Harvesting creates ecological traps: consequences of invisible mortality risks in predator-prey metacommunities

Models of two-patch predator-prey metacommunities are used to explore how the global predator population changes in response to additional mortality in one of the patches. This could describe the dynamics of a predator in an environment that includes a refuge area where that predator is protected and a spatially distinct ("risky") area where it is harvested. The predator's movement is based on its perceived fitness in the two patches, but the risk from the additional mortality is potentially undetectable; this often occurs when the mortality is from human harvesting or from a novel type of top predator. Increases in undetected mortality in the risky area can produce an abrupt collapse of either the refuge population or of the entire predator population when the mortality rate exceeds a threshold level. This is due to the attraction of the risky patch, which has abundant prey due to its high predator mortality. Extinction of the refuge predator population does not occur when the refuge patch has a higher maximum per capita predator growth rate than the exploited patch because the refuge is then more attractive when the predator is rare. The possibility of abrupt extinction of one or both patches from high densities in response to a small increase in harvest is often associated with alternative states. In such cases, large reductions in mortality may be needed to avoid extinction in a collapsing predator population, or to reestablish an extinct population. Our analysis provides a potential explanation for sudden collapses of harvested populations, and it argues for more consideration of adaptive movement in designing protected areas.     

Response of predators to loss and fragmentation of prey habitat: a review of theory

Despite extensive empirical research and previous reviews, no clear patterns regarding the effects of habitat loss and fragmentation on predator-prey interactions have emerged. We suggest that this is because empirical researchers do not design their studies to test specific hypotheses arising from the theoretical literature. In fact, theoretical work is almost completely ignored by empirical researchers, perhaps because it may be inaccessible to them. The purpose of this paper is to review theoretical work on the effects of habitat loss and fragmentation on predator-prey interactions. We provide a summary of clear, testable theoretical predictions for empirical researchers. To test one or more of these predictions, an empiricist will need certain information on the predator and prey species of interest. This includes: (1) whether the predator is a specialist on one prey species or feeds on many kinds of prey (omnivore and generalist); (2) whether the predator is restricted to the same habitat type as the focal prey (specialist), can use a variety of habitats but has higher survival in the prey habitat (omnivore), or lives primarily outside of the focal prey's habitat (generalist); (3) whether prey-only patches have lower prey extinction rates than predator-prey patches; and (4) whether the prey emigrate at higher rates from predator-prey patches than from prey-only patches. Empiricists also need to be clear on whether they are testing a prediction about habitat loss or habitat fragmentation and need to conduct empirical studies at spatial scales appropriate for testing the theoretical prediction(s). We suggest that appropriate use of the theoretical predictions in future empirical research will resolve the apparent inconsistencies in the empirical literature on this topic.     

Can rare positive interactions become common when large carnivores consume livestock?

Livestock populations in protected areas are viewed negatively because of their interaction with native ungulates through direct competition for food resources. However, livestock and native prey can also interact indirectly through their shared predator. Indirect interactions between two prey species occur when one prey modifies either the functional or numerical responses of a shared predator. This interaction is often manifested as negative effects (apparent competition) on one or both prey species through increased predation risk. But indirect interactions can also yield positive effects on a focal prey if the shared predator modifies its functional response toward increased consumption of an abundant and higher-quality alternative prey. Such a phenomenon between two prey species is underappreciated and overlooked in nature. Positive indirect effects can be expected to occur in livestock-dominated wildlife reserves containing large carnivores. We searched for such positive effects in Acacia-Zizhypus forests of India's Gir sanctuary where livestock (Bubalus bubalis and Bos indicus) and a coexisting native prey (chital deer, Axis axis) are consumed by Asiatic lions (Panthera leo persica). Chital vigilance was higher in areas with low livestock density than in areas with high livestock density. This positive indirect effect occurred because lion predation rates on livestock were twice as great where livestock were abundant than where livestock density was low. Positive indirect interactions mediated by shared predators may be more common than generally thought with rather major consequences for ecological understanding and conservation. We encourage further studies to understand outcomes of indirect interactions on long-term predator-prey dynamics in livestock-dominated protected areas.     

The influence of size-specific indirect interactions in predator-prey systems

Nonlethal indirect interactions between predators often lead to nonadditive effects of predator number on prey survival and growth. Previous studies have focused on systems with at least two different predator species and one prey species. However, most predators undergo extreme ontological changes in phenotype such that interactions between different-sized cohorts of a predator and its prey could lead to nonadditive effects in systems with only two species. This may be important since different-sized individuals of the same species can differ more in their ecology than similar-sized individuals of different species. This study examined trait-mediated indirect effects in a two-species system including a cannibalistic predator with different-sized cohorts and its prey. I tested for these effects using larvae of two stream salamanders, Gyrinophilus porphyriticus (predator) and Eurycea cirrigera (prey), by altering the densities and combinations of predator size classes in experimental streams. Results showed that the presence of large individuals can significantly reduce the impact of density changes of smaller conspecifics on prey survival through nonlethal means. In the absence of large conspecifics, an increase in the relative frequency of small predators significantly increased predation rates, thereby reducing prey survival. However, with large conspecifics present, increasing the density of small predators did not decrease prey survival, resulting in a 14.3% lower prey mortality than predicted from the independent effects of both predator size classes. Small predators changed their microhabitat use in the presence of larger conspecifics. Prey individuals reduced activity in response to large predators but did not respond to small predators. Both predators reduced prey growth. These results demonstrate that the impact of a predator can be significantly altered by two different types of trait-mediated indirect effects in two-species systems: between different-sized cohorts and between different cohorts and prey. This study demonstrates that predictions based on simple numerical changes that assume independent effects of different size classes or ignore size structure can be strongly misleading. We need to account for the size structure within predator populations in order to predict how changes in predator abundance will affect predator-prey dynamics.     

Predators choosing between patches with standing crop: the influence of switching rules and input types

Where prey arriving in a patch are not consumed immediately, they will accumulate. Predators are then presented with a prey density or standing crop that increases through further input, and decreases through the consumption by predators. Firstly, I show that the switching rule of predators has a significant influence on the expected predator equilibrium distribution in such a dynamic system. Three rules are compared; for all rules, analytical solutions are calculated (where possible). To test their plausibility for natural situations, predator distributions are simulated given the assumption that each predator obtains individual patch profitability estimates by using a common learning rule. As long as prey arrive in the patches in constant numbers per time unit, the first rule leads to input matching because predators stop switching when consumption in the two patches is equal. The other two rules, where predators continue to sample both patches even in the equilibrium state, lead to predator distributions where the more profitable patch is underused. The final equilibrium depends on the exact assumptions of the switching rule; however, it is independent of interference. But if the input delivered into a patch is a function of the current prey standing crop (for example in a reproducing prey population), predator and prey distributions will not reach an equilibrium in most cases: either standing crops increase indefinitely, or they approach zero, with all predators concentrating on the better patch. Only a small number of parameter sets show intermediate crops that are reasonably stable. With this input type, only up to 54% of the simulations reach the expected distribution. In a system with competition for dynamic standing crop, it is therefore essential to know the type of input and the switching-rule used by predators to be able to predict equilibrium predator distributions. Received: 17 March 1995/Accepted after revision: 5 November 1995     

Predator and prey space use: dragonflies and tadpoles in an interactive game

Predator and prey spatial distributions have important population and community level consequences. However, little is known either theoretically or empirically about behavioral mechanisms that underlie the spatial patterns that emerge when predators and prey freely interact. We examined the joint space use and behavioral rules governing movement of freely interacting groups of odonate (dragonfly) predators and two size classes of anuran (tadpole) prey in arenas containing two patches with different levels of the prey's resource. Predator and prey movement and space use was quantified both when they were apart and together. When apart from predators, large tadpoles strongly preferred the high resource patch. When apart from prey, dragonflies weakly preferred the high resource patch. When together, large prey shifted to a uniform distribution, while predators strongly preferred the high resource patch. These patterns qualitatively fit the predictions of several three trophic level, ideal free distribution models. In contrast, the space use of small prey and predators did not deviate from uniform. Three measures of joint space use (spatial correlations, overlap, and co-occurrence) concurred in suggesting that prey avoidance of predators was more important than predator attraction to prey in determining overall spatial patterns. To gain additional insight into behavioral mechanisms, we used a model selection approach to identify behavioral movement rules that can potentially explain the observed, emergent patterns of space use. Prey were more likely to leave patches with more predators and more conspecific competitors; resources had relatively weak effects on prey movements. In contrast, predators were more likely to leave patches with low resources (that they do not consume) and more competing predators; prey had relatively little effect on predator movements. These results highlight the importance of investigating freely interacting predators and prey, the potential for simple game theory models to predict joint spatial distributions, and the utility of using model choice methods to identify potential key factors that govern movement.     

Indirect effects of prey swamping: differential seed predation during a bamboo masting event

Resource pulses often involve extraordinary increases in prey availability that "swamp" consumers and reverberate through indirect interactions affecting other community members. We developed a model that predicts predator-mediated indirect effects induced by an epidemic prey on co-occurring prey types differing in relative profitability/preference and validated our model by examining current-season and delayed effects of a bamboo mass seeding event on seed survival of canopy tree species in mixed Patagonian forests. The model shows that predator foraging behavior, prey profitability, and the scale of prey swamping influence the character and strength of short-term indirect effects on various alternative prey. When in large prey-swamped patches, nonselective predators decrease predation on all prey types. Selective predators, instead, only benefit prey of similar quality to the swamping species, while very low or high preference prey remain unaffected. Negative indirect effects (apparent competition) may override such positive effects (apparent mutualism), especially for highly preferred prey, when prey-swamped patches are small enough to allow predator aggregation and/or predators show a reproductive numerical response to elevated food supply. Seed predation patterns during bamboo (Chusquea culeou) masting were consistent with predicted short-term indirect effects mediated by a selective predator foraging in large prey-swamped patches. Bamboo seeds and similarly-sized Austrocedrus chilensis (ciprés) and Nothofagus obliqua (roble) seeds suffered lower predation in bamboo flowered than nonflowered patches. Predation rates on the small-seeded Nothofagus dombeyi (coihue) and the large-seeded Nothofagus alpina (rauli) were independent of bamboo flowering. Indirect positive effects were transient; three months after bamboo seeding, granivores preyed heavily upon all seed types, irrespective of patch flowering condition. Moreover, one year after bamboo seeding, predation rates on the most preferred seed (rauli) was higher in flowered than in nonflowered patches. Despite rapid predator numerical responses, short-term positive effects can still influence community recruitment dynamics because surviving seeds may find refuge beneath the litter produced by bamboo dieback. Together, our theoretical analysis and experiments indicate that indirect effects experienced by alternative prey during and after prey-swamping episodes need not be universal but can change across a prey quality spectrum, and they critically depend on predator-foraging rules and the spatial scale of swamping.     

Nest defense and central place foraging: A model and experiment

Summary A graphical model presented here indicates that a nest-defending forager should stay closer to its nest, forage for shorter times per patch, and deliver smaller loads than predicated for delivery rate maximization. The effect is more pronounced farther from the nest, so that if nest defense is especially important, the predator should leave far patches sooner than near ones, and deliver smaller loads from farther away. Moreover, if the attack rate at the nest is increased, the defending forager should move closer and deliver smaller prey.Experimental attacks with stuffed specimens at Gila woodpecker (Melanerpes uropygialis) nests produced the predicted changes in the foraging behavior of males, but not of females.Mated pairs may work as a team to pursue simultaneously two conflicting goals—food delivery and nest protection—both of which affect the survivorship of the young. Sexual dimorphism in monogamous species may result in part from specialization in these roles.     

Modelling dispersal with diffusion and habitat selection: Analytical results for highly fragmented landscapes

Quantifying dispersal is crucial both for understanding ecological population dynamics, and for gaining insight into factors that affect the genetic structure of populations. The role of dispersal becomes pronounced in highly fragmented landscapes inhabited by spatially structured populations. We consider a landscape consisting of a set of habitat patches surrounded by unsuitable matrix, and model dispersal by assuming that the individuals follow a random walk with parameters that may be specific to the habitat type. We allow for spatial variation in patch quality, and account for edge-mediated behavior, the latter meaning that the individuals bias their movement towards the patches when close to an edge between a patch and the matrix. We employ a diffusion approximation of the random walk model to derive analytical expressions for various characteristics of the dispersal process. For example, we derive formulae for the time that an individual is expected to spend in its current patch i, and for the time that it will spend in the matrix, both conditional on the individual hitting next a given patch j before hitting any of the other patches or dying. The analytical formulae are based on the assumptions that the landscape is infinitely large, that the patches are circularly shaped, and that the patches are small compared to interpatch distances. We evaluate the effect of these assumptions by comparing the analytical results to numerical results in a real patch network that violates all of the three assumptions. We then consider a landscape that fulfills the assumptions, and show that in this case the analytical results are in a very good agreement with the numerical results. The results obtained here allow the construction of computationally efficient dispersal models that can be used as components of metapopulation models.     

Competitive exclusion within the predator community influences the distribution of a threatened prey species

While much effort has been made to quantify how landscape composition influences the distribution of species, the possibility that geographical differences in species interactions might affect species distributions has received less attention. Investigating a predator-prey setting in a boreal forest ecosystem, we empirically show that large-scale differences in the predator community structure and small-scale competitive exclusion among predators affect the local distribution of a threatened forest specialist more than does landscape composition. Consequently, even though the landscape parameters affecting Siberian flying squirrel (Pteromys volans) distribution (prey) did not differ between nest sites of the predators Northern Goshawks (Accipiter gentilis) and Ural Owls (Strix uralensis), flying squirrels were heterospecifically attracted by goshawks in a region where both predator species were present. No such effect was found in another region where Ural Owls were absent. These results provide evidence that differences in species interactions over large spatial scales may be a major force influencing the distribution and abundance patterns of species. On the basis of these findings, we suspect that subtle species interactions might be a central reason why landscape models constructed to predict species distributions often fail when applied to wider geographical scales.     

Effects of density-dependent dispersal behaviours on the speed and spatial patterns of range expansion in predator-prey metapopulations

Dispersal can strongly affect the spatiotemporal dynamics of a species (its spread, spatial distribution and persistence). We investigated how two dispersal behaviours, namely prey evasion (PE) and predator pursuit (PP), affect the dynamics of a predator-prey system. PE portrays the tendency of prey avoiding predators by dispersing into adjacent patches with fewer predators, while PP describes the tendency of predators to pursue the prey by moving into patches with more prey. Based on the Beddington predation model, a spatially explicit metapopulation model was built to incorporate PE and PP. Numerical simulations were run to investigate the effects of PE and PP on the rate of spread, spatial synchrony and the persistence of populations. Results show that both PE and PP can alter spatial synchrony although PP has a weaker desynchronising effect than PE. The predator-prey system without PE and PP expanded in circular waves. The effect of PE can push the prey to distribute in a circular ring front, whereas the effect of PP can change the circular waves to anisotropic expansion. Furthermore, weak PE and PP can accelerate the spread of prey while strong and disproportionate intensities slow down the range expansion. The effects of PE and PP further enhance the population size, break down the spatial synchrony and promote the persistence of populations.     

Predators, parasitoids, and pathogens: a cross-cutting examination of intraguild predation theory

Although the canonical concept of intraguild predation evokes images of predators and prey, several subdisciplines within ecology have developed theory not specifically framed in terms of predation and competition and often using system-specific terminology, yet functionally quite similar. Here, we formulate models combining exploitation and competition in predator-prey, host-parasitoid, and host-pathogen communities to compare dynamics, food web structure, and coexistence criteria for these disparate communities. Although dynamic stability in the coexistence region varies strongly among systems, in all cases coexistence of two consumers on a single resource occurs only if the intraguild prey species is more efficient than the intraguild predator at suppressing the abundance of the basal resource, and if the intraguild predator accrues a sufficient gain from attacking the intraguild prey. In addition, equilibrial abundances of all species in all three formulations respond similarly to increases in productivity of the basal resource. Our understanding of predator-prey and parasitoid-host communities has benefited from explicit examination of intraguild predation (IGP) theory, and we suggest that future research examining pathogen communities, in particular, will benefit substantially from explicit recognition of predictions from IGP theory.     

Contribution of Roads to Forest Fragmentation in the Rocky Mountains

The contribution of roads to forest fragmentation has not been adequately analyzed. We quantified fragmentation due to roads in a 30,213-ha section of the Medicine Bow-Routt National Forest in sout heastern Wyoming with several indices of landscape structure using a geographic information system. The number of patches, mean patch area, mean interior area, mean area of edge influence, mean patch perimeter, total perimeter, and mean patch shape identified patch- and edge-related landscape changes. Shannon-Wiener diversity, dominance, contagion, contrast, and angular second moment indicated effects on landscape diversity and texture. Roads added to forest fragmentation more than clearcuts by dissecting large patches into smaller pieces and by converting forest interior habitat into edge habitat. Edge habitat created by roads was 1.54–1.98 times the edge habitat created by clearcuts. The total landscape area affected by clearcuts and roads was 2.5–3.5 times the actual area occupied by these disturbances. Fragmentation due to roads could be minimized if road construction is minimized or rerouted so that its fragmentation effects are reduced. Geographic information system technology can be used to quantify the potential fragmentation effects of individual roads and the cumulative effects of a road network on landscape structure.     

Obstruction of biodiversity conservation by minimum patch size criteria

Minimum patch size criteria for habitat protection reflect the conservation principle that a single large (SL) patch of habitat has higher biodiversity than several small (SS) patches of the same total area (SL > SS). Nonetheless, this principle is often incorrect, and biodiversity conservation requires placing more emphasis on protection of large numbers of small patches (SS > SL). We used a global database reporting the abundances of species across hundreds of patches to assess the SL > SS principle in systems where small patches are much smaller than the typical minimum patch size criteria applied for biodiversity conservation (i.e., ∼85% of patches <100 ha). The 76 metacommunities we examined included 4401 species in 1190 patches. From each metacommunity, we resampled species–area accumulation curves to evaluate how biodiversity responded to habitat existing as a few large patches or as many small patches. Counter to the SL > SS principle and consistent with previous syntheses, species richness accumulated more rapidly when adding several small patches (45.2% SS > SL vs. 19.9% SL > SS) to reach the same cumulative area, even for the very small patches in our data set. Responses of taxa to habitat fragmentation differed, which suggests that when a given total area of habitat is to be protected, overall biodiversity conservation will be most effective if that habitat is composed of as many small patches as possible, plus a few large ones. Because minimum patch size criteria often require larger patches than the small patches we examined, our results suggest that such criteria hinder efforts to protect biodiversity.     

Threat-sensitive predator avoidance in damselfish-trumpetfish interactions

Summary Predatory threat can vary during a predator-prey interaction as an attack escalates or among predators at different times. A Threat-sensitivity hypothesis is presented which predicts that prey individuals will trade-off predator avoidance against other activities by altering their avoidance responses in a manner that reflects the magnitude of the predatory threat. This hypothesis was tested in the field by presenting prey (threespot damselfish, Stegastes planifrons) with models of foraging predators (Atlantic trumpetfish, Aulostomus maculatus). During a presentation, damselfish displayed progressively stronger avoidance as predator models were brought nearer; response waned rapidly once predator models passed overhead. Larger predator models and those oriented in a strike pose evoked stronger avoidance reactions than smaller and non-attacking models, intermediate responses were evoked by size and orientation combinations that were intermediate in threat, and habituation was more common to weakly-threatening presentations. Smaller damselfish showed stronger avoidance of models than did larger damselfish. Nonavoidance activities, such as feeding and territorial defense, were curtailed during presentations or were more common during weakly threatening presentations. Approaches to the models, equated with mobbing, were more common among large damselfish, again reflecting degrees of vulnerability among different size prey individuals. These initial results indicate that damselfish threatened by predators respond in a graded manner that reflects the degree of threat posed by the predator, in accordance with the Threat-sensitivity hypothesis.     

Impact of cannibalism on predator-prey dynamics: size-structured interactions and apparent mutualism

Direct and indirect interactions between two prey species can strongly alter the dynamics of predator-prey systems. Most predators are cannibalistic, and as a consequence, even systems with only one predator and one prey include two prey types: conspecifics and heterospecifics. The effects of the complex direct and indirect interactions that emerge in such cannibalistic systems are still poorly understood. This study examined how the indirect interaction between conspecific and heterospecific prey affects cannibalism and predation rates and how the direct interactions between both species indirectly alter the effect of the cannibalistic predator. I tested for these effects using larvae of the stream salamanders Eurycea cirrigera (prey) and Pseudotriton ruber (cannibalistic predator) by manipulating the relative densities of the conspecific and heterospecific prey in the presence and absence of the predator in experimental streams. The rates of cannibalism and heterospecific predation were proportional to the respective densities and negatively correlated, indicating a positive indirect interaction between conspecific and heterospecific prey, similar to "apparent mutualism." Direct interactions between prey species did not alter the effect of the predator. Although both types of prey showed a similar 30% reduction in night activity and switch in microhabitat use in response to the presence of the predator, cannibalism rates were three times higher than heterospecific predation rates irrespective of the relative densities of the two types of prey. Cumulative predation risks differed even more due to the 48% lower growth rate of conspecific prey. Detailed laboratory experiments suggest that the 3:1 difference in cannibalism and predation rate was due to the higher efficiency of heterospecific prey in escaping immediate attacks. However, no difference was observed when the predator was a closely related salamander species, Gyrinophilus porphyriticus, indicating that this difference is species specific. This demonstrates that cannibalism can result in the coupling of predator and prey mortality rates that strongly determines the dynamics of predator-prey systems.     

Behavioural responses to indirect and direct predator cues by a mammalian herbivore, the common brushtail possum

Cues for detecting and responding to perceived predation risk may be indirect, i.e., correlated with the probability of encountering a predator, or direct, i.e., produced by or related to the actual presence of a predator. Research shows, independently, both types of cues can influence anti-predator and foraging behaviours in prey species. However, since animals naturally encounter indirect and direct cues simultaneously, we were interested in quantifying their cumulative effect. Our aim was to evaluate food intake and behaviours (patch use, feeding (rate and time), vigilance) of a nocturnal mammalian herbivore to indirect (open vs. covered microhabitats; illumination) and direct (fox/owl odours) predator cues. We ran a preference trial with four paired treatments using a covered Safe food patch and an open Risk food patch, with one of four combinations of indirect and direct predator cues. Predation risk had a significant effect on both intake and behaviour (including feeding time, rate, and vigilance), but these effects differed depending on cues. No two combinations of cues produced exactly the same effects, illustrating the complexity of interactions that occur between cues. Covered patches were always perceived as less risky than open patches, but unexpectedly, open patches were perceived as riskier when dark rather than light. The strongest suite of (negative) responses to risk was associated with combined indirect and direct cues. These results highlight the importance of considering jointly, intake from a patch, intake rate, and behaviours, such as the proportion of time spent vigilant, when quantifying predation risk, rather than intake alone.     

Patch use and vigilance by sympatric lemmings in predator and competitor-driven landscapes of fear

Prey living in risky environments can adopt a variety of behavioral tactics to reduce predation risk. In systems where predators regulate prey abundance, it is reasonable to assume that differential patterns of habitat use by prey species represent adaptive responses to spatial variation in predation. However, patterns of habitat use also reflect interspecific competition over habitat. Collared (Dicrostonyx groenlandicus) and brown (Lemmus trimucronatus) lemmings represent such a system and possess distinct upland tundra versus mesic meadow habitat preferences consistent with interspecific competition. Yet, we do not know whether this habitat preference might also reflect differences in predation risk or whether the two species differ in their behavioral tactics used to avoid predation. We performed experiments where we manipulated putative predation risk perceived by lemmings by increasing protective cover in upland and meadow habitats while we recorded lemming activity and behavior. Both lemming species preferentially used cover more than open patches, but Dicrostonyx was more vigilant than Lemmus. Both species also constrained their activity to protective patches in upland and meadow habitats, but during different periods of the day. Use of cover and vigilance were independent of habitat, suggesting that both species live in a fearsome but flattened landscape of fear at Walker Bay (Nunavut, Canada), and that their habitat preference is a consequence of competition rather than predation risk. Future studies aiming to map the contours of fear in multi-prey–predator systems should consider how predation and competition interact to modify prey species’ habitat preference, patch use, and vigilance.     

Harvest policies and nonmarket valuation in a predator — prey system

Although prey may not have commercial value, their economic value can be ascertained in a predator-prey model if the predator has a harvest value. The economic optimal (recovery) path of the predator and prey are carefully described when growth is quadratic in the predator (prey) and linear in prey (predator). Parameter values, in part, resembling Pacific halibut are used to provide numerical illustrations.     

Landscape of fear influences the relative importance of consumptive and nonconsumptive predator effects

Predators can initiate trophic cascades by consuming and/or scaring their prey. Although both forms of predator effect can increase the overall abundance of prey's resources, nonconsumptive effects may be more important to the spatial and temporal distribution of resources because predation risk often determines where and when prey choose to forage. Our experiment characterized temporal and spatial variation in the strength of consumptive and nonconsumptive predator effects in a rocky intertidal food chain consisting of the predatory green crab (Carcinus maenas), an intermediate consumer (the dogwhelk, Nucella lapillus), and barnacles (Semibalanus balanoides) as a resource. We tracked the survival of individual barnacles through time to map the strength of predator effects in experimental communities. These maps revealed striking spatiotemporal patterns in Nucella foraging behavior in response to each predator effect. However, only the nonconsumptive effect of green crabs produced strong spatial patterns in barnacle survivorship. Predation risk may play a pivotal role in determining the small-scale distribution patterns of this important rocky intertidal foundation species. We suggest that the effects of predation risk on individual foraging behavior may scale up to shape community structure and dynamics at a landscape level.