat, local, and neighborhood prey density on predation by brown bears on sockeye salmon in a suite of 27 streams using hierarchical Bayesian functional response models. Stream depth and width were inversely related to the maximum proportion of salmon killed, but not the asymptotic limit on total number killed. Interannual variation in predation was density dependent; the number of salmon killed increased with fish density in each stream towards an asymptote. Seven streams in two geographical groups with ≥23 years of data in common were then analyzed for neighborhood density effects. In most (12 of 18) cases predation in a stream was reduced by increasing salmon abundance in neighboring streams. The uncertainty in the estimates for these neighborhood effects may have resulted from interactions between salmon abundance and habitat that influenced foraging by bears, and from bear behavior (e.g., competitive exclusion) and abundance. Taken together, the results indicated that predator-prey interactions depend on density at multiple spatial scales, and on habitat features of the surrounding landscape. Explicit consideration of this context dependency should lead to improved understanding of the ecological impacts of predation across ecosystems and taxa.

Accounting for individual behavioural variation in studies of habitat selection.

A caribou wearing an animal-borne video camera (a) and animal-borne video footage taken from systems deployed on mule deer (Odocoileus hemionus) in north-central Washington state, USA (b-d). When paired with tracking technology, animal-borne video can reveal detailed information about behaviour and environmental features at each location: (b) feeding, (c) vigilant in the open, (d) vigilant in cover, (e) resting in the open. Accordingly, animal-borne video systems should allow for analyses of habitat selection by individuals in particular behavioural states. In Focus: DeCesare, N.J., Hebblewhite, M., Bradley, M., Hervieux, D., Neufeld, L. & Musiani, M. (2014) Linking habitat selection and predation risk to spatial variation in survival. Journal of Animal Ecology, 83, 343-352. Resource selection is often assumed to confer enhanced fitness, but this assumption is rarely examined. In a study involving woodland caribou subject to grey wolf predation, DeCesare et al. (2014) show that while patterns of selection by caribou did correspond with a fitness proxy (survival probability), individuals did not avoid wolf predation risk to the extent that would minimize mortality. Here, we use the results of this paper as a springboard for discussing the choice of fitness proxies and the need to account for individual behavioural variation in studies of resource selection.

Cougars, wolves, and humans drive a dynamic landscape of fear for elk.

To manage predation risk, prey navigate a dynamic landscape of fear, or spatiotemporal variation in risk perception, reflecting predator distributions, traits, and activity cycles. Prey may seek to reduce risk across this landscape using habitat at times and in places when predators are less active. In multipredator landscapes, avoiding one predator could increase vulnerability to another, making the landscape of fear difficult to predict and navigate. Additionally, humans may shape interactions between predators and prey, and induce new sources of risk. Humans can function as a shield, providing a refuge for prey from human-averse carnivores, and as a predator, causing mortality through hunting and vehicle collisions and eliciting a fear response that can exceed that of carnivores. We used telemetry data collected between 2017 and 2021 from 63 Global Positioning System-collared elk (Cervus canadensis), 42 cougars (Puma concolor), and 16 wolves (Canis lupus) to examine how elk habitat selection changed in relation to carnivores and humans in northeastern Washington, USA. Using step selection functions, we evaluated elk habitat use in relation to cougars, wolves, and humans, diel period (daytime vs. nighttime), season (summer calving season vs. fall hunting season), and habitat structure (open vs. closed habitat). The diel cycle was critical to understanding elk movement, allowing elk to reduce encounters with predators where and when they would be the largest threat. Elk strongly avoided cougars at night but had a near-neutral response to cougars during the day, whereas elk avoided wolves at all times of day. Elk generally used more open habitats where cougars and wolves were most active, rather than altering the use of habitat structure depending on the predator species. Elk avoided humans during the day and ~80% of adult female mortality was human caused, suggesting that humans functioned as a "super predator" in this system. Simultaneously, elk leveraged the human shield against wolves but not cougars at night, and no elk were confirmed to have been killed by wolves. Our results add to the mounting evidence that humans profoundly affect predator-prey interactions, highlighting the importance of studying these dynamics in anthropogenic areas.

Scavenging with invasive species.

Carrion acts as a hotspot of animal activity within many ecosystems globally, attracting scavengers that rely on this food source. However, many scavengers are invasive species whose impacts on scavenging food webs and ecosystem processes linked to decomposition are poorly understood. Here, we use Australia as a case study to review the extent of scavenging by invasive species that have colonised the continent since European settlement, identify the factors that influence their use of carcasses, and highlight the lesser-known ecological effects of invasive scavengers. From 44 published studies we identified six invasive species from 48 vertebrates and four main groups of arthropods (beetles, flies, ants and wasps) that scavenge. Invasive red foxes (Vulpes vulpes), domestic dogs (Canis familiaris), feral pigs (Sus scrofa), black rats (Rattus rattus) and feral cats (Felis catus) were ranked as highly common vertebrate scavengers. Invasive European wasps (Vespula germanica) are also common scavengers where they occur. We found that the diversity of native vertebrate scavengers is lower when the proportion of invasive scavengers is higher. We highlight that the presence of large (apex) native vertebrate scavengers can decrease rates of scavenging by invasive species, but that invasive scavengers can monopolise carcass resources, outcompete native scavengers, predate other species around carcass resources and even facilitate invasion meltdowns that affect other species and ecological processes including altered decomposition rates and nutrient cycling. Such effects are likely to be widespread where invasive scavengers occur and suggest a need to determine whether excessive or readily available carcass loads are facilitating or exacerbating the impacts of invasive species on ecosystems globally.

Fear of large carnivores amplifies human-caused mortality for mesopredators.

The challenge that large carnivores face in coexisting with humans calls into question their ability to carry out critical ecosystem functions such as mesopredator suppression outside protected areas. In this study, we examined the movements and fates of mesopredators and large carnivores across rural landscapes characterized by substantial human influences. Mesopredators shifted their movements toward areas with twofold-greater human influence in regions occupied by large carnivores, indicating that they perceived humans to be less of a threat. However, rather than shielding mesopredators, human-caused mortality was more than three times higher than large carnivore-caused mortality. Mesopredator suppression by apex predators may thus be amplified, rather than dampened, outside protected areas, because fear of large carnivores drives mesopredators into areas of even greater risk from human super predators.

Incidental nest predation in freshwater turtles: inter- and intraspecific differences in vulnerability are explained by relative crypsis.

There has long been interest in the influence of predators on prey populations, although most predator-prey studies have focused on prey species that are targets of directed predator searching. Conversely, few have addressed depredation that occurs after incidental encounters with predators. We tested two predictions stemming from the hypothesis that nest predation on two sympatric freshwater turtle species whose nests are differentially prone to opportunistic detection-painted turtles (Chrysemys picta) and snapping turtles (Chelydra serpentina)-is incidental: (1) predation rates should be density independent, and (2) individual predators should not alter their foraging behavior after encountering nests. After monitoring nest survival and predator behavior following nest depredation over 2 years, we confirmed that predation by raccoons (Procyon lotor), the primary nest predators in our study area, matched both predictions. Furthermore, cryptic C. picta nests were victimized with lower frequency than more detectable C. serpentina nests, and nests of both species were more vulnerable in human-modified areas where opportunistic nest discovery is facilitated. Despite apparently being incidental, predation on nests of both species was intensive (57% for painted turtles, 84% for snapping turtles), and most depredations occurred within 1 day of nest establishment. By implication, predation need not be directed to affect prey demography, and factors influencing prey crypsis are drivers of the impact of incidental predation on prey. Our results also imply that efforts to conserve imperiled turtle populations in human-modified landscapes should include restoration of undisturbed conditions that are less likely to expose nests to incidental predators.

Snakebite Envenomation, Attitudes, and Behavior toward Snakes in Banten, Indonesia.

Snakes are commonly associated with feelings of anxiety or disgust, and snake conservation is often hindered by negative attitudes and perceptions. Although global snake populations are generally in decline, snakebite envenomation (SBE) continues to be recognized as a serious public health issue, particularly in rural areas of tropical and subtropical countries. Data on SBE, a neglected tropical disease, are lacking, and Indonesia, a hotspot of venomous snake diversity, has no snake bite reporting system. We analyzed 127 survey results in Banten, Indonesia with the aim of documenting SBE and exploring the relationships between respondents' experiences, attitudes, and behaviors toward snakes. Nine percent of respondents had experienced SBE, and knowledge of SBE incidents was associated with negative attitudes toward snake populations, with negative attitudes toward snakes associated with a higher likelihood of anti-conservation behavior. Women were more fearful than men, and women and those with lower education levels were more negative toward pythons (Malayopython reticulatus), suggesting that increased knowledge may aid in snake conservation efforts. Universally negative risk beliefs and attitudes toward venomous snakes indicate a need to reduce the threat of SBE in our study area.

Scavenging Effects of Large Canids.

Many large predators are also facultative scavengers that may compete with and depredate other species at carcasses. Yet, the ecological impacts of facultative scavenging by large predators, or their "scavenging effects," still receive relatively little attention in comparison to their predation effects. To address this knowledge gap, we comprehensively examine the roles played by, and impacts of, facultative scavengers, with a focus on large canids: the African wild dog (Lycaon pictus), dhole (Cuon alpinus), dingo (Canis dingo), Ethiopian wolf (Canis simensis), gray wolf (Canis lupus), maned wolf (Chrysocyon brachyurus), and red wolf (Canis rufus). Specifically, after defining facultative scavenging as use or usurpation of a carcass that a consumer has not killed, we (1) provide a conceptual overview of the community interactions around carcasses that can be initiated by facultative scavengers, (2) review the extent of scavenging by and the evidence for scavenging effects of large canids, (3) discuss external factors that may diminish or enhance the effects of large canids as scavengers, and (4) identify aspects of this phenomenon that require additional research attention as a guide for future work.

Predation landscapes influence migratory prey ecology and evolution.

Migratory prey experience spatially variable predation across their life cycle. They face unique challenges in navigating this predation landscape, which affects their perception of risk, antipredator responses, and resulting mortality. Variable and unfamiliar predator cues during migration can limit accurate perception of risk and migrants often rely on social information and learning to compensate. The energetic demands of migration constrain antipredator responses, often through context-dependent patterns. While migration can increase mortality, migrants employ diverse strategies to balance risks and rewards, including life history and antipredator responses. Humans interact frequently with migratory prey across space and alter both mortality risk and antipredator responses, which can scale up to affect migratory populations and should be considered in conservation and management.