Putting predators back into behavioral predator–prey interactions

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.

Invasive mammalian predators habituate to and generalize avian prey cues: a mechanism for conserving native prey

Invasive mammalian predators can cause the decline and extinction of vulnerable native species. Many invasive mammalian predators are dietary generalists that hunt a variety of prey. These predators often rely upon olfaction when foraging, particularly at night. Little is understood about how prey odor cues are used to inform foraging decisions. Prey cues can vary spatially and temporally in their association with prey and can either reveal the location of prey or lead to unsuccessful foraging. Here we examine how two wild-caught invasive mammalian bird predator species (European hedgehogs Erinaceus europaeus and ferrets Mustela putorius furo) respond to unrewarded bird odors over successive exposures, first demonstrating that the odors are perceptually different using house mice (Mus musculus) as a biological olfactometer. We aim to test if introduced predators categorize odor cues of similar prey together, a tactic that could increase foraging efficiency. We exposed house mice to the odors using a standard habituation/dishabituation test in a laboratory setting, and wild-caught European hedgehogs and ferrets in an outdoor enclosure using a similar procedure. Mice discriminated among all bird odors presented, showing more interest in chicken odor than quail or gull odor. Both predator species showed a decline in interest toward unrewarded prey odor (i.e., habituation), but only ferrets generalized their response from one unrewarded bird odor to another bird odor. Hedgehog responses to unrewarded bird odors were highly variable between individuals. Taken together, our results reveal interspecific and intraspecific differences in response to prey odors, which we argue are a consequence of different diet breadth, life and evolutionary histories, and the conditions in each experiment. Generalization of prey odors may have enabled some species of invasive predators to efficiently hunt a range of intraguild prey species, for example, ground-nesting shorebirds. Olfactory manipulation of predators may be a useful conservation tool for threatened prey if it reduces the conspicuousness of vulnerable prey.

Do Carolina chickadees (Poecile carolinensis) and tufted titmice (Baeolophus bicolor) use predator eyes in risk assessment?

Previous studies have found that Carolina chickadees and tufted titmice use a predator's head orientation to determine risk, taking fewer seeds from a feeder if an avian predator model's head is facing the feeder while ignoring the head orientation. In addition to head orientation, eyes are a cue of predator risk. In the current study, I examined whether or not chickadees and titmice used the presence of eyes of a predator model to determine when to forage for food. Plastic owl models, with their eyes covered or uncovered, were presented to wild flocks of chickadees and titmice. To test whether or not chickadees and titmice would respond to the presence of eyes, the number of seeds taken and the calling behavior of birds were compared between the two types of predator presentations (eyes covered or uncovered). Chickadees and titmice took fewer seeds when the eyes were uncovered than when they were covered. Chickadees also gave significantly more introductory notes, often used in association with the presence of predators or risk, in their calls when the eyes were visible than when the eyes of the predator model were covered. The results indicate that chickadees and titmice can use the presence of eyes on predators to determine predation risk and possibly use eye gaze to determine where a predator is looking.

Aquatic beetles influence colonization of disparate taxa in small lentic systems

Structure of natural communities is shaped by both abiotic characteristics and the ongoing processes of community assembly. Important to this process are the habitat selection behaviors and subsequent survival of colonists, both in the context of temporal changes in the abiotic characteristics and priority effects driven by earlier colonists. Aquatic beetles are prevalent in temporary freshwater systems, form speciose assemblages, and are often early colonists of temporary ponds. While beetles have the potential to influence community structure through post-colonization interactions (predation and competition), our goal was to determine whether the presence of beetle assemblages (versus patches without beetles) influences the colonization and oviposition of a diverse group of animals in a naturally colonized experimental landscape. We established mesocosms that either contained existing beetle assemblages or contained no beetles and assessed abundances of subsequent colonists. Treefrogs, Hyla chrysoscelis, and mosquitoes, Culex restuans, both deposited fewer eggs in patches containing beetle assemblages, while two beetles, Copelatus glyphicus and Paracymus, colonized those patches at lower rates. One beetle, Helophorus linearis, colonized patches containing beetle assemblages at higher rates, while two beetles, Berosus infuscatus and Tropisternus lateralis, exhibited no colonization differences between treatments. Overall, there were no differences in the assemblage structure or richness of beetles that colonized patches. Our results illustrate the importance of species-specific habitat selection behavior in determining the species composition of habitat patches, while emphasizing the role of priority effects in influencing patterns of community assembly. Habitat selection in response to abiotic and biotic characteristics of habitat patches can potentially create greater spatiotemporal niche separation among the numerous, often closely related species (phylogenetically and trophically), that can be simultaneously found in similar patches across landscapes.

Circadian activity patterns of mammalian predators and prey in Costa Rica

Temporal niche shifts can shape predator-prey interactions by enabling predator avoidance, enhancing feeding success, and reducing competition among predators. Using a community-based conservation approach, we investigated temporal niche partitioning of mammalian predators and prey across 12 long-term camera trap surveys in the Pacific slope and Talamanca Cordillera of Costa Rica. Temporal overlap and segregation were investigated between predator-prey and predator-predator pairs using overlap analysis, circular statistics, and relative abundance after accounting for differences in habitat, season, and human impact among sites. We made the assumption that predators select abundant prey and adjust their activity to maximize their temporal overlap, thus we predicted that abundant prey with high overlap would be preferred prey species for that predator. We also predicted that similar-sized pairs of predator species with the greatest potential for competitive interactions would have the highest temporal segregation. Our results supported the existence of temporal niche separation among the eight species of predators-the smaller Leopardus felids (ocelot, margay, oncilla) were primarily nocturnal, the largest felids (jaguar and puma) and coyote were cathemeral, and the smaller jaguarundi and tayra were mostly diurnal. Most prey species (67%) were primarily nocturnal versus diurnal or cathemeral (33%). Hierarchical clustering identified relationships among species with the most similar activity patterns. We discuss the primary prey and competitor species predicted for each of the eight predators. Contrary to our prediction, the activity pattern of similar-sized intraguild competitors overlapped more than dissimilar-sized competitors, suggesting that similar-sized predators are hunting the same prey at the same time. From this we conclude that prey availability is more important than competition in determining circadian activity patterns of Neotropical predators. Our results indicate the presence of a delicate balance of tropical food webs that may be disrupted by overhunting, leading to a depauperate community consisting of ubiquitous generalists and endangered specialists. With Central America a hotspot for hunting-induced "empty forests," community-based conservation approaches may offer the best road to reduce illegal hunting and maintain the biodiversity and community structure of tropical forest systems.

Mate-searching context of prey influences the predator-prey space race

Predation risk is a strong driver of prey distribution and movement. However, fitness-influencing behaviours, such as mating, can alter risk and influence predator-prey space-use dynamics. In tree crickets, Oecanthus henryi, mate searching involves acoustic signalling by immobile males and phonotactic movement by females. Space-use patterns in tree crickets relative to their primary predators, green lynx spiders (Peucetia viridans), should therefore depend on their current mate-searching state; whether males are calling or non-calling and whether females are phonotactic or non-phonotactic. We first measured the degree of spatial anchoring of crickets to specific bushes in the field and determined whether that influenced the probability of broad-scale spatial overlap with spiders. In the absence of spiders, all crickets, independent of sex or male calling status, were found to be spatially anchored to specific types of bushes and not uniformly distributed on the landscape. At the broad spatial scale, spiders were more likely to be found on bushes with female crickets and, to a lesser degree, calling male crickets. At a finer spatial scale within a bush, movement strategies of crickets not only varied depending on the presence or absence of a spider, but also on their current mate-searching state. Phonotactic females showed clear predator avoidance, whereas calling and non-calling males moved towards the spider instead of away, similar to predator inspection behaviour seen in many taxa. As the strongly selected sex, males are more likely to undertake risky mate-searching activities, which includes inspection of predator positions. Overall, we found that all crickets were predictably anchored at the landscape scale, but their sex and mate-seeking behaviour influenced the degree of overlap with predators and their antipredator movement strategies. Reproductive strategies within a prey species, therefore, can alter predator-prey space race at multiple spatial scales.

Running performance with emphasis on low temperatures in a Patagonian lizard, Liolaemus lineomaculatus

Lizard activity and endurance of cold climate is regulated by several factors such as evolutionary potential, acclimatization capacity, physiological tolerance, and locomotion among thermally advantageous microenvironments. Liolaemus lineomaculatus, a lizard inhabiting a wide range of cold environments in Patagonia, provides an excellent model to test interpopulation variability in thermal performance curves (TPCs) and usage of microhabitats. We obtained critical thermal minima and maxima, and performed running trials at eight temperatures using lizards from both a temperate-site (high-altitude) population at 42° S and a cold-site population at 50° S. The availability of environmental temperatures for running performance in open ground and in potential lizard refuges were recorded, and showed that lizards in the temperate site had a greater availability of thermal environments offering temperatures conducive to locomotion. Generalized additive mixed models showed that the two populations displayed TPCs of different shapes in 0.15 m runs at temperatures near their optimal temperature, indicating a difference in thermal sensitivity at high temperatures. However, the rest of the locomotor parameters remained similar between Liolaemus lineomaculatus from thermal and ecological extremes of their geographic distribution and this may partly explain their ability to endure a cold climate.

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.

An ecological framework for contextualizing carnivore-livestock conflict

Carnivore predation on livestock is a complex management and policy challenge, yet it is also intrinsically an ecological interaction between predators and prey. Human-wildlife interactions occur in socioecological systems in which human and environmental processes are closely linked. However, underlying human-wildlife conflict and key to unpacking its complexity are concrete and identifiable ecological mechanisms that lead to predation events. To better understand how ecological theory accords with interactions between wild predators and domestic prey, we developed a framework to describe ecological drivers of predation on livestock. We based this framework on foundational ecological theory and current research on interactions between predators and domestic prey. We used this framework to examine ecological mechanisms (e.g., density-mediated effects, behaviorally mediated effects, and optimal foraging theory) through which specific management interventions operate, and we analyzed the ecological determinants of failure and success of management interventions in 3 case studies: snow leopards (Panthera uncia), wolves (Canis lupus), and cougars (Puma concolor). The varied, context-dependent successes and failures of the management interventions in these case studies demonstrated the utility of using an ecological framework to ground research and management of carnivore-livestock conflict. Mitigation of human-wildlife conflict appears to require an understanding of how fundamental ecological theories work within domestic predator-prey systems.

Rethinking trophic niches: Speed and body mass colimit prey space of mammalian predators

Realized trophic niches of predators are often characterized along a one-dimensional range in predator-prey body mass ratios. This prey range is constrained by an "energy limit" and a "subdue limit" toward small and large prey, respectively. Besides these body mass ratios, maximum speed is an additional key component in most predator-prey interactions.Here, we extend the concept of a one-dimensional prey range to a two-dimensional prey space by incorporating a hump-shaped speed-body mass relation. This new "speed limit" additionally constrains trophic niches of predators toward fast prey.To test this concept of two-dimensional prey spaces for different hunting strategies (pursuit, group, and ambush predation), we synthesized data on 63 terrestrial mammalian predator-prey interactions, their body masses, and maximum speeds.We found that pursuit predators hunt smaller and slower prey, whereas group hunters focus on larger but mostly slower prey and ambushers are more flexible. Group hunters and ambushers have evolved different strategies to occupy a similar trophic niche that avoids competition with pursuit predators. Moreover, our concept suggests energetic optima of these hunting strategies along a body mass axis and thereby provides mechanistic explanations for why there are no small group hunters (referred to as "micro-lions") or mega-carnivores (referred to as "mega-cheetahs").Our results demonstrate that advancing the concept of prey ranges to prey spaces by adding the new dimension of speed will foster a new and mechanistic understanding of predator trophic niches and improve our predictions of predator-prey interactions, food web structure, and ecosystem functions.

Fire's impact on threat detection and risk perception among vervet monkeys: Implications for hominin evolution

The spatial behavior of primates is shaped by many factors including predation risk, the distribution of food sources, and access to water. In fire-prone settings, burning is a catalyst of change, altering the distribution of both plants and animals. Recent research has shown that primates alter their behavior in response to this change. Here, we study primates' perceived threat of predation in fire-modified landscapes. We focus on the predator-related behaviors of vervet monkeys (Chlorocebus pygerythrus) after controlled burning events. We compare the occurrence of vigilance and predator-deterrent behaviors, including alarm calls, scanning, and flight across different habitats and burn conditions to test the hypothesis that subjects exhibit fewer predator-specific vigilance and predator-deterrent behaviors in burned areas. The results demonstrate that predator-related behaviors occur less often in burned habitats, suggesting that predators are less common in these areas. These results provide foundations for examining hypotheses about the use of fire-altered landscapes among extinct hominins. We set these data in the context of increasing aridity, changes in burning regimes, and the emergence of pyrophilia in the human lineage.

Zooming in on mechanistic predator-prey ecology: Integrating camera traps with experimental methods to reveal the drivers of ecological interactions

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.

Adaptations of the red fox (Vulpes vulpes) to urban environments in Sydney, Australia

With urban encroachment on wild landscapes accelerating globally, there is an urgent need to understand how wildlife is adapting to anthropogenic change. We compared the behaviour of the invasive red fox (Vulpes vulpes) at eight urban and eight peri-urban areas of Sydney, Australia. We observed fox behaviour around a lure and compared fox activity patterns to those of potential prey and to two domestic predators (dogs—Canis lupus familiaris and cats—Felis catus). We assessed the influence of site type, vegetation cover, and distance from habitation on fox behaviour, and compared the temporal activity patterns of urban and peri-urban red foxes. Urban red foxes were marginally more nocturnal than those in peri-urban areas (88% activity overlap). There was greater overlap of red fox activity patterns with introduced mammalian prey in urban areas compared with peri-urban areas (90% urban vs 84% peri-urban). Red fox temporal activity overlapped 78% with cats, but only 20% with dogs, across both site types. The high degree of overlap with cats and introduced mammalian prey is most likely explained by the nocturnal behaviour of these species, while pet dogs are generally kept in yards or indoors at night. The behavioural differences we documented by urban red foxes suggest they may adapt to human modifications and presence, by being more nocturnal and/or more confident in urban areas.

Phytoseiid predatory mites can disperse entomopathogenic fungi to prey patches

Recent studies have shown that predatory mites used as biocontrol agents can be loaded with entomopathogenic fungal conidia to increase infection rates in pest populations. Under laboratory conditions, we determined the capacity of two phytoseiid mites, Amblyseius swirskii and Neoseiulus cucumeris to deliver the entomopathogenic fungus Beauveria bassiana to their prey, Frankliniella occidentalis. Predatory mites were loaded with conidia and released on plants that had been previously infested with first instar prey clustered on a bean leaf. We examined each plant section to characterize the spatial distribution of each interacting organism. Our results showed that A. swirskii delivered high numbers of conidia to thrips infested leaves, thereby increasing the proportion of thrips that came into contact with the fungus. The effect was larger when thrips infestation occurred on young leaves than on old leaves. Neoseiulus cucumeris delivered less conidia to the thrips infested leaves. These patterns result from differences in foraging activity between predatory mite species. Amblyseius swirskii stayed longer on plants, especially within thrips colonies, and had a stronger suppressing effect on thrips than N. cucumeris. Our study suggests that loading certain predatory mite species with fungal conidia can increase their capacity to suppress thrips populations by combining predation and dispersing pathogens.

Adaptive migration promotes food web persistence

Interactions between diverse species that coexist in nature are of utmost interest in the field of ecology. Recent theoretical studies have shown that spatiality plays a key role in maintaining complex systems with multiple differing species. In these models, however, organisms move among habitats randomly, implying that some organisms migrate from areas of higher fitness to areas of lower fitness in a maladaptive way. Herein, a meta-community model of a food web shows that adaptive movements by organisms can play key roles in maintaining large ecological communities. Without adaptive dispersal, species are not likely to persist across habitats, particularly when systems have few habitats where local food webs are strongly coupled by high migration rates. However, adaptive dispersers can improve such low persistence greatly. By abandoning unfavourable habitats for favourable habitats, dispersers prevent regional extinction at the price of local extinction and increase their total numbers further. Hence, the inherent stabilising effect of spatiality may be larger than that expected from theoretical random movement models.

Individual willingness to leave a safe refuge and the trade-off between food and safety: a test with social fish

Refuges offer prey animals protection from predation, but increased time spent hiding can reduce foraging opportunities. Within social groups, individuals vary in their refuge use and willingness to forage in the presence of a predator. Here, we examine the relative foraging benefits and mortality costs associated with individual refuge use and foraging behaviour within groups of goldfish (Carassius auratus) under predation risk from an avian predator (little egret-Egretta garzetta). We assessed individual order of emergence from the refuge and participation over 15 group foraging outings, and assigned each fish a daily outing index score. The individual fish that emerged from the refuge earlier than the other group members and that participated in more outings received high outing index scores and consumed more food compared with fish that tended to emerge in posterior positions and participate in fewer outings. However, individual fish that attained high outing index scores suffered a higher risk of predation. Furthermore, the amount of time the egret spent at the pool affected group foraging behaviour: as predation risk increased, groups of fish consumed significantly less food. Our results exemplify the trade-off between foraging success and safety from predation that prey species regularly experience.

Are all patches worth exploring? Foraging desert birds do not rely on environmental indicators of seed abundance at small scales

Background

Consumers should show strong spatial preferences when foraging in environments where food availability is highly heterogeneous and predictable. Postdispersal granivores face this scenario in most arid areas, where soil seed bank abundance and composition associates persistently with vegetation structure at small scales (decimetres to metres). Those environmental features should be exploited as useful pre-harvest information, at least to avoid patches predicted to be poor. However, we did not find the expected spatial association in the algarrobal of the central Monte desert by observing foraging seed-eating birds, a field technique influenced by how much they exploit visited patches. In this work we tested if the first stage of foraging by granivorous birds (patch visit, encounter or exploration) is positively associated with environmental indicators of patch quality by recording the removal of single seeds from 300 scattered experimental devices during seasonal trials. Spatial selectivity was analysed by comparing the structural characteristics of used vs. available microhabitats, and evaluated against bottom-up and top-down hypotheses based on our previous knowledge on local seed bank abundance, composition and dynamics. Their foraging activity was also explored for spatial autocorrelation and environmental correlates at bigger scales.

Results

Postdispersal granivorous birds were less selective in their use of foraging space than expected if microhabitat appearance were providing them relevant information to guide their search for profitable foraging patches. No microhabitat type, as defined by their vegetation structure and soil cover, remained safe from bird exploration. Analyses at bigger temporal and spatial scales proved more important to describe heterogeneity in seed removal.

Conclusions

Closeness to tall trees, probably related to bird territoriality and reproduction or to their perception of predation risk, seemed to determine a first level of habitat selection, constraining explorable space. Then, microhabitat openness (rather than seed abundance) exerted some positive influence on which patches were more frequently visited among those accessible. Selective patterns by birds at small scales were closer to our predictions of a top-down spatial effect, with seed consumption creating or strengthening (and not responding to) the spatial pattern and dynamics of the seed bank.

Electronic supplementary material

The online version of this article (10.1186/s12898-019-0242-z) contains supplementary material, which is available to authorized users.

Time to revisit? A predator's previous successes and failures in prey capture determine its return time to patches

In a heterogeneous environment containing multiple patches that may deplete and renew, a forager should be able to detect the quality of food resources within and among patches and choose to exploit them to best maximize returns. From the predator's perspective, the behavioral responses of the prey in a patch will be perceived as depletion when they retreat to refuge and renewal when they reemerge. A predator encountering responsive prey should manage predation risk, and thus behavioral resource depression, by optimally timing its return time to the patch based on prey behavior. We evaluated the foraging decisions of a predator that encountered patches differing in size of the refuge and prey density. We used little egrets and goldfish as predators and prey in an environment that contained three patches (pools). We manipulated prey density and refuge size and availability (using covers) and observed predator foraging behavior. When the egret had previously caught a fish it did not discriminate between the pools, and the return time was similar for all cover types. The fish densities also did not affect the egret decisions to return to pools. However, when it failed to catch fish, it returned sooner to the pool containing the small cover than the larger one. Additionally, after failing to catch fish in patches containing the highest prey density, the egrets subsequently preferred to return to such patches sooner. We show experimentally that previous failures influence the foraging decisions of a predator choosing how quickly to return to a previously visited patch.

Fine-scale behavioural adjustments of prey on a continuum of risk

In the wild, prey species often live in the vicinity of predators, rendering the ability to assess risk on a moment-to-moment basis crucial to survival. Visual cues are important as they allow prey to assess predator species, size, proximity and behaviour. However, few studies have explicitly examined prey's ability to assess risk based on predator behaviour and orientation. Using mosquitofish, Gambusia holbrooki, and their predator, jade perch, Scortum barcoo, under controlled conditions, we provide some of the first fine-scale characterization of how prey adapt their behaviour according to their continuous assessment of risk based on both predator behaviour and angular distance to the predator's mouth. When these predators were inactive and posed less of an immediate threat, prey within the attack cone of the predator showed reductions in speed and acceleration characteristic of predator-inspection behaviour. However, when predators became active, prey swam faster with greater acceleration and were closer together within the attack cone of predators. Most importantly, this study provides evidence that prey do not adopt a uniform response to the presence of a predator. Instead, we demonstrate that prey are capable of rapidly and dynamically updating their assessment of risk and showing fine-scale adjustments to their behaviour.

An experimental test of how parasites of predators can influence trophic cascades and ecosystem functioning

Parasites can shape the structure and function of ecosystems by influencing both the density and traits of their hosts. Such changes in ecosystems are particularly likely when the host is a predator that mediates the dynamics of trophic cascades. Here, we experimentally tested how parasite load of a small predatory fish, the threespine stickleback, can affect the occurrence and strength of trophic cascades and ecosystem functioning. In a factorial mesocosm experiment, we manipulated the density of stickleback (low vs. high), and the level of parasite load (natural vs. reduced). In addition, we used two stickleback populations from different lineages: an eastern European lineage with a more pelagic phenotype (Lake Constance) and a western European lineage with a more benthic phenotype (Lake Geneva). We found that stickleback caused trophic cascades in the pelagic but not the benthic food chain. Evidence for pelagic trophic cascades was stronger in treatments where parasite load of stickleback was reduced with an antihelmintic medication, and where fish originated from Lake Constance (i.e., the more pelagic lineage). A structural equation model revealed that differences in stickleback lineage and parasite load were most likely to impact trophic cascades via changes in the composition, rather than overall biomass, of zooplankton communities. Overall, our results provide experimental evidence that parasites of predators can influence the cascading effects of fish on lower trophic levels with consequences on ecosystem functioning.

Predation risk and space use of a declining Dall sheep (Ovis dalli dalli) population

The abundance of ungulate populations may fluctuate in response to several limiting factors, including climate, diseases, and predation. In the northern Richardson Mountains, Canada, Dall sheep (Ovis dalli dalli) have undergone a major decline in the past decades and predation by grizzly bears (Ursus arctos) and wolves (Canis lupus) was suspected as a leading cause. To better understand the relationship between these three species located in this rugged and remote ecosystem, we relied on a combination of indirect methods. We investigated the apparent role of predation on the Dall sheep population using spatial ecology and stable isotopes. We examined seasonal variation in predation risk, focusing on how it may affect Dall sheep habitat use and sexual segregation, and we evaluated the proportion of Dall sheep in the diet of both predators using stable isotopes. The movements of the three species were monitored by satellite telemetry. Dall sheep habitat use patterns were analyzed using topographical features, greenness index, land cover, and apparent predation risk. The diets of grizzly bears and wolves were examined using a Bayesian mixing model for carbon and nitrogen stable isotopes. We found that Dall sheep habitat use varied seasonally, with different patterns for ewes and rams. Exposure to grizzly bear risk was higher for rams during summer, while ewes were further exposed to wolf apparent predation risk during winter. The importance of safe habitats for ewes was reflected in space use patterns. Stable isotopes analyses suggested that the diet of grizzly bears was largely from animal sources, with mountain mammals comprising about one quarter. Wolves mostly fed on both aquatic browsers and mountain mammals. Diet variation between individual predators suggested that some individuals specialized on mountain mammals, likely including Dall sheep. We conclude that grizzly bear and wolf apparent predation risk are important in driving Dall sheep habitat use and play a role in sexual segregation. Overall, this study presents an innovative combination of indirect methods that could be applied elsewhere to better understand predator-prey dynamics in remote ecosystems.

Landscapes of Fear: Spatial Patterns of Risk Perception and Response

Animals experience varying levels of predation risk as they navigate heterogeneous landscapes, and behavioral responses to perceived risk can structure ecosystems. The concept of the landscape of fear has recently become central to describing this spatial variation in risk, perception, and response. We present a framework linking the landscape of fear, defined as spatial variation in prey perception of risk, to the underlying physical landscape and predation risk, and to resulting patterns of prey distribution and antipredator behavior. By disambiguating the mechanisms through which prey perceive risk and incorporate fear into decision making, we can better quantify the nonlinear relationship between risk and response and evaluate the relative importance of the landscape of fear across taxa and ecosystems.

Hybrid approach to modeling spatial dynamics of systems with generalist predators

We consider hybrid spatial modeling approaches for ecological systems with a generalist predator utilizing a prey and either a second prey or an allochthonous resource. While spatial dispersion of populations is often modeled via stepping-stone (discrete spatial patches) or continuum (one connected spatial domain) formulations, we shall be interested in hybrid approaches which we use to reduce the dimension of certain components of the spatial domain, obtaining either a continuum model of varying spatial dimensions, or a mixed stepping-stone-continuum model. This approach results in models consisting of partial differential equations for some of the species which are coupled via reactive boundary conditions to lower dimensional partial differential equations or ordinary differential equations for the other species. In order to demonstrate the use of this approach, we consider two case studies. In the first case study, we consider a one-predator two-prey interaction between beavers, wolves and white-tailed deer in Voyageurs National Park. In the second case study, we consider predator-prey-allochthonous resource interactions between bears, berries and salmon on Kodiak Island. For each case study, we compare the results from the hybrid modeling approach with corresponding stepping-stone and continuum model results, highlighting benefits and limitations of the method. In some cases, we find that the hybrid modeling approach allows for solutions which are easier to simulate (akin to stepping-stone models) while maintaining seemingly more realistic spatial dynamics (akin to full continuum models).

Coordinated hunting behaviors of mixed-species groups of piscivores and associated species at Isla del Coco National Park (Eastern Tropical Pacific)

ABSTRACT Studies of mixed-species groups of animals can reveal emergent complexities of collective behaviors. In this study we collected data on mixed-species hunting groups composed primarily of piscivorous fishes (species composition, abundance, behavioral interactions) and used both multivariate and network analyses to quantify pair-wise and guild level behavioral relationships. Our results indicate that such collective behaviors exhibit consistent patterns of associations (33 species with 282 pair-wise links within the observed network) with 10 dominant species accounting for 60% of pair-wise interactions. Species richness within groups varied (mean = 2.4, range 2-6 species) as did group size (mean = 8.1 individuals, range 2-80). Mixed-species groups, in general, were composed of species representing morphologically diverse forms that appeared to enhance access to shelter sites and implement diverse strategies for prey capture. It is noteworthy that the composition of groups did not reflect the relative abundances of their component species within the overall community of fishes, suggesting that group membership was an elective choice. The identification of these patterns, assuming they are persistent features of these communities, can be used as a foundation for studies to assess dynamics of mixed-species relationships, rates of predator success based on group membership, demographic consequences, and responses to variations in habitat attributes and associated prey resources. Such information could be used to interpret the nature of multispecies interactions within predator communities and potentially aid in conservation and management.