Diel predator activity drives a dynamic landscape of fear

Cats and dogs: A mesopredator navigating risk and reward provisioned by an apex predator

Successfully perceiving risk and reward is fundamental to the fitness of an animal, and can be achieved through a variety of perception tactics. For example, mesopredators may "directly" perceive risk by visually observing apex predators, or may "indirectly" perceive risk by observing habitats used by predators. Direct assessments should more accurately characterize the arrangement of risk and reward; however, indirect assessments are used more frequently in studies concerning the response of GPS-marked animals to spatiotemporally variable sources of risk and reward. We investigated the response of a mesopredator to the presence of risk and reward created by an apex predator, where risk and reward likely vary in relative perceptibility (i.e., degree of being perceptible). First, we tested whether coyotes (Canis latrans) use direct or indirect assessments to navigate the presence of mountain lions (Puma concolor; risk) and kills made by mountain lions (reward) in an area where coyotes were a common prey item for mountain lions. Second, we assessed the behavioral response of coyotes to direct encounters with mountain lions. Third, we evaluated spatiotemporal use of carrion by coyotes at kills made by mountain lions. Indirect assessments generally outperformed direct assessments when integrating analyses into a unified framework; nevertheless, our ability to detect direct perception in navigating to mountain lion kills was likely restricted by scale and sampling limitations (e.g., collar fix rates, unsampled kill sites). Rather than responding to the risk of direct encounters with mountain lions, coyotes facilitated encounters by increasing their movement rate, and engaged in risky behavior by scavenging at mountain lion kills. Coyotes appear to mitigate risk by using indirect perception to avoid mountain lions. Our predator-predator interactions and insights are nuanced and counter to the conventional predator-prey systems that have generated much of the predation risk literature.

Sampling bias exaggerates a textbook example of a trophic cascade

Understanding trophic cascades in terrestrial wildlife communities is a major challenge because these systems are difficult to sample properly. We show how a tradition of non-random sampling has confounded this understanding in a textbook system (Yellowstone National Park) where carnivore [Canis lupus (wolf)] recovery is associated with a trophic cascade involving changes in herbivore [Cervus canadensis (elk)] behaviour and density that promote plant regeneration. Long-term data indicate a practice of sampling only the tallest young plants overestimated regeneration of overstory aspen (Populus tremuloides) by a factor of 4-7 compared to random sampling because it favoured plants taller than the preferred browsing height of elk and overlooked non-regenerating aspen stands. Random sampling described a trophic cascade, but it was weaker than the one that non-random sampling described. Our findings highlight the critical importance of basic sampling principles (e.g. randomisation) for achieving an accurate understanding of trophic cascades in terrestrial wildlife systems.

Spatial compartmentalization: A nonlethal predator mechanism to reduce parasite transmission between prey species

Predators can modulate disease transmission within prey populations by influencing prey demography and behavior. Predator-prey dynamics can involve multiple species in heterogeneous landscapes; however, studies of predation on disease transmission rarely consider the role of landscapes or the transmission among diverse prey species (i.e., spillover). We used high-resolution habitat and movement data to model spillover risk of the brainworm parasite (Parelaphostrongylus tenuis) between two prey species [white-tailed deer (Odocoileus virginianus) and moose (Alces alces)], accounting for predator [gray wolf (Canis lupus)] presence and landscape configuration. Results revealed that spring migratory movements of cervid hosts increased parasite spillover risk from deer to moose, an effect tempered by changes in elevation, land cover, and wolf presence. Wolves induced host-species segregation, a nonlethal mechanism that modulated disease emergence by reducing spatiotemporal overlap between infected and susceptible prey, showing that wildlife disease dynamics may change with landscape disturbance and the loss of large carnivores.

Winter Tick Burdens for Moose Are Positively Associated With Warmer Summers and Higher Predation Rates

Climate change is expected to modify host-parasite interactions which is concerning because parasites are involved in most food-web links, and parasites have important influences on the structure, productivity and stability of communities and ecosystems. However, the impact of climate change on host–parasite interactions and any cascading effects on other ecosystem processes has received relatively little empirical attention. We assessed host-parasite dynamics for moose (Alces alces) and winter ticks (Dermacentor albipictus) in Isle Royale National Park over a 19-year period. Specifically, we monitored annual tick burdens for moose (estimated from hair loss) and assessed how it covaried with several aspects of seasonal climate, and non-climatic factors, such as moose density, predation on hosts by wolves (Canis lupus) and wolf abundance. Summer temperatures explained half the interannual variance in tick burden with tick burden being greater following hotter summers, presumably because warmer temperatures accelerate the development of tick eggs and increase egg survival. That finding is consistent with the general expectation that warmer temperatures may promote higher parasite burdens. However, summer temperatures are warming less rapidly than other seasons across most regions of North America. Therefore, tick burdens seem to be primarily associated with an aspect of climate that is currently exhibiting a lower rate of change. Tick burdens were also positively correlated with predation rate, which could be due to moose exhibiting risk-sensitive habitat selection (in years when predation risk is high) in such a manner as to increases the encounter rate with questing tick larvae in autumn. However, that positive correlation could also arise if high parasite burdens make moose more vulnerable to predators or because of some other density-dependent process (given that predation rate and moose density are highly correlated). Overall, these results provide valuable insights about interrelationships among climate, parasites, host/prey, and predators.

Lassiter E, Massey A, Roberts CP, T. Veon J. Nine-banded armadillo (Dasypus novemcinctus) activity patterns are influenced by human activity

As the human footprint upon the landscape expands, wildlife seeking to avoid human contact are losing the option of altering their spatial distribution and instead are shifting their daily activity patterns to be active at different times than humans. In this study, we used game cameras to evaluate how human development and activity were related to the daily activity patterns of the nine-banded armadillo (Dasypus novemcinctus) along an urban to rural gradient in Arkansas, USA during the winter of 2020-2021. We found that armadillos had substantial behavioral plasticity in regard to the timing of their activity patterns; >95% of armadillo activity was nocturnal at six of the study sites, whereas between 30% and 60% of activity occurred during the day at three other sites. The likelihood of diurnal armadillo activity was best explained by the distance to downtown Fayetteville (the nearest population center) and estimated ambient sound level (both indices of human activity) with armadillos being most active during the day at quiet sites far from Fayetteville. Furthermore, armadillo activity occurred later during the night period (minutes after sunset) at sites near downtown and with higher anthropogenic sound. Anecdotal evidence suggests that the observed activity shift may be in response to not only human activity but also the presence of domestic dogs. Our results provide further evidence that human activity has subtle nonlethal impacts on even common, widespread wildlife species. Because armadillos have low body temperatures and basal metabolism, being active during cold winter nights likely has measurable fitness costs. Nature reserves near human population centers may not serve as safe harbors for wildlife as we intend, and managers could benefit from considering these nonlethal responses in how they manage recreation and visitation in these natural areas.

Contrasting patterns of risk from human and non-human predators shape temporal activity of prey

Spatiotemporal variation in predation risk arises from interactions between landscape heterogeneity, predator densities and predator hunting mode, generating landscapes of fear for prey species that can have important effects on prey behaviour and ecosystem dynamics. As widespread apex predators, humans present a significant source of risk for hunted animal populations. Spatiotemporal patterns of risk from hunters can overlap or contrast with patterns of risk from other predators. Human infrastructure can also reshape spatial patterns of risk by facilitating or impeding hunter or predator movement, or deterring predators that are themselves wary of humans. We examined how anthropogenic and natural landscape features interact with hunting modes of rifle hunters and mountain lions Puma concolor to generate spatiotemporal patterns of risk for their primary prey. We explored the implications of human-modified landscapes of fear for Columbian black-tailed deer Odocoileus hemionus columbianus in Mendocino County, California. We used historical harvest records, hunter GPS trackers and camera trap records of mountain lions to model patterns of risk for deer. We then used camera traps to examine deer spatial and temporal activity patterns in response to this variation in risk. Hunters and mountain lions exhibited distinct, contrasting patterns of spatiotemporal activity. Risk from rifle hunters, who rely on long lines of sight, was highest in open grasslands and near roads and was confined to the daytime. Risk from mountain lions, an ambush predator, was highest in dense shrubland habitat, farther from developed areas, and during the night and crepuscular periods. Areas of human settlement provided a refuge from both hunters and mountain lions. We found no evidence that deer avoided risk in space at the scale of our observations, but deer adjusted their temporal activity patterns to reduce the risk of encounters with humans and mountain lions in areas of higher risk. Our study demonstrates that interactions between human infrastructure, habitat cover and predator hunting mode can result in distinct spatial patterns of predation risk from hunters and other predators that may lead to trade-offs for prey species. However, distinct diel activity patterns of predators may create vacant hunting domains that reduce costly trade-offs for prey. Our study highlights the importance of temporal partitioning as a mechanism of predation risk avoidance.

Temporal scale of habitat selection for large carnivores: Balancing energetics, risk and finding prey

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.

Past agricultural land use affects multiple facets of ungulate antipredator behavior

Antipredator behavior affects prey fitness, prey demography, and the strength of ecological interactions. Although predator-prey interactions increasingly occur in habitats that experience multiple forms of human-generated disturbance, it is unclear how different forms of disturbance might affect antipredator behavior. Fire is a contemporary disturbance that has dramatic effects on terrestrial habitats. Such habitats may have also experienced past disturbances, like agricultural land use, that leave lasting legacies on habitat structure (e.g., overstory and understory composition). It is unclear how these past and present disturbances affect the use of different antipredator behaviors, like temporal avoidance and vigilance. We examined whether variation in disturbance regimes generates differences in ungulate antipredator behavior by using cameras to measure white-tailed deer vigilance and activity time across 24 longleaf pine woodlands that vary in past land use and contemporary fire regime. Regardless of land-use history, woodlands with high fire frequencies had 4 times less vegetation cover than low-fire woodlands, generating riskier habitats for deer; however, deer responded to fire with different antipredator strategies depending on land-use history. In nonagricultural woodlands, fire affected deer activity time such that activity was nocturnal in low-fire woodlands and crepuscular in high-fire woodlands. In post-agricultural woodlands, fire affected vigilance and not activity time such that deer were more vigilant in high-fire woodlands than in low-fire woodlands. These results suggest that ungulate antipredator behavior may vary spatially depending on past land use and contemporary fire regime, and such disturbances may generate “landscapes of fear” that persist for decades after agricultural use.

Running away or running to? Do prey make decisions solely based on the landscape of fear or do they also include stimuli from a landscape of safety?

Predator-prey interactions are a key part of ecosystem function, and non-consumptive effects fall under the landscape of fear theory. Under the landscape of fear, the antipredator responses of prey are based on the spatial and temporal distribution of predatory cues in the environment. However, the aversive stimuli (fear) are not the only stimuli prey can utilize when making behavioral decisions. Prey might also be using attractive stimuli that represent safety to guide decision making. Using a novel, orthogonal design, we were able to spatially separate aversive and attractive stimuli to determine whether prey are utilizing safety cues to navigate their environment. Crayfish Faxonius rusticus were placed in the center of a behavioral arena. Aversive stimuli of either predatory bass Micropterus salmoides cues or conspecific alarm cues increased along the x-axis of the behavioral arena. Safety cues (shelters) increased along the y-axis by decreasing the number of shelter openings in this direction. Crayfish were allowed two phases to explore the arena: one without the fearful stimuli and one with the stimuli. Linear mixed models were conducted to determine whether movement behaviors and habitat utilization were affected by the phase of the trial and the type of aversive stimuli. Crayfish responded more strongly to alarm cues than to fear cues, with only alarm cues significantly impacting habitat utilization. When responding to alarm cues, crayfish used safety cues as well as fear cues to relocate themselves within the arena. Based on these results, we argue that crayfish utilize a landscape of safety in conjunction with a landscape of fear when navigating their environment.

The Cognitive Ecology of Animal Movement: Evidence From Birds and Mammals

Cognition, defined as the processes concerned with the acquisition, retention and use of information, underlies animals’ abilities to navigate their local surroundings, embark on long-distance seasonal migrations, and socially learn information relevant to movement. Hence, in order to fully understand and predict animal movement, researchers must know the cognitive mechanisms that generate such movement. Work on a few model systems indicates that most animals possess excellent spatial learning and memory abilities, meaning that they can acquire and later recall information about distances and directions among relevant objects. Similarly, field work on several species has revealed some of the mechanisms that enable them to navigate over distances of up to several thousand kilometers. Key behaviors related to movement such as the choice of nest location, home range location and migration route are often affected by parents and other conspecifics. In some species, such social influence leads to the formation of aggregations, which in turn may lead to further social learning about food locations or other resources. Throughout the review, we note a variety of topics at the interface of cognition and movement that invite further investigation. These include the use of social information embedded in trails, the likely important roles of soundscapes and smellscapes, the mechanisms that large mammals rely on for long-distance migration, and the effects of expertise acquired over extended periods.

Behavioral effects of wolf presence on moose habitat selection: testing the landscape of fear hypothesis in an anthropogenic landscape

Landscape of fear refers to the spatial variation in prey perception of predation risk, that under certain conditions, may lead to changes in their behavior. Behavioral responses of prey in relation to large carnivore predation risk have mainly been conducted in areas with low anthropogenic impact. We used long-term data on the distribution of moose in different habitat types in a system characterized by intensive management of all three trophic levels (silviculture, harvest of wolves and moose) to study effects on moose habitat selection resulting from the return of an apex predator, the wolf. We assumed that coursing predators such as wolves will cause an increased risk for moose in some habitat types and tested the hypotheses that moose will avoid open or young forest habitats following wolf establishment. After wolf recolonization, moose reduced their use of one type of open habitat (bog) but there was neither change in the use of the other open habitat type (clear-cut), nor in their use of young forest. Wolf establishment did not influence the use of habitat close to dense habitat when being in open habitats. Thus, the effect of wolves varied among habitat types and there was no unidirectional support for a behavioral effect of wolves' establishment on moose habitat use. Human-driven habitat heterogeneity, concentration of moose forage to certain habitat types, and the effects of a multiple predator guild on moose may all contribute to the results found. We conclude that the landscape of fear is likely to have weak ecological effects on moose in this system.

A role for lakes in revealing the nature of animal movement using high dimensional telemetry systems

Movement ecology is increasingly relying on experimental approaches and hypothesis testing to reveal how, when, where, why, and which animals move. Movement of megafauna is inherently interesting but many of the fundamental questions of movement ecology can be efficiently tested in study systems with high degrees of control. Lakes can be seen as microcosms for studying ecological processes and the use of high-resolution positioning systems to triangulate exact coordinates of fish, along with sensors that relay information about depth, temperature, acceleration, predation, and more, can be used to answer some of movement ecology's most pressing questions. We describe how key questions in animal movement have been approached and how experiments can be designed to gather information about movement processes to answer questions about the physiological, genetic, and environmental drivers of movement using lakes. We submit that whole lake telemetry studies have a key role to play not only in movement ecology but more broadly in biology as key scientific arenas for knowledge advancement. New hardware for tracking aquatic animals and statistical tools for understanding the processes underlying detection data will continue to advance the potential for revealing the paradigms that govern movement and biological phenomena not just within lakes but in other realms spanning lands and oceans.

Landscape of stress: Tree mortality influences physiological stress and survival in a native mesocarnivore

Climate change and anthropogenic modifications to the landscape can have both positive and negative effects on an animal. Linking landscape change to physiological stress and fitness of an animal is a fundamental tenet to be examined in applied ecology. Cortisol is a glucocorticoid hormone that can be used to indicate an animal's physiological stress response. In the Sierra Nevada Mountains of California, fishers (Pekania pennanti) are a threatened mesocarnivore that have been subjected to rapid landscape changes due to anthropogenic modifications and tree mortality related to a 4-year drought. We measured cortisol concentrations in the hair of 64 fishers (41 females, 23 males) captured and radio-collared in the Sierra National Forest, California. We addressed two main questions: (1) Is the physiological stress response of fishers influenced by anthropogenic factors, habitat type, canopy cover, and tree mortality due to drought in their home range? (2) Does the physiological stress response influence survival, reproduction, or body condition? We examined these factors within a fisher home range at 3 scales (30, 60, 95% isopleths). Using model selection, we found that tree mortality was the principle driver influencing stress levels among individual fishers with female and male fishers having increasing cortisol levels in home ranges with increasing tree mortality. Most importantly, we also found a link between physiological stress and demography where female fishers with low cortisol levels had the highest annual survival rate (0.94), whereas females with medium and high cortisol had lower annual survival rates, 0.78 and 0.81, respectively. We found no significant relationships between cortisol levels and body condition, male survival, or litter size. We concluded that tree mortality related to a 4-year drought has created a "landscape of stress" for this small, isolated fisher population.

Fear of large carnivores is tied to ungulate habitat use: evidence from a bifactorial experiment

The fear large carnivores inspire in large ungulates has been argued to have cascading effects down food webs. However, a direct link between ungulate habitat use and their fear of large carnivores has not been experimentally tested. To fill this critical gap, we conducted a bi-factorial experiment in an African savanna. We removed shrub cover and broadcast large carnivore vocalizations (leopard, hyena, dog) or non-threatening control vocalizations in both experimentally cleared and shrubby control sites. We recorded the proactive (frequency of visitation) and reactive (fleeing or vigilance) responses of multiple prey (impala, warthog, nyala and bushbuck). Critically, we found a significant proactive-reactive interaction. Ungulates were 47% more likely to run after hearing a predator vocalization in shrubby control sites than experimental clearings, demonstrating that ungulates perceived less fear from large carnivores in open habitat (clearings). Consistent with this finding, ungulates visited clearings 2.4 times more often than shrubby control sites and visited shrubby control sites less often at night, when large carnivores are most active. Combined with results from previous experiments demonstrating that the disproportionate use of available habitats by large ungulates can alter ecosystem properties, our experiment provides critical evidence that the fear large carnivores inspire in large ungulates can cause trophic cascades.

American martens use vigilance and short-term avoidance to navigate a landscape of fear from fishers at artificial scavenging sites

Where two sympatric species compete for the same resource and one species is dominant, there is potential for the subordinate species to be affected through interference competition or energetic costs of avoiding predation. Fishers (Pekania pennanti) and American martens (Martes americana) often have high niche overlap, but fishers are considered dominant and potentially limiting to martens. We observed presence and vigilance of fishers and martens at winter carcass sites using remote cameras in Michigan, USA, to test the hypothesis that interference competition from fishers creates a landscape of fear for martens. Within winters, fishers co-occupied 78–88% of sites occupied by martens, and martens co-occupied 79–88% of sites occupied by fishers. Fishers displaced martens from carcasses during 21 of 6117 marten visits, while martens displaced fishers during 0 of 1359 fisher visits. Martens did not alter diel activity in response to fisher use of sites. Martens allocated 37% of time to vigilance compared to 23% for fishers, and martens increased vigilance up to 8% at sites previously visited by fishers. Fishers increased vigilance by up to 8% at sites previously visited by martens. Our results indicate that fishers were dominant over martens, and martens had greater baseline perception of risk than fishers. However, fishers appeared to be also affected as the dominant competitor by putting effort into scanning for martens. Both species appeared widespread and common in our study area, but there was no evidence that fishers spatially or temporally excluded martens from scavenging at carcasses other than occasional short-term displacement when a fisher was present. Instead, martens appeared to mitigate risk from fishers by using vigilance and short-term avoidance. Multiple short-term anti-predator behaviors within a landscape of fear may facilitate coexistence among carnivore species.

The role of hunting on Sapajus xanthosternos' landscape of fear in the Atlantic Forest, Brazil

Habitats with spatial variation in food availability, predation risk, and hunting pressure allow us to study how animals resolve the trade-off between food searching and predator avoidance. We investigated the influence of food availability, predation risk, and the perceived predation risk on habitat use by a primate living under high hunting pressure, the yellow-breasted capuchin monkeys, Sapajus xanthosternos, at Una Biological Reserve (ReBio Una). We hypothesized that the hunting pressure occurring in the capuchins' home range would favor predator avoidance to the detriment of searching for food. We characterized a set of covariates related to resource availability (fruit and invertebrate biomasses, feeding on dispersed and clumped food items, sleeping sites), perceived predation risk (alarm calls given to terrestrial and aerial predators, silent group movement, and vigilance behavior), and actual predation risk (evidence of hunting) and estimated their effects on how one group of capuchin monkeys uses its habitat. The group divides its time among three major forest types within their home range: agroforest, mature, and secondary. Our results suggest that the actual and perceived risk of hunting by humans, as well as the perceived predation risk by both terrestrial and aerial predators, were significant determinants of capuchin monkeys' space use. Yellow-breasted capuchin monkeys' space use was negatively related to the risk of hunting by humans (actual evidence and silent behavior), the perceived risk of predation by both aerial and terrestrial predators, and the presence of sleeping sites. Capuchin monkeys' use of space was not related to the biomass of fruits in the habitat, and the biomass of invertebrates had a very low positive effect. We confirmed our prediction that in a habitat with high hunting pressure, the risk of predation, both perceived and actual, had a more significant impact on how yellow-breasted capuchins used space than did food availability.

Sum of fears among intraguild predators drives the survival of green sea turtle (Chelonia mydas) eggs

Ecologists have long theorized that apex predators stabilize trophic systems by exerting a net protective effect on the basal resource of a food web. Although experimental and observational studies have borne this out, it is not always clear what behavioural mechanisms among the trophically connected species are responsible for this stability. Fear of intraguild predation is commonly identified as one such mechanism in models and mesocosm studies, but empirical evidence in natural systems remains limited, as the complexity of many trophic systems renders detailed behavioural studies of species interactions challenging. Here, we combine long-term field observations of a trophic system in nature with experimental behavioural studies of how all the species in this system interact, in both pairs and groups. The results demonstrate how an abundant, sessile and palatable prey item (sea turtle eggs, Chelonia mydas) survives when faced by three potential predators that all readily eat eggs: an apex predator (the stink ratsnake, Elaphe carinata) and two mesopredators (the brown rat, Rattus norvegicus, and kukri snake, Oligodon formosanus). Our results detail how fear of intraguild predation, conspecific cannibalism, habitat structure and territorial behaviour among these species interact in a complex fashion that results in high egg survival.

Effects of Human Disturbance on Terrestrial Apex Predators

The effects of human disturbance spread over virtually all ecosystems and ecological communities on Earth. In this review, we focus on the effects of human disturbance on terrestrial apex predators. We summarize their ecological role in nature and how they respond to different sources of human disturbance. Apex predators control their prey and smaller predators numerically and via behavioral changes to avoid predation risk, which in turn can affect lower trophic levels. Crucially, reducing population numbers and triggering behavioral responses are also the effects that human disturbance causes to apex predators, which may in turn influence their ecological role. Some populations continue to be at the brink of extinction, but others are partially recovering former ranges, via natural recolonization and through reintroductions. Carnivore recovery is both good news for conservation and a challenge for management, particularly when recovery occurs in human-dominated landscapes. Therefore, we conclude by discussing several management considerations that, adapted to local contexts, may favor the recovery of apex predator populations and their ecological functions in nature.

Behaviorally-mediated trophic cascade attenuated by prey use of risky places at safe times

The mere threat of predation may incite behavioral changes in prey that lead to community-wide impacts on productivity, biodiversity, and nutrient cycling. The paucity of experimental manipulations, however, has contributed to controversy over the strength of this pathway in wide-ranging vertebrate systems. We investigated whether simulated gray wolf (Canis lupus) presence can induce behaviorally-mediated trophic cascades, specifically, whether the 'fear' of wolf olfactory cues alone can change deer foraging behavior in ways that affect plants and soils. Wolves were recently removed from the Cedar Creek Ecosystem Science Reserve (Minnesota, USA), such that consumptively mediated predator effects were negligible. At 32 experimental plots, we crossed two nested treatments: wolf urine application and herbivore exclosures. We deployed camera traps to quantify how white-tailed deer (Odocoileus virginianus) adjusted their spatiotemporal habitat use, foraging, and vigilance in response to wolf cues and how these behavioral changes affected plant productivity, plant communities, and soil nutrients. Weekly applications of wolf urine significantly altered deer behavior, but deer responses did not cascade to affect plant or soil properties. Deer substantially reduced crepuscular activity at wolf-simulated sites compared to control locations. As wolves in this area predominantly hunted during mornings and evenings, this response potentially allows deer to maximize landscape use by accessing dangerous areas when temporal threat is low. Our experiment suggests that prey may be sensitive to 'dynamic' predation risk that is structured across both space and time and, consequentially, prey use of risky areas during safe times may attenuate behaviorally-mediated trophic cascades at the predator-prey interface.

Red deer allocate vigilance differently in response to spatio-temporal patterns of risk from human hunters and wolves

Abstract ContextUngulate prey can use increased vigilance to reduce their risk of predation, but little is known of the combined and interactive risk effects from humans and wolves in determining ungulate behaviour across time and space. Understanding the interplay between these risk effects is increasingly important, considering the recolonisation of several large carnivores to more human-dominated landscapes in Europe. AimThe aim of the present study was to assess the vigilance behaviour expressed by red deer (Cervus elaphus) in response to both humans and wolves in the Polish Białowieża Forest. MethodsUsing a camera-trap transect, the effect of distance to human settlements, hunting season, patterns of space use by wolves (Canis lupus), canopy openness, canopy height, time of day, as well as sex/age of individuals, on the vigilance behaviour observed in red deer was studied using a model-selection approach. Key resultsWe did not find a clear effect of patterns of space use by wolves or distance to human settlements on red deer vigilance behaviour at the landscape scale. However, red deer showed increased vigilance during the hunting season and during the day outside of protected areas and reserves, because disturbance from human hunters is highest. Conversely, we also found that red deer were more vigilant at night within more protected areas, which is likely to be explained by the increased activity of wolves because human activity is strictly limited. ConclusionsOur study showed that vigilance behaviour of red deer in Białowieża Primeval Forest is more driven by human hunting than by the frequency of wolf presence at a landscape scale. This could be explained by the higher temporal and spatial predictability of human hunting activities than wolf risk. We found that patterns of wolf space use, as opposed to the omnipresent fear effects from humans, had only localised effects by increasing vigilance levels during night hours in non-hunting areas of the forest. The reverse was observed outside of protected reserves. Understanding how prey species respond to this new combination of risk from natural predators and humans, is increasingly important in a landscape where human risk is becoming ever more potent and carnivores recolonise.

Predation risk increases intraspecific heterogeneity in white-tailed deer diel activity patterns

Prey species often mitigate predation risk through alteration of spatiotemporal diel activity patterns whereby prey access high-quality resources in risky areas during predator downtimes. However, dominance hierarchies exist in some prey species, and temporal partitioning is a mechanism thought to reduce aggressive intraspecific interactions. How demographic-specific responses to predation risk influence intraspecific temporal partitioning in prey are largely unknown and could be key to understanding the effects of predators on intraspecific interactions in prey. To assess the effects of predation risk on intraspecific interactions in white-tailed deer (Odocoileus virginianus), we monitored deer diel activity during the fawning season in four pairs of predator exclusion and control plots (~40 ha) from 2015 to 2018 using 16 camera traps. We examined the effect of predation risk on diel activity of males, females, and nursery groups by comparing the within-group coefficient of activity overlap (d̂) across predator exclusion and control plots. We then examined within-treatment activity overlap between groups in the predator exclosure and control plots. All groups maintained different diel activity patterns in safe and risky areas. Unconstrained by predation risk, all groups behaved more similarly, and interspecific group overlap was greater in the predator exclusion plots than control plots. Male-nursery group overlap exhibited the strongest treatment effect, increasing 24% in predator exclusion plots (d̂ = 0.91, confidence interval [CI]: 0.87–0.95) relative to control plots (d̂ = 0.67, CI: 0.57–0.76). Our results suggest predators increase heterogeneity in prey behavior and may be important drivers of behavioral processes, such as temporal partitioning, that minimize antagonistic intraspecific interactions of prey.

Outsized effect of predation: Wolves alter wetland creation and recolonization by killing ecosystem engineers

Gray wolves are a premier example of how predators can transform ecosystems through trophic cascades. However, whether wolves change ecosystems as drastically as previously suggested has been increasingly questioned. We demonstrate how wolves alter wetland creation and recolonization by killing dispersing beavers. Beavers are ecosystem engineers that generate most wetland creation throughout boreal ecosystems. By studying beaver pond creation and recolonization patterns coupled with wolf predation on beavers, we determined that 84% of newly created and recolonized beaver ponds remained occupied until the fall, whereas 0% of newly created and recolonized ponds remained active after a wolf killed the dispersing beaver that colonized that pond. By affecting where and when beavers engineer ecosystems, wolves alter all of the ecological processes (e.g., water storage, nutrient cycling, and forest succession) that occur due to beaver-created impoundments. Our study demonstrates how predators have an outsized effect on ecosystems when they kill ecosystem engineers.

Where and when to hunt? Decomposing predation success of an ambush carnivore

Predator-prey games emerge when predators and prey dynamically respond to the behavior of one another, driving the outcomes of predator-prey interactions. Predation success is a function of the combined probabilities of encountering and capturing prey, which are influenced by both prey behavior and environmental features. While the relative importance of encounter and capture probabilities have been evaluated in a spatial framework, temporal variation in prey behavior and intrinsic catchability are likely to also affect the distribution of predation events. Using a single-predator-single-prey (puma-vicuña) system, we evaluated which factors predict predation events across both temporal and spatial dimensions of the components of predation by testing the prey-abundance hypothesis (predators select for high encounter probability) and the prey-catchability hypothesis (predators select for high relative capture probability) in time and space. We found that for both temporal and spatial analyses, neither the prey-abundance hypothesis nor the prey-catchability hypothesis alone predicted kill frequency or distribution; puma kill frequency was static throughout the diel cycle and pumas consistently selected a single habitat type when hunting, despite temporal and spatial variation in encounter rates and intrinsic catchability. Our integrated spatiotemporal analysis revealed that an interaction between time of day and habitat influences kill probability, suggesting that trade-offs in the temporal and spatial components of predation drive the probability of predation events. These findings reinforce the importance of examining both the temporal and spatial patterns of the components of predation, rather than unidimensional measures of predator or prey behavior, to comprehensively describe the feedbacks between predator and prey in the predator-prey game.

Predation risk constrains herbivores' adaptive capacity to warming

Global warming compels larger endothermic animals to adapt either physiologically or behaviourally to avoid thermal stress, especially in tropical ecosystems. Their adaptive responses may however be compromised by other constraints, such as predation risk or starvation. Using an exceptional camera-trap dataset spanning 32 protected areas across southern Africa, we find that intermediate-sized herbivores (100-550 kg) switch activity to hotter times of the day when exposed to predation by lions. These herbivores face a tight window for foraging activity being exposed to nocturnal predation and to heat during the day, suggesting a trade-off between predation risk and thermoregulation mediated by body size. These findings stress the importance of incorporating trophic interactions into climate change predictions.

Fear the reaper: ungulate carcasses may generate an ephemeral landscape of fear for rodents

Animal carcasses provide an ephemeral pulse of nutrients for scavengers that use them. Carcass sites can increase species interactions and/or ephemeral, localized landscapes of fear for prey within the vicinity. Few studies have applied the landscape of fear to carcasses. Here, we use a mass die-off of reindeer caused by lightning in Norway to test whether rodents avoided larger scavengers (e.g. corvids and fox). We used the presence and abundance of faeces as a proxy for carcass use over the course of 2 years and found that rodents showed the strongest avoidance towards changes in raven abundance (β = -0.469, s.e. = 0.231, p-value = 0.0429), but not fox, presumably due to greater predation risk imposed by large droves of raven. Moreover, the emergence of rodent occurrence within the carcass area corresponded well with the disappearance of raven during the second year of the study. We suggest that carcasses have the potential to shape the landscape of fear for prey, but that the overall effects of carcasses on individual fitness and populations of species ultimately depend on the carcass regime, e.g. carcass size, count, and areal extent, frequency and the scavenger guild. We discuss conservation implications and how carcass provisioning and landscapes of fear could be potentially used to manage populations and ecosystems, but that there is a gap in understanding that must first be bridged.

A question of size and fear: competition and predation risk perception among frugivores and predators

Mammalian spatial and temporal activity patterns can vary depending on foraging behavior or the perception of predation or competition risk among species. These behaviors may in turn be altered by human influences such as defaunation. Herein, we evaluate whether frugivores avoid areas with high visitation rates by potential predators or competitors, and whether this avoidance changes in areas with different degrees of defaunation. We installed 189 cameras under fruit trees in six areas of the Atlantic Forest, Brazil, that differ in the abundance of top predators and large frugivores. Small predators and small frugivores were more frequent at night while large frugivores were more frequent during the day, but small frugivores visited and spent less time at fruiting trees on brighter nights, unlike large predators and large frugivores. Small frugivores also were less frequent in areas with high visitation by large frugivores and more frequent in highly defaunated areas. Our results suggest that the dynamics among mammalian functional groups varied according to diel patterns, potential competitors, and defaunation. We highlight the importance of understanding how species interactions are changing in areas exposed to strong human impacts to mitigate the indirect effects of defaunation.

Fear of the dark? A mesopredator mitigates large carnivore risk through nocturnality, but humans moderate the interaction

Abstract

While constrained by endogenous rhythms, morphology and ecology, animals may still exhibit flexible activity patterns in response to risk. Temporal avoidance of interspecific aggression can enable access to resources without spatial exclusion. Apex predators, including humans, can affect mesopredator activity patterns. Human context might also modify temporal interactions between predators. We explored activity patterns, nocturnality and the effects of human activity upon a guild of carnivores (grey wolf, Canis lupus; Eurasian lynx, Lynx lynx; red fox, Vulpes vulpes) using travel routes in Plitvice Lakes National Park, Croatia. Humans were diurnal, foxes nocturnal and large carnivores active during the night, immediately after sunrise and before sunset. Carnivore activity patterns overlapped greatly and to a similar extent for all pairings. Activity curves followed expectations based on interspecific killing, with activity peaks coinciding where body size differences were small (wolf and lynx) but not when they were intermediate (foxes to large carnivores). Carnivore activity, particularly fox, overlapped much less with that of diurnal humans. Foxes responded to higher large carnivore activity by being more nocturnal. Low light levels likely provide safer conditions by reducing the visual detectability of mesopredators. The nocturnal effect of large carnivores was however moderated and reduced by human activity. This could perhaps be due to temporal shielding or interference with risk cues. Subtle temporal avoidance and nocturnality may enable mesopredators to cope with interspecific aggression at shared spatial resources. Higher human activity moderated the effects of top-down temporal suppression which could consequently affect the trophic interactions of mesopredators.

Significance statement

Temporal partitioning can provide an important mechanism for spatial resource access and species coexistence. Our findings show that carnivores partition the use of shared travel routes in time, using the cover of darkness to travel safely where their suppressors (large carnivores) are more active. We however observed fox nocturnality to be flexible, with responses depending on the activity levels but also the composition of apex predators. High human activity modified the top-down temporal suppression of mesopredators by large carnivores. The use of time by predators can have demographic and trophic consequences. Prey accessibility and susceptibility can be temporally variable. As such, the ecosystem services and the ecological roles of predators may be affected by human time use as well as that of intraguild competitors. Temporal interactions should not be overlooked when evaluating human use and conservation priorities in protected areas.

Fear and stressing in predator-prey ecology: considering the twin stressors of predators and people on mammals

Predators induce stress in prey and can have beneficial effects in ecosystems, but can also have negative effects on biodiversity if they are overabundant or have been introduced. The growth of human populations is, at the same time, causing degradation of natural habitats and increasing interaction rates of humans with wildlife, such that conservation management routinely considers the effects of human disturbance as tantamount to or surpassing those of predators. The need to simultaneously manage both of these threats is particularly acute in urban areas that are, increasingly, being recognized as global hotspots of wildlife activity. Pressures from altered predator-prey interactions and human activity may each initiate fear responses in prey species above those that are triggered by natural stressors in ecosystems. If fear responses are experienced by prey at elevated levels, on top of responses to multiple environmental stressors, chronic stress impacts may occur. Despite common knowledge of the negative effects of stress, however, it is rare that stress management is considered in conservation, except in intensive ex situ situations such as in captive breeding facilities or zoos. We propose that mitigation of stress impacts on wildlife is crucial for preserving biodiversity, especially as the value of habitats within urban areas increases. As such, we highlight the need for future studies to consider fear and stress in predator-prey ecology to preserve both biodiversity and ecosystem functioning, especially in areas where human disturbance occurs. We suggest, in particular, that non-invasive in situ investigations of endocrinology and ethology be partnered in conservation planning with surveys of habitat resources to incorporate and reduce the effects of fear and stress on wildlife.

Territoriality drives preemptive habitat selection in recovering wolves: Implications for carnivore conservation

According to the ideal-free distribution (IFD), individuals within a population are free to select habitats that maximize their chances of success. Assuming knowledge of habitat quality, the IFD predicts that average fitness will be approximately equal among individuals and between habitats, while density varies, implying that habitat selection will be density dependent. Populations are often assumed to follow an IFD, although this assumption is rarely tested with empirical data, and may be incorrect when territoriality indicates habitat selection tactics that deviate from the IFD (e.g. ideal-despotic distribution or ideal-preemptive distribution). When territoriality influences habitat selection, species' density will not directly reflect components of fitness such as reproductive success or survival. In such cases, assuming an IFD can lead to false conclusions about habitat quality. We tested theoretical models of density-dependent habitat selection on a species known to exhibit territorial behaviour in order to determine whether commonly applied habitat models are appropriate under these circumstances. We combined long-term radiotelemetry and census data from grey wolves Canis lupus in the Upper Peninsula of Michigan, USA to relate spatiotemporal variability in wolf density to underlying classifications of habitat within a hierarchical state-space modelling framework. We then iteratively applied isodar analysis to evaluate which distribution of habitat selection best described this recolonizing wolf population. The wolf population in our study expanded by >1,000% during our study (~50 to >600 individuals), and density-dependent habitat selection was most consistent with the ideal-preemptive distribution, as opposed to the ideal-free or ideal-despotic alternatives. Population density of terrestrial carnivores may not be positively correlated with the fitness value of their habitats, and density-dependent habitat selection patterns may help to explain complex predator-prey dynamics and cascading indirect effects. Source-sink population dynamics appear likely when species exhibit rapid growth and occupy interspersed habitats of contrasting quality. These conditions are likely and have implications for large carnivores in many systems, such as areas in North America and Europe where large predator species are currently recolonizing their former ranges.

Optimisation of energetic and reproductive gains explains behavioural responses to environmental variation across seasons and years

Animals switch between inactive and active states, simultaneously impacting their energy intake, energy expenditure and predation risk, and collectively defining how they engage with environmental variation and trophic interactions. We assess daily activity responses to long-term variation in temperature, resources and mating opportunities to examine whether individuals choose to be active or inactive according to an optimisation of the relative energetic and reproductive gains each state offers. We show that this simplified behavioural decision approach predicts most activity variation (R²  = 0.83) expressed by free-ranging red squirrels over 4 years, as quantified through accelerometer recordings (489 deployments; 5066 squirrel-days). Recognising activity as a determinant of energetic status, the predictability of activity variation aggregated at a daily scale, and the clear signal that behaviour is environmentally forced through optimisation of gain, provides an integrated approach to examine behavioural variation as an intermediary between environmental variation and energetic, life-history and ecological outcomes.