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Anthropogenic impacts on wildlife behavior arise both from the immediate presence of people, which induces fear responses in many species, and the human footprint (i.e., landscape modification such as residential development), which affects animal movement and habitat use. Where both disturbance types co-occur, disentangling their impacts remains a challenge. Disturbance effects may interact such that species respond to increased human footprint by either reducing (habituation) or increasing (sensitization) avoidance of human presence. We experimentally manipulated perceived human presence, using playbacks of people talking, across a gradient of human footprint in California’s Santa Cruz Mountains and used camera traps to quantify the behavioral responses of bobcats (Lynx rufus), striped skunks (Mephitis mephitis), and Virginia opossums (Didelphis virginiana), mesopredators known to exhibit strong fear response to human presence but which vary in their use of developed areas. Bobcats and skunks reduced activity in response to human playbacks but showed no change in responsiveness to playbacks across the gradient of human footprint, suggesting that these species are similarly fearful of humans at all development levels tested. Opossums exhibited a significant interaction between human footprint and playback treatment such that reductions in activity level in response to human playbacks were strongest at higher levels of building density. Our results indicate that, rather than habituating to human presence, some mesopredators retain a strong fear of humans or become more fearful when inhabiting more developed areas. We suggest that consistently high responsiveness to immediate human presence may benefit mesopredators living in human-dominated landscapes by mitigating the risk of anthropogenic mortality.

Camera trap technology has galvanized the study of predator–prey ecology in wild animal communities by expanding the scale and diversity of predator–prey interactions that can be analysed. While observational data from systematic camera arrays have informed inferences on the spatiotemporal outcomes of predator–prey interactions, the capacity for observational studies to identify mechanistic drivers of species interactions is limited. Experimental study designs that utilize camera traps uniquely allow for testing hypothesized mechanisms that drive predator and prey behaviour, incorporating environmental realism not possible in the laboratory while benefiting from the distinct capacity of camera traps to generate large datasets from multiple species with minimal observer interference. However, such pairings of camera traps with experimental methods remain underutilized. We review recent advances in the experimental application of camera traps to investigate fundamental mechanisms underlying predator–prey ecology and present a conceptual guide for designing experimental camera trap studies. Only 9% of camera trap studies on predator–prey ecology in our review use experimental methods, but the application of experimental approaches is increasing. To illustrate the utility of camera trap-based experiments using a case study, we propose a study design that integrates observational and experimental techniques to test a perennial question in predator–prey ecology: how prey balance foraging and safety, as formalized by the risk allocation hypothesis. We discuss applications of camera trap-based experiments to evaluate the diversity of anthropogenic influences on wildlife communities globally. Finally, we review challenges to conducting experimental camera trap studies. Experimental camera trap studies have already begun to play an important role in understanding the predator–prey ecology of free-living animals, and such methods will become increasingly critical to quantifying drivers of community interactions in a rapidly changing world. We recommend increased application of experimental methods in the study of predator and prey responses to humans, synanthropic and invasive species, and other anthropogenic disturbances.

Developed landscapes are increasingly important movement habitat for many large carnivore populations, despite fragmentation and heightened anthropogenic risks. The availability of vegetation cover is a key factor mediating carnivore use of human-dominated landscapes. Restoring or modifying networks of vegetation patches may therefore provide an important tool for enhancing the connectivity value of developed areas, but requires understanding how vegetation patch networks are functionally linked by carnivore movement decisions, which occur at scales considerably finer than those typically addressed by connectivity analyses. We investigated the factors driving fine-scale movement decisions by pumas (Puma concolor) in fragmented habitats and applied our results to enhancing puma connectivity through human-dominated landscapes. We used high-resolution data on vegetation cover and puma locations from central California to model puma habitat selection at the scale of individual movements between vegetation patches. These results informed network-based connectivity models comparing the benefits of specific wildlife corridor restoration actions (e.g., revegetation). Puma movements between vegetation patches were driven by patch size, vegetation type, and spatial arrangement relative to sources of anthropogenic risk (buildings). Pumas avoided buildings but accepted higher building densities as patch area increased or inter-patch travel distances decreased. Connectivity modeling revealed that the strategic placement of vegetation patches can substantially reduce resistance to puma movement across an otherwise high resistance developed landscape by diversifying movement options. Our results reveal the factors mediating large carnivore use of human-dominated landscapes and provide a generalizable tool for increasing movement potential via the manipulation of vegetation cover.

International audience; Predation risk, the probability that a prey animal will be killed by a predator, is fundamental to theoretical and applied ecology. Predation risk varies with animal behavior and environmental conditions, yet attempts to understand predation risk in natural systems often ignore important ecological and environmental complexities, relying instead on proxies for actual risk such as predator-prey spatial overlap. Here we detail the ecological and environmental complexities driving disconnects between three stages of the predation sequence that are often assumed to be tightly linked: spatial overlap, encounters, and prey capture. Our review highlights several major sources of variability in natural predator-prey systems that lead to the decoupling of spatial overlap estimates from actual encounter rates (e.g., temporal activity patterns, predator and prey movement capacity, resource limitations) and that affect the probability of prey capture given encounter (e.g., predator hunger levels, temporal, topographic, and other environmental influences on capture success). Emerging technologies and statistical methods are facilitating a transition to a more spatiotemporally detailed, mechanistic understanding of predator-prey interactions, allowing for the concurrent examination of multiple stages of the predation sequence in mobile, free-ranging animals. We describe crucial applications of this new understanding to fundamental and applied ecology, highlighting opportunities to better integrate ecological contingencies into dynamic predator-prey models and to harness a mechanistic understanding of predator-prey interactions to improve targeting and effectiveness of conservation interventions.

When navigating heterogeneous landscapes, large carnivores must balance trade-offs between multiple goals, including minimizing energetic expenditure, maintaining access to hunting opportunities and avoiding potential risk from humans. The relative importance of these goals in driving carnivore movement likely changes across temporal scales, but our understanding of these dynamics remains limited. Here we quantified how drivers of movement and habitat selection changed with temporal grain for two large carnivore species living in human-dominated landscapes, providing insights into commonalities in carnivore movement strategies across regions. We used high-resolution GPS collar data and integrated step selection analyses to model movement and habitat selection for African lions Panthera leo in Laikipia, Kenya and pumas Puma concolor in the Santa Cruz Mountains of California across eight temporal grains, ranging from 5 min to 12 hr. Analyses considered landscape covariates that are related to energetics, resource acquisition and anthropogenic risk. For both species, topographic slope, which strongly influences energetic expenditure, drove habitat selection and movement patterns over fine temporal grains but was less important at longer temporal grains. In contrast, avoiding anthropogenic risk during the day, when risk was highest, was consistently important across grains, but the degree to which carnivores relaxed this avoidance at night was strongest for longer term movements. Lions and pumas modified their movement behaviour differently in response to anthropogenic features: lions sped up while near humans at fine temporal grains, while pumas slowed down in more developed areas at coarse temporal grains. Finally, pumas experienced a trade-off between energetically efficient movement and avoiding anthropogenic risk. Temporal grain is an important methodological consideration in habitat selection analyses, as drivers of both movement and habitat selection changed across temporal grain. Additionally, grain-dependent patterns can reflect meaningful behavioural processes, including how fitness-relevant goals influence behaviour over different periods of time. In applying multi-scale analysis to fine-resolution data, we showed that two large carnivore species in very different human-dominated landscapes balanced competing energetic and safety demands in largely similar ways. These commonalities suggest general strategies of landscape use across large carnivore species.

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.

Wetland restoration provides remarkable opportunities to understand vegetation dynamics and to inform success of future projects through rigorous restoration experiments. Salt marsh restoration typically focuses on physical factors such as sediment dynamics and elevation. Despite many demonstrations of strong top-down effects on salt marshes, the potential for consumers to affect salt marsh restoration projects has rarely been quantified. Recently, major restoration projects at the Elkhorn Slough National Estuarine Research Reserve in central California, USA provided an opportunity to examine how herbivory influences restoration success. We quantified the strength of consumer effects by comparing caged to uncaged plantings, and compared effects among plant species and sites. We used camera traps to detect which herbivores were most common and how their abundance varied spatially. Beyond characterizing consumer effects, we also tested management strategies for reducing negative effects of herbivory at the restoration sites, including caging, mowing, and acoustic playbacks of predator sounds. We found extremely strong consumer effects at sites with extensive stands of exotic forbs upland of the high marsh; uncaged restoration plants suffered heavy herbivory and high mortality, while most caged plants survived. Brush rabbits (Sylvilagus bachmani) were by far the most frequent consumers of these high marsh plants. Our work thus provides the first evidence of mammal consumers affecting salt marsh restoration success. Mowing of tall exotic forb cover adjacent to the marsh at one restoration site greatly reduced consumption, and nearly all monitored plantings survived at a second restoration site where construction had temporarily eliminated upland cover. Playbacks of predator sounds did not significantly affect restoration plantings, but restoration efforts in marsh communities vulnerable to terrestrial herbivory may benefit from concurrent restoration of predator communities in the upland habitats surrounding the marsh. A landscape approach is thus critical for recognizing linkages between terrestrial and marine vegetation.

Energetic demands and fear of predators are considered primary factors shaping animal behavior, and both are likely drivers of movement decisions that ultimately determine the spatial ecology of wildlife. Yet energetic constraints on movement imposed by the physical landscape have only been considered separately from those imposed by risk avoidance, limiting our understanding of how short-term movement decisions scale up to affect long-term space use. Here, we integrate the costs of both physical terrain and predation risk into a common currency, energy, and then quantify their effects on the short-term movement and long-term spatial ecology of a large carnivore living in a human-dominated landscape. Using high-resolution GPS and accelerometer data from collared pumas (Puma concolor), we calculated the short-term (i.e., 5-min) energetic costs of navigating both rugged physical terrain and a landscape of risk from humans (major sources of both mortality and fear for our study population). Both the physical and risk landscapes affected puma short-term movement costs, with risk having a relatively greater impact by inducing high-energy but low-efficiency movement behavior. The cumulative effects of short-term movement costs led to reductions of 29% to 68% in daily travel distances and total home range area. For male pumas, long-term patterns of space use were predominantly driven by the energetic costs of human-induced risk. This work demonstrates that, along with physical terrain, predation risk plays a primary role in shaping an animal's "energy landscape" and suggests that fear of humans may be a major factor affecting wildlife movements worldwide.

Understanding the behavioral responses of large carnivores to human activity in protected areas is important for conserving top predators. Roads and associated vehicle traffic have a range of impacts on wildlife, including mortality from vehicle collisions and behavioral changes from increasing traffic levels. Roads concentrate human activities and may be particularly impactful when located adjacent to high‐quality habitat for wildlife. However, people often overlook road impacts in protected areas because of relatively low road densities. From 1979 to 2017, annual visits to Yellowstone National Park increased from 1.9 to 4.1 million, with many visitors in the last 25 yr focusing on the opportunity to view wild wolves (Canis lupus) in their natural habitat from the roadway. To better understand how human activity interacts with landscape attributes and prey availability to shape wolf habitat use, we developed seasonal and diel‐specific step selection functions (SSF) for wolves. Wolves responded to increased human activity by using areas farther from roadways during the day and during peak visitation in summer. Prey availability, as estimated by an elk SSF, did not significantly alter habitat selection patterns by wolves. The strength of habitat selection in relation to roads varied among wolf packs. The most heavily viewed wolf packs exhibited less road avoidance, suggesting increased tolerance, which could lead to increased vulnerability to human harvest if they leave the park. Federal and state managers have implemented several measures to mitigate disturbance effects to wolves and curtail habituation. These results may inform adaptive management strategies that seek to continue to conserve natural wolf behavior.

Summary How animals respond to anthropogenic disturbances is a core component of conservation biology and how they respond to predators and competitors is equally of central importance to wildlife ecology. Camera traps have rapidly become a critical tool in wildlife research by providing a fully automated means of observing animals without needing an observer present, permitting data to be collected on rare or elusive species and infrequent events. Snapshots from camera traps revealing a species’ presence have been the principal data used to date to gauge behaviour; but, lacking experimental controls, such data permit only correlational analyses potentially open to confounding effects. Playback experiments provide a powerful means to directly test the behavioural responses of animals, enabling strong inferences and rigorous conclusions not subject to the potential confounds affecting the interpretation of snapshot data; the principal factor to date limiting the use of playback experiments being the need to have an observer present. We developed an Automated Behavioural Response system (ABR) comprising a custom-built motion-sensitive speaker system that can be paired with any commercially available camera trap, providing the means to conduct playback experiments directly testing the behavioural responses of any species that can be ‘caught’ on a camera trap. We describe field tests in Uganda, Canada and the USA, experimentally testing the effects of anthropogenic disturbances and interactions among large carnivores, in species as diverse as elephants, black bears, chimpanzees and cougars; experiments that would be completely infeasible without the ABR. We evaluate factors affecting the rate of successful data collection in the experiments in Uganda and Canada, and detail how we maximized the system's performance in the USA experiment. By integrating the power playback experiments provide to directly and rigorously test behavioural responses with the capacity camera trapping affords to study virtually any animal anywhere, the ABR can both greatly expand the range of research questions addressed by conservation biologists and wildlife ecologists and qualitatively improve the rigour of the resulting conclusions. We discuss various ways to optimize the ABR's performance in any circumstance, and the many novel research opportunities made available by this new methodology.

Domestic dogs are the most abundant large carnivore on the planet, and their ubiquity has led to concern regarding the impacts of dogs as predators of and competitors with native wildlife. If native large carnivores perceive dogs as threatening, impacts could extend to the community level by altering interactions between large carnivores and their prey. Dog impacts may be further exacerbated if these human-associated predators are also perceived as indicators of risk from humans. However, observational approaches used to date have led to ambiguity regarding the effects of dog presence on wildlife. We experimentally quantified dog impacts on the behavior of a native large carnivore, presenting playbacks of dog vocalizations to pumas in central California. We show that the perceived presence of dogs has minimal impacts on puma behavior at their kill sites, and is no more likely to affect total feeding time at kills than non-threatening controls. We previously demonstrated that pumas exhibit strong responses to human cues, and here show that perceived risk from human presence far exceeds that from dogs. Our results suggest that protected areas management policies that restrict dogs but permit human access may in some cases be of limited value for large carnivores.

Apex predators such as large carnivores can have cascading, landscape-scale impacts across wildlife communities, which could result largely from the fear they inspire, although this has yet to be experimentally demonstrated. Humans have supplanted large carnivores as apex predators in many systems, and similarly pervasive impacts may now result from fear of the human 'super predator'. We conducted a landscape-scale playback experiment demonstrating that the sound of humans speaking generates a landscape of fear with pervasive effects across wildlife communities. Large carnivores avoided human voices and moved more cautiously when hearing humans, while medium-sized carnivores became more elusive and reduced foraging. Small mammals evidently benefited, increasing habitat use and foraging. Thus, just the sound of a predator can have landscape-scale effects at multiple trophic levels. Our results indicate that many of the globally observed impacts on wildlife attributed to anthropogenic activity may be explained by fear of humans.

Human impacts on wildlife stem from both our footprint on the landscape and the presence of people in wildlife habitat. Each may influence wildlife at very different spatial and temporal scales, yet efforts to disentangle these two classes of anthropogenic disturbance in their effects on wildlife have remained limited, as have efforts to predict the spatial extent of human presence and its impacts independently of human footprint. We used camera trap data from a 1400-km2 grid spanning wildlands and residential development in central California to compare the effects of human presence (human detections on camera) and footprint (building density) on mammalian predators. We then developed a model predicting the spatial extent of human presence and its impacts across the broader landscape. Occupancy modeling and temporal activity analyses showed that human presence and footprint had non-equivalent and often opposing effects on wildlife. Larger predators (pumas Puma concolor, bobcats Lynx rufus, coyotes Canis latrans) were less active where human footprint was high but avoided high human presence temporally rather than spatially. Smaller predators (striped skunks Mephitis mephitis, Virginia opossums Didelphis virginiana) preferred developed areas but exhibited reduced activity where human presence was high. A spatial model, based on readily available landscape covariates (parking lots, trails, topography), performed well in predicting human activity outside of developed areas, and revealed high human presence even in remote protected areas that provide otherwise intact wildlife habitat. This work highlights the need to integrate multiple disturbance types when evaluating the impacts of anthropogenic activity on wildlife.

Co-occurrence with humans presents substantial risks for large carnivores, yet human-dominated landscapes are increasingly crucial to carnivore conservation as human land use continues to encroach on wildlife habitat. Flexibility in large carnivore behavior may be a primary factor mediating coexistence with people, allowing carnivores to calibrate their activity and habitat use to the perceived level of human risk. However, our understanding of how large carnivores adjust the timing and location of behaviors in response to variations in human activity across the landscape remains limited, impacting our ability to identify important habitat for populations outside of protected areas. Here we examine whether African lions (Panthera leo) modify their behavior and habitat use in response to risk of a human encounter, and whether behavior-specific habitat selection allows lions to access feeding opportunities in a human-dominated landscape in Kenya. We determined fine-scale behavioral states for lions using high-resolution GPS and accelerometer data, and then investigated behavior-specific habitat selection at multiple temporal and spatial scales (ranging from 15 minutes to 12 hours and from approximately 200 meters to several kilometers). We found that lions exhibit substantial differences in habitat selection with respect to humans based on behavioral state and time of day. During the day, when risk of human encounter is highest, lions avoided areas of high human use when resting, meandering, and feeding. However, lions specifically selected for habitat near people when feeding at night. Flexible habitat use by lions thus permits access to prey, which appear to concentrate in areas near humans. The importance of habitat near people for feeding was only apparent when analyses explicitly accounted for lion behavioral state and spatiotemporal scale, highlighting the necessity of incorporating such information when investigating human impacts on large carnivore habitat use. Our results support the contention that behavior-specific habitat selection promotes carnivore persistence in human-dominated landscapes, demonstrating the importance of considering not just whether but how large carnivores use habitat near humans when managing vulnerable populations.

Large carnivore behavioral responses to the cues of their competitors are rarely observed, but may mediate competition between these top predators. Playback experiments, currently limited to interactions involving group-living large carnivores, demonstrate that attending to cues indicative of the immediate presence of heterospecific competitors plays a substantial role in influencing competition among these species. Group-living species vocalize regularly to signal to one another, and competitors can readily “eavesdrop” on these acoustic cues. Solitary large carnivores also vocalize to conspecifics, but much less frequently, reducing the ease with which heterospecific competitors can eavesdrop. Eavesdropping could nonetheless play a substantive role in mediating competition among solitary large carnivores if the benefits of responding to the acoustic cues of heterospecific competitors (reducing risk or locating resources) are sufficiently large. Behavioral interactions between solitary large carnivore species are almost never observed, and there have been no experimental tests of their reactions to cues indicative of the immediate presence of other solitary large carnivores. We used an automated playback system to test the responses of a solitary large carnivore (black bear, Ursus americanus) to vocalizations of their similarly solitary competitor (cougar, Puma concolor), presenting both cougar and control vocalizations to free-living bears foraging along shorelines in British Columbia, Canada. Both mothers with cubs and solitary bears were significantly more likely to advance and vocalize toward cougar than control playbacks, mothers producing one or both of two distinct vocalizations and solitary bears producing just one. Cougars could either represent a potential risk to bears (particularly cubs), or a source of resources, as bears are known to regularly scavenge cougar kills. Our results are consistent with bears eavesdropping on cougars for both these reasons. As with group-living species, eavesdropping may be common among solitary large carnivores, and may be an important driver of competition between these species.

Large carnivores' fear of the human ‘super predator’ has the potential to alter their feeding behaviour and result in human-induced trophic cascades. However, it has yet to be experimentally tested if large carnivores perceive humans as predators and react strongly enough to have cascading effects on their prey. We conducted a predator playback experiment exposing pumas to predator (human) and non-predator control (frog) sounds at puma feeding sites to measure immediate fear responses to humans and the subsequent impacts on feeding. We found that pumas fled more frequently, took longer to return, and reduced their overall feeding time by more than half in response to hearing the human ‘super predator’. Combined with our previous work showing higher kill rates of deer in more urbanized landscapes, this study reveals that fear is the mechanism driving an ecological cascade from humans to increased puma predation on deer. By demonstrating that the fear of humans can cause a strong reduction in feeding by pumas, our results support that non-consumptive forms of human disturbance may alter the ecological role of large carnivores.

Medium-sized mammalian predators (i.e. mesopredators) on islands are known to have devastating effects on the abundance and diversity of terrestrial vertebrates. Mesopredators are often highly omnivorous, and on islands, may have access not only to terrestrial prey, but to marine prey as well, though impacts of mammalian mesopredators on marine communities have rarely been considered. Large apex predators are likely to be extirpated or absent on islands, implying a lack of top-down control of mesopredators that, in combination with high food availability from terrestrial and marine sources, likely exacerbates their impacts on island prey. We exploited a natural experiment--the presence or absence of raccoons (Procyon lotor) on islands in the Gulf Islands, British Columbia, Canada--to investigate the impacts that this key mesopredator has on both terrestrial and marine prey in an island system from which all native apex predators have been extirpated. Long-term monitoring of song sparrow (Melospiza melodia) nests showed raccoons to be the predominant nest predator in the Gulf Islands. To identify their community-level impacts, we surveyed the distribution of raccoons across 44 Gulf Islands, and then compared terrestrial and marine prey abundances on six raccoon-present and six raccoon-absent islands. Our results demonstrate significant negative effects of raccoons on terrestrial, intertidal, and shallow subtidal prey abundance, and point to additional community-level effects through indirect interactions. Our findings show that mammalian mesopredators not only affect terrestrial prey, but that, on islands, their direct impacts extend to the surrounding marine community.

Energy gain is thought to play a central role in prey selection by most foragers, but it may conflict with food theft avoidance and be constrained by undeveloped foraging skills. We investigated predation by the Glaucous-winged Gull (Larus glaucescens) on the ecologically important Ochre Sea Star (Pisaster ochraceus). We tested the hypothesis that Pisaster size selection by gulls was based on energetic profitability, defined as energy provided per unit handling time. We then examined the degree to which profitability interacts with intraspecific kleptoparasitism risk and age-related foraging efficiency (i.e., energy intake rate, prey capture success) to produce the patterns of prey choice observed in a natural setting. Behavioral observations of free-living gulls revealed moderate to high (32.5–91.6%) occurrences of Pisaster in gull diets. We used handling time data and bomb calorimetry to determine the relationship between Pisaster size and energetic profitability, which informed prey offer exp...

Biodiversity hotspots have been used extensively in setting conservation priorities for marine ecosystems. A recent Nature publication claims to have uncovered new latitudinal gradients in the evenness of reef communities and new reef hotspots based on functional diversity. Simulation models show that the purported evenness gradient is a mathematical inevitability of differences in species richness and detectability between vastly different marine ecosystems, namely ‘reefs’ in tropical, temperate, and polar regions. Constraints on evenness, along with disparity amongst communities in possible functional traits, cast doubt on the utility of global functional diversity comparisons for management of marine systems.

The pathogenic chytrid fungus, Batrachochytrium dendrobatidis, has been implicated as the main driver of many enigmatic amphibian declines in neotropical sites at high elevation. Batrachochytrium dendrobatidis is thought to be a waterborne pathogen limited by temperature, and the extent to which it persists and causes disease in amphibians at lower elevations in the neotropics is not known. It also is unclear by what mechanism(s) B. dendrobatidis has emerged as a pathogenic organism. To test whether B. dendrobatidis is limited by elevation in Panamá, we sought to determine the prevalence and intensity of B. dendrobatidis in relation to anuran abundance and diversity using quantitative PCR (qPCR) analyses. Sites were situated at varying elevations, from 45 to 1215 m, and were at varying stages of epizootic amphibian decline, including pre-epizootic, mid-epizootic, 2 years post-epizootic, and 10 years post-epizootic. Batrachochytrium dendrobatidis was found in all sites regardless of elevation or stage of epizootic decline. Levels of prevalence and infection intensity were comparable across all sites except at the mid-epizootic site, where both prevalence and intensity were significantly higher than at other sites. Symptoms of chytridiomycosis and corresponding declines in amphibian populations were variably seen at all elevations along a post-epizootic gradient. Because it is inherently difficult to prove a negative proposition, it can neither be proven that B. dendrobatidis is truly not present where it is not detected nor proven that it is only recently arrived where it is detected. Thus, there will always be doubts about whether B. dendrobatidis is enzootic or invasive. In any case, our results, coupled with current knowledge, suggest most clearly that the disease, chytridiomycosis, may be novel and invasive, and that the pathogen, B. dendrobatidis either is, or is becoming, globally ubiquitous.

The fear large carnivores inspire, independent of their direct killing of prey, may itself cause cascading effects down food webs potentially critical for conserving ecosystem function, particularly by affecting large herbivores and mesocarnivores. However, the evidence of this has been repeatedly challenged because it remains experimentally untested. Here we show that experimentally manipulating fear itself in free-living mesocarnivore (raccoon) populations using month-long playbacks of large carnivore vocalizations caused just such cascading effects, reducing mesocarnivore foraging to the benefit of the mesocarnivore's prey, which in turn affected a competitor and prey of the mesocarnivore's prey. We further report that by experimentally restoring the fear of large carnivores in our study system, where most large carnivores have been extirpated, we succeeded in reversing this mesocarnivore's impacts. We suggest that our results reinforce the need to conserve large carnivores given the significant “ecosystem service” the fear of them provides., Top predators may indirectly influence ecological processes through fear-induced behavioural changes in their prey. By experimentally manipulating this ‘landscape of fear', Suraci et al. show that fear of large carnivores in a mesopredator can cause cascading effects down the food web that benefit its prey.

The presence of large carnivores can affect lower trophic levels by suppressing mesocarnivores and reducing their impacts on prey. The mesopredator release hypothesis therefore predicts prey abundance will be higher where large carnivores are present, but this prediction assumes limited dietary overlap between large and mesocarnivores. Where dietary overlap is high, e.g., among omnivorous carnivore species, or where prey are relatively easily accessible, the potential exists for large and mesocarnivores to have redundant impacts on prey, though this possibility has not been explored. The intertidal community represents a potentially important but poorly studied resource for coastal carnivore populations, and one for which dietary overlap between carnivores may be high. To evaluate usage of the intertidal community by coastal carnivores and the potential for redundancy between large and mesocarnivores, we surveyed (i) intertidal prey abundance (crabs and fish) and (ii) the abundance and activity of large carnivores (predominantly black bears) and mesocarnivores (raccoons and mink) in an area with an intact carnivore community in coastal British Columbia, Canada. Overall carnivore activity was strongly related to intertidal prey availability. Notably, this relationship was not contingent on carnivore species identity, suggestive of redundancy-high intertidal prey availability was associated with either greater large carnivore activity or greater mesocarnivore activity. We then compared intertidal prey abundances in this intact system, in which bears dominate, with those in a nearby system where bears and other large carnivores have been extirpated, and raccoons are the primary intertidal predator. We found significant similarities in intertidal species abundances, providing additional evidence for redundancy between large (bear) and mesocarnivore (raccoon) impacts on intertidal prey. Taken together, our results indicate that intertidal prey shape habitat use and competition among coastal carnivores, and raise the interesting possibility of redundancy between mesocarnivores and large carnivores in their role as intertidal top predators.

Predators kill prey thereby affecting prey survival and, in the traditional top-down view of predator limitation, that is their sole effect. Bottom-up food limitation alters the physiological condition of individuals affecting both fecundity and survival. Predators of course also scare prey inducing anti-predator defences that may carry physiological costs powerful enough to reduce prey fecundity and survival. Here, we consider whether measuring physiology can be used as a tool to unambiguously diagnose predation risk effects. We begin by providing a review of recent papers reporting physiological effects of predation risk. We then present a conceptual framework describing the pathways by which predators and food can affect prey populations and give an overview of predation risk effects on demography in various taxa. Because scared prey typically eat less the principal challenge we see will be to identify measures that permit us to avoid mistaking predator-induced reductions in food intake for absolute food shortage. To construct an effective diagnostic toolkit we advocate collecting multiple physiological measures and utilizing multivariate statistical procedures. We recommend conducting two-factor predation risk × food manipulations to identify those physiological effects least likely to be mistaken for responses to bottom-up food limitation. We suggest there is a critical need to develop a diagnostic tool that can be used when it is infeasible to experimentally test for predation risk effects on demography, as may often be the case in wildlife conservation, since failing to consider predation risk effects may cause the total impact of predators to be dramatically underestimated.

By suppressing mesocarnivore foraging, the fear large carnivores inspire can be critical to mitigating mesocarnivore impacts. Where large carnivores have declined, mesocarnivores may quantitatively increase foraging, commensurate with reductions in fear. The extirpation of large carnivores may further exacerbate mesocarnivore impacts by causing qualitative changes in mesocarnivore behavior. Error management theory suggests that, where predators are present, prey should be biased towards over-responsiveness to predator cues, abandoning foraging in response to both predator cues and benign stimuli mistaken for predator cues (false-positives). Where predators are absent, prey may avoid these foraging costs by becoming unresponsive (naïve) to both predator cues and false-positives. If naiveté occurs in mesocarnivores where large carnivores have been extirpated, it could substantively exacerbate their impacts, as "fearless" mesocarnivores may engage in virtually unrestricted foraging. We tested the naiveté of raccoons (Procyon lotor) to extirpated large carnivores in the context of a larger experiment demonstrating that fear of large carnivores can mediate mesocarnivore impacts. Raccoon responsiveness to playbacks of their extirpated large carnivore predators (cougars, Puma concolor; bears, Ursus americanus) was significantly less than to the only extant large carnivore predator (dogs), and was no greater than to non-predators ("seals"; Phoca vitulina, Eumetopias jubatus). Raccoons failed to recognize their now extirpated predators as threatening, spending as much time foraging as when hearing non-predators, which we estimate has substantive impacts, based on results from the larger experiment. We discuss the potentially powerful role of "fearlessness" in exacerbating mesocarnivore impacts in systems where large carnivores have been lost.

The fear (perceived predation risk) large carnivores inspire in mesocarnivores can affect ecosystem structure and function, and loss of the “landscape of fear” large carnivores create adds to concerns regarding the worldwide loss of large carnivores. Fear of humans has been proposed to act as a substitute but new research identifies humans as a “super predator” globally far more lethal to mesocarnivores, and thus presumably far more frightening. Although much of the world now consists of human-dominated landscapes there remains relatively little research regarding how behavioral responses to humans affecttrophic networks, to the extent that no study has yet experimentally tested the relative fearfulness mesocarnivores demonstrate in reaction to humans versus nonhuman predators. Badgers (Meles meles) in Britain are a model mesocarnivore insofar as they no longer need fear native large carnivores (bears, Ursus arctos; wolves, Canis lupus) and now perhaps fear humans more. We tested the fearfulness badgers demonstrated to audio playbacks of extant (dog) andextinct (bear and wolf) large carnivores, and humans, by assaying the suppression of foragingbehavior. Hearing humans affected all of: latency to feed, vigilance, foraging time, number of feeding visits, and number of badgers feeding. Hearing dogs and bears had far lesser effects on latency to feed, and hearing wolves had no effects. Our results indicate fear of humans evidently cannot substitute for the fear large carnivores inspire in mesocarnivores because humansare perceived as far more frightening, which we discuss in light of the recovery of large carnivores in human-dominated landscapes.

Managing vertebrate pests is a global conservation challenge given their undesirable socio-ecological impacts. Pest management often focuses on the 'average' individual, neglecting individual-level behavioural variation ('personalities') and differences in life histories. These differences affect pest impacts and modify attraction to, or avoidance of, sensory cues. Strategies targeting the average individual may fail to mitigate damage by 'rogues' (individuals causing disproportionate impact) or to target 'recalcitrants' (individuals avoiding standard control measures). Effective management leverages animal behaviours that relate primarily to four core motivations: feeding, fleeing, fighting, and fornication. Management success could be greatly increased by identifying and exploiting individual variation in motivations. We provide explicit suggestions for cue-based tools to manipulate these four motivators, thereby improving pest management outcomes.