Predator Species Richness Research Articles

A conditional trophic cascade: Birds benefit faster growing trees with strong links between predators and plants

Terrestrial systems are thought to be organized predominantly from the bottom-up, but there is a growing literature documenting top-down trophic cascades under certain ecological conditions. We conducted an experiment to examine how arthropod community structure on a foundation riparian tree mediates the ability of insectivorous birds to influence tree growth. We built whole-tree bird exclosures around 35 mature cottonwood (Populus spp.) trees at two sites in northern Utah, USA, to measure the effect of bird predation on arthropod herbivore and predator species richness, abundance, and biomass, and on tree performance. We maintained bird exclosures over two growing seasons and conducted nondestructive arthropod surveys that recorded 63652 arthropods of 689 morphospecies representing 19 orders. Five major patterns emerged: (1) We found a significant trophic cascade (18% reduction in trunk growth when birds were excluded) only at one site in one year. (2) The significant trophic cascade was associated with higher precipitation, tree growth, and arthropod abundance, richness, and biomass than other site-year combinations. (3) The trophic cascade was weak or not evident when tree growth and insect populations were low apparently due to drought. (4) Concurrent with the stronger trophic cascade, bird predation significantly reduced total arthropod abundance, richness, and biomass. Arthropod biomass was 67% greater on trees without bird predation. This pattern was driven largely by two herbivore groups (folivores and non-aphid sap-feeders) suggesting that birds targeted these groups. (5) Three species of folivores (Orthoptera: Melanoplus spp.) were strong links between birds and trees and were only present in the site and the year in which the stronger trophic cascade occurred. Our results suggest that this trophic system is predominately bottom-up driven, but under certain conditions the influence of top predators can stimulate whole tree growth. When the most limiting factor for tree growth switched from water availability to herbivory, the avian predators gained the potential to reduce herbivory. This potential could be realized when strong links between the birds and plant, i.e., species that were both abundant herbivores and preferred prey, were present.

Complementary predation on metamorphosing species promotes stability in predator–prey systems

Functionally redundant predation and functionally complementary predation are both widespread phenomena in nature. Functional complementary predation can be found, for example, when predators feed on different life stages of their prey, while functional redundant predation occurs when different predators feed on all life stages of a shared prey. Both phenomena are common in nature, and the extent of differential life-stage predation depends mostly on prey life history; complementary predation is expected to be more common on metamorphosing prey species, while redundant predation is thought to be higher on non-metamorphosing species. We used an ordinary differential equation model to explore the effect of varying degree of complementary and redundant predation on the dynamic properties of a system with two predators that feed on an age-structured prey. Our main finding was that predation on one stage (adult or juvenile) resulted in a more stable system (i.e., it is stable for a wider range of parameters) compared to when the two predators mix the two prey developmental stages in their diet. Our results demonstrate that predator–prey dynamics depends strongly on predators' functionality when predator species richness is fixed. Results also suggest that systems with metamorphosing prey are expected to be more diverse compared to systems with non-metamorphosing prey.

Plant species loss decreases arthropod diversity and shifts trophic structure

Plant diversity is predicted to be positively linked to the diversity of herbivores and predators in a foodweb. Yet, the relationship between plant and animal diversity is explained by a variety of competing hypotheses, with mixed empirical results for each hypothesis. We sampled arthropods for over a decade in an experiment that manipulated the number of grassland plant species. We found that herbivore and predator species richness were strongly, positively related to plant species richness, and that these relationships were caused by different mechanisms at herbivore and predator trophic levels. Even more dramatic was the threefold increase, from low- to high-plant species richness, in abundances of predatory and parasitoid arthropods relative to their herbivorous prey. Our results demonstrate that, over the long term, the loss of plant species propagates through food webs, greatly decreasing arthropod species richness, shifting a predator-dominated trophic structure to being herbivore dominated, and likely impacting ecosystem functioning and services.

Point Counts Underestimate the Importance of Arctic Foxes as Avian Nest Predators: Evidence from Remote Video Cameras in Arctic Alaskan Oil Fields

We used video cameras to identify nest predators at active shorebird and passerine nests and conducted point count surveys separately to determine species richness and detection frequency of potential nest predators in the Prudhoe Bay region of Alaska. From the surveys, we identified 16 potential nest predators, with glaucous gulls (Larus hyperboreus) and parasitic jaegers (Stercorarius parasiticus) making up more than 80% of the observations. From the video evidence, however, we identified arctic foxes (Alopex lagopus) as the predators in five of six predation events recorded with the cameras. These results indicate that estimated abundances of predators alone may not accurately reflect their true or proportional importance as nest predators. We also found that the identified predators removed all eggs and left the nests intact. Thus, attempts to identify predators solely on the basis of nest remains are not reliable for smaller bird species in this region. We found no evidence that camera-monitored nests were at greater risk of predation or desertion than camera-free nests. Overall, our ability to film predation events was hampered by the brief, highly synchronized breeding season, the harsh climate, and the higher nest survivorship for shorebirds in this region relative to temperate-breeding passerines, which have been the focus of most studies that use camera systems in attempts to identify nest predators at active nests.

Effects of vegetation structure and floristic diversity on detritivore, herbivore and predatory invertebrates within calcareous grasslands

Calcareous grasslands in Europe have shown wide scale declines in their extent and quality as a result of modern agricultural practices, increased atmospheric eutrophication and lack of management. In addition to being a key habitat for specialist plants, calcareous grasslands are also important for many threatened invertebrates. In this UK based study, we investigated the impact of military vehicle activity, floral species richness and vegetation structure on assemblages of detritivore, herbivore and predatory invertebrates. We also consider the impact that disturbance by military vehicle activity on the proportion of invertebrate species capable of flight, a surrogate for dispersal ability. Sward height was negatively correlated with detritivore, herbivore and predator species richness. Herbivores species richness was positively correlated with both forb and grass species richness. Spatial variation in the number of plant species was negatively correlated with herbivore species richness. Those sites most heavily disturbed by military vehicle activity supported the lowest proportions of flightless invertebrates. Successful management for calcareous grassland invertebrates should aim to maintain short swards with high floristic diversity, in terms of both the forbs and grasses. It should be noted, however, that these findings refer to principally surface rather than sward active invertebrates. While disturbance associated with military vehicle activity was not found to affect invertebrate species richness, it has negative consequences for the structure of invertebrate assemblages by selecting against invertebrates with low dispersal ability. To support invertebrate diversity in calcareous grasslands we emphasise the need for variety in the timing and type of management applied to promote heterogeneity in sward structure.

Community consequences of herbivore‐induced bottom–up trophic cascades: the importance of resource heterogeneity

1. Herbivory often changes resource quality for herbivorous insects through induced plant responses depending on the intensity of damage. We hypothesized that the willow's response following herbivory affects the entire arthropod community structure on the tree due to changes in plant quality. To examine this hypothesis, we investigated arthropod communities on three willow species, Salix gilgiana, Salix eriocarpa and Salix serissaefolia. 2. In our common garden, cuttings were established in 2003 and experimental treatments were applied in 2005. Damage by a boring caterpillar of a swift moth (Endoclita excrescens) and artificial cutting of 25% stems were applied as partial herbivory within individual trees, and 100% cutting of stems was applied to represent severe herbivory to whole individual trees. These treatments stimulated lateral shoot production depending on damage intensity, resulting in full compensation for biomass loss. 3. Positive relationships were detected between within-tree variation in foliar nitrogen content and overall abundance/species richness of herbivores. Moth boring and 25% cutting increased herbivore abundance and species richness relative to controls. However, we found no significant differences in herbivore abundance and species richness between 100% cut and control trees. Community composition of herbivore species was significantly different between the following three groups: (i) bored and 25% cut; (ii) 100% cut; and (iii) control trees. Changes in community structure of herbivores were likely due to changes in plant quality depending on the intensity of damage. 4. Although total predator abundance and species richness were not significantly different among treatments, community composition of predator species was significantly different among treatments. 5. These results indicate that herbivore-induced willow responses can largely determine the entire arthropod community structure of multitrophic levels due to changes in plant quality. We suggest that heterogeneous resource conditions induced by herbivory within and among plant individuals increase the species diversity of arthropods.

Predator richness has no effect in a diverse marine food web

1. In many ecosystems, predator abundance, composition and diversity vary naturally among seasons and habitats. In addition, predator assemblages are changing due to overharvesting, habitat destruction and species invasions. 2. Predator species composition and richness can influence prey community structure and these effects can cascade to influence plant abundance and composition. 3. To test the effects of predator presence, composition and species richness on prey abundance, species richness and composition, we conducted three experiments in a subtidal marine food web. Experimental food webs were drawn from species pools of 5-7 predator species, 19-52 prey species, benthic micro-algae and 5 macro-algae. 4. Predators reduced prey abundance in the mesocosm experiment, but this effect was diminished or absent in field experiments. Predator species differed in their effects on prey, but we found no effect of predator richness (via complementarity or selection) on any aspect of prey community structure. 5. The absence of a predator richness effect could be due to several factors including potentially opposing effects of individual predator species, intraguild predation, or greater importance of colonization relative to competition in structuring prey assemblages. Although predators can have strong top-down effects in this system, selection or resource-use complementarity among predators do not affect prey community structure.

Effects of nitrogen application on beetle communities in tea plantations

AbstractIn contrast to grassland and forest ecosystems, little is known about insect response to nitrogen deposition in agricultural ecosystems. This study was carried out to investigate the effects of short‐term (1–2 years) nitrogen application (0, 172.5, 345.0, 690.0, and 1035.0 kg · N ha−1· y−1) on beetle communities in tea plantations. A collection of 34 families, 89 species of beetles, was obtained from a tea plantation in Wuyishan, China. Among them, herbivores, predators and detritivores had 52, 29, and eight species, respectively. Species richness, effective diversity and abundance (measured as the number of individuals and insect biomass) of the beetle community were not significantly related to the rate of nitrogen application. However, nitrogen application changed the species distribution and weakly increased the evenness of species distribution, while this did not significantly change the species evenness. Species richness and abundance of herbivores and predators were not significantly related to the rate of nitrogen application. However, there were some variations in trophic responses to nitrogen. Species richness and abundance of detritivores increased with increasing nitrogen application.

Are there direct and cascading effects of changes in grazer and predator species richness in a model system with heterogeneously distributed resources?

The consequences of biodiversity loss on ecosystem processes and services have attracted substantial scientific effort over the last two decades. Most experiments have been small-scale and aimed to minimise environmental heterogeneity. Environmental heterogeneity is, however, known to be important in mediating species coexistence in both space and time. In an attempt to evaluate the potential importance of herbivore and predator richness in controlling the biomass and evenness of lower trophic levels, we manipulated the number of coexisting consumer species in a marine algae-grazer-predator microcosm system with a heterogeneous resource base. We performed two experiments where we manipulated the richness of four grazers and one where the richness of two predators, one crab and one shrimp, was manipulated. Even though the algal assemblage was diverse and potentially allowed for resource partitioning among grazers, plant consumption was mostly an effect of one effective grazer: the gastropod Littorina littorea. There were no significant richness effects on grazing rates of having four coexisting grazer species: the mixture with four grazers was approximately equal to the average of the four monocultures. Similarly, there was no emergent effect with two predator species present, as opposed to one species. The crab was most efficient in decreasing grazer biomass, whereas the effect of the shrimp was much weaker. Predators did not have any cascading effects on the algal community. In line with previous research, our results suggest that resource heterogeneity must be accompanied by broad enough trait diversity in order for resource partitioning to occur.

Effects of stream predator richness on the prey community and ecosystem attributes

It is important to understand the role that different predators can have to be able to predict how changes in the predator assemblage may affect the prey community and ecosystem attributes. We tested the effects of different stream predators on macroinvertebrates and ecosystem attributes, in terms of benthic algal biomass and accumulation of detritus, in artificial stream channels. Predator richness was manipulated from zero to three predators, using two fish and one crayfish species, while density was kept equal (n = 6) in all treatments with predators. Predators differed in their foraging strategies (benthic vs. drift feeding fish and omnivorous crayfish) but had overlapping food preferences. We found effects of both predator species richness and identity, but the direction of effects differed depending on the response variable. While there was no effect on macroinvertebrate biomass, diversity of predatory macroinvertebrates decreased with increasing predator species richness, which suggests complementarity between predators for this functional feeding group. Moreover, the accumulation of detritus was affected by both predator species richness and predator identity. Increasing predator species richness decreased detritus accumulation and presence of the benthic fish resulted in the lowest amounts of detritus. Predator identity (the benthic fish), but not predator species richness had a positive effect on benthic algal biomass. Furthermore, the results indicate indirect negative effects between the two ecosystem attributes, with a negative correlation between the amount of detritus and algal biomass. Hence, interactions between different predators directly affected stream community structure, while predator identity had the strongest impact on ecosystem attributes.

Herbivore and predator diversity interactively affect ecosystem properties in an experimental marine community

Interacting changes in predator and prey diversity likely influence ecosystem properties but have rarely been experimentally tested. We manipulated the species richness of herbivores and predators in an experimental benthic marine community and measured their effects on predator, herbivore and primary producer performance. Predator composition and richness strongly affected several community and population responses, mostly via sampling effects. However, some predators survived better in polycultures than in monocultures, suggesting complementarity due to stronger intra- than interspecific interactions. Predator effects also differed between additive and substitutive designs, emphasizing that the relationship between diversity and abundance in an assemblage can strongly influence whether and how diversity effects are realized. Changing herbivore richness and predator richness interacted to influence both total herbivore abundance and predatory crab growth, but these interactive diversity effects were weak. Overall, the presence and richness of predators dominated biotic effects on community and ecosystem properties.

SIMULATED PREDATOR EXTINCTIONS: PREDATOR IDENTITY AFFECTS SURVIVAL AND RECRUITMENT OF OYSTERS

The rate of species loss is increasing at a global scale, and human-induced extinctions are biased toward predator species. We examined the effects of predator extinctions on a foundation species, the eastern oyster (Crassostrea virginica). We performed a factorial experiment manipulating the presence and abundance of three of the most common predatory crabs, the blue crab (Callinectes sapidus), stone crab (Menippe mercenaria), and mud crab (Panopeus herbstii) in estuaries in the eastern United States. We tested the effects of species richness and identity of predators on juvenile oyster survival, oyster recruitment, and organic matter content of sediment. We also manipulated the density of each of the predators and controlled for the loss of biomass of species by maintaining a constant mass of predators in one set of treatments and simultaneously using an additive design. This design allowed us to test the density dependence of our results and test for functional compensation by other species. The identity of predator species, but not richness, affected oyster populations. The loss of blue crabs, alone or in combination with either of the other species, affected the survival rate of juvenile oysters. Blue crabs and stone crabs both affected oyster recruitment and sediment organic matter negatively. Mud crabs at higher than ambient densities, however, could fulfill some of the functions of blue and stone crabs, suggesting a level of ecological redundancy. Importantly, the strong effects of blue crabs in all processes measured no longer occurred when individuals were present at higher-than-ambient densities. Their role as dominant predator is, therefore, dependent on their density within the system and the density of other species within their guild (e.g., mud crabs). Our findings support the hypothesis that the effects of species loss at higher trophic levels are determined by predator identity and are subject to complex intraguild interactions that are largely density dependent. Understanding the role of biodiversity in ecosystem functioning or addressing practical concerns, such as loss of predators owing to overharvesting, remains complicated because accurate predictions require detailed knowledge of the system and should be drawn from sound experimental evidence, not based on observations or generalized models.

Biotic integrity of the arthropod communities in the natural forests of Azores

The loss of biotic integrity in ecosystems due to human pressure has been receiving much attention from the scientific community. The primary aim of this study is to understand how the increasing human pressure on natural forests in the Azorean archipelago (North Atlantic) is affecting their epigean arthropod communities and which biological parameters it affects most. An expert team did fieldwork covering most of the natural forests (mainly inside nature reserves) of the archipelago using standardized pitfall trapping. To build a multimetric index we tested a number of taxonomic and ecological parameters that can potentially be influenced by disturbance. Sixteen of these were found to be significantly influenced by disturbance in forests. We retained seven metrics due to both, desirable scalability properties and relatively low correlation between them. These included the percentages of endemic and predator species richness and also predator abundance, which are inversely related to disturbance; and the percentages of native and saprophagous species richness and introduced and herbivore abundance, which are positively related to disturbance. All seven metrics were combined in an Index of Biotic Integrity (IBI) value. We then proceeded to understand which potential disturbance factors are influencing the biotic integrity of communities and how such influence is felt. Five disturbance factors were found to influence the IBI, although in different ways: the size and fragmentation of reserves, the distance of sites to the reserve borders, the invasion by alien plants and the density of human paths at the sites. Given that only percentages of taxonomical or ecological characteristics were chosen as metrics, we tested and found the scalability of the IBI to be possible, allowing the comparison of sites with different collecting effort or even the comparison of reserves with different areas and numbers of collecting sites in each. Finally, we propose a novel graphical representation for multimetric indices like the IBI, one which allows retaining much of the information that is usually lost in multimetric indices.

Influences of Habitat Isolation on Invertebrate Colonization of Sporadanthus ferrugineus in a Mined Peat Bog

Abstract This study experimentally tested the impact of peat bog habitat loss and isolation on the invertebrate community associated with Sporadanthus ferrugineus (Restionaceae), a dominant indigenous plant species in peat bogs. Potted S. ferrugineus plants were exposed to invertebrates at various distances up to 800 m from an intact habitat (the source population) over 18 weeks. Invertebrates rapidly colonized the experimental plants, with all major orders and trophic groups present on S. ferrugineus within 6 weeks. However, with increasing distance away from the undisturbed habitat, there was a significant decrease in total species richness and abundance of invertebrates associated with the potted plants. Of the total taxa captured, only 38% were found on potted S. ferrugineus plants at 800 m compared with 62% found on potted plants 30 m from the intact peat bog. Predator species richness and the predator–prey ratio changed significantly with time available for colonization of potted plants but, more importantly, prey (herbivores and detritivores) and predator (including parasitoids) species richness, as well as the predator–prey ratio, declined significantly with increasing isolation from the peat bog. Thus, the degree of isolation of restoration areas from undisturbed habitat has a major impact on the rate and patterns of recovery in invertebrate community structure. The current recommended practice of restoring the mined area by establishing raised “habitat islands” 30 m apart should result in colonization by most invertebrates associated with S. ferrugineus, but only if the restoration islands are placed as stepping stones outward from existing areas of intact habitat.

SPECIES IDENTITY DOMINATES THE RELATIONSHIP BETWEEN PREDATOR BIODIVERSITY AND HERBIVORE SUPPRESSION

Agricultural pest suppression is an important ecosystem service that may be threatened by the loss of predator diversity. This has stimulated interest in the relationship between predator biodiversity and biological control. Multiple-predator studies have shown that predators may complement or interfere with one another, but few experiments have determined if the resulting effects on prey are caused by changes in predator abundance, identity, species richness, or some combination of these factors. We experimentally isolated the effect of predator species richness on the biological control of an important agricultural pest, the green peach aphid. We found no evidence that increasing predator species richness affects aphid biological control; overall there was no strong complementarity or interference among predator species that altered the strength of aphid suppression. Instead, our experiments revealed strong effects of predator species identity, because predators varied dramatically in their per capita consumption rates. Our results are consistent with other multiple-predator studies finding strong species-identity effects and suggest that, for the biological control of aphids, conservation strategies that directly target key species will be more effective than those targeting predator biodiversity more broadly.

Predator diversity and the functioning of ecosystems: the role of intraguild predation in dampening trophic cascades

AbstractSingle trophic‐level studies of the relationship between biodiversity and ecosystem functioning highlight the importance of mechanisms such as resource partitioning, facilitation, and sampling effect. In a multi‐trophic context, trophic interactions such as intraguild predation may also be an important mediator of this relationship. Using a salt‐marsh food web, we investigated the interactive effects of predator species richness (one to three species) and trophic composition (strict predators, intraguild predators, or a mixture of the two) on ecosystem functions such as prey suppression and primary production via trophic cascades. We found that the trophic composition of the predator assemblage determined the impact of increasing predator species richness on the occurrence of trophic cascades. In addition, increasing the proportion of intraguild predator species present diminished herbivore suppression and reduced primary productivity. Therefore, trophic composition of the predator assemblage can play an important role in determining the nature of the relationship between predator diversity and ecosystem function.

Functional benefits of predator species diversity depend on prey identity

Abstract. 1. Determining the functional significance of species diversity in natural enemy assemblages is a key step towards prediction of the likely impact of biodiversity loss on natural pest control processes. While the biological control literature contains examples in which increased natural enemy diversity hinders pest control, other studies have highlighted mechanisms where pest suppression is promoted by increased enemy diversity.2. This study aimed to test whether increased predator species diversity results in higher rates of predation on two key, but contrasting, insect pest species commonly found in the rice ecosystems of south‐east Asia.3. Glasshouse experiments were undertaken in which four life stages of a planthopper (Nilaparvata lugens) and a moth (Marasmia patnalis) were caged with single or three‐species combinations of generalist predators.4. Generally, predation rates of the three‐species assemblages exceeded expectation when attackingM. patnalis, but not when attackingN. lugens.In addition, a positive effect of increased predator species richness on overall predation rate was found withM. patnalisbut not withN. lugens.5. The results are consistent with theoretical predictions that morphological and behavioural differentiation among prey life stages promotes functional complementarity among predator species. This indicates that emergent species diversity effects in natural enemy assemblages are context dependent; they depend not only on the characteristics of the predators species, but on the identity of the species on which they prey.

Patterns of Avian Nest Predators and a Brood Parasite Among Restored Riparian Habitats in Agricultural Watersheds

In fragmented edge-dominated landscapes, nest predation and brood parasitism may reduce avian reproductive success and, ultimately, populations of some passerine species. In the fragmented agroecosystem of northwest Mississippi, placement of drop-pipe structures has been used as a restoration technique for abating gully erosion along stream banks. These actions have formed small herbaceous and woody habitat extensions into former agricultural lands. We quantified species relative abundances, species richness, and evenness of avian nest predators and a brood parasite within four categories of constructed habitat resulting from drop-pipe installation. Differences in the abundance of two nest predators, cotton mouse (Peromyscus gossypinus) and blue jay (Cyanocitta cristata), were observed among constructed habitats. However, relative abundances of other predators such as common grackle (Quiscalus quiscula), American crow (Corvus brachyrhynchos), and hispid cotton rat (Sigmodon hispidus), and the obligate brood parasite brown-headed cowbird (Molothrus ater) did not differ among four habitat categories. Although species richness, abundance, and evenness of potential nest predators were generally similar among the constructed habitats, predator species composition varied, suggesting that these habitats supported different predator communities. This difference is important because as each predator species is added to or deleted from the community, variation may occur in the framework of prey search methods, predator strategies, and potentially overall predation pressure. We suggest that land managers using drop-pipes as part of stream restoration projects allow for the development of the constructed habitat with the largest area and greatest vegetative structure.

Estimating the prevalence and strength of non-independent predator effects

Understanding whether multiple predator species have independent effects on shared prey is critical for understanding community dynamics. We describe the prevalence and strength of non-independence between predators by quantifying the prey's risk of predation and the degree to which it deviates from the risk predicted from a null model of independent predator effects. Specifically, we document how frequently non-independent effects occur among ten different multiple predator combinations with mayfly larvae as prey. These predator combinations vary both predator density and predator species richness. Overall, the predator effects were non-independent and translated to an average of 27% fewer prey being consumed compared to independent predator effects. Non-independence of this magnitude is likely to have population level consequences for the prey and influence the distribution or prey preference of predators. Closer inspection shows that much of the risk reduction in this system is weak, to the point of being indistinguishable from independent predator effects, while few effects are strong. This pattern of many weak interactions and few strong ones parallels the pattern of interaction strengths documented previously in intertidal communities. Consequently, understanding strong interactors in multiple predator systems may help us understand the importance of a species.

Edge effects on nest predators in two forested landscapes

Few studies have systematically examined edge effects on nest predators, although many invoke these processes as potential mechanisms for decreased nesting success of songbirds. Species richness and relative abundance of avian and mammalian nest predators were compared between forest edge and interior in two landscapes, Allegan State Game Area and Fort Custer Training Center (FCTC), in southwest Michigan. One avian predator, the American crow (Corvus brachyrhynchos Brehm, 1822), was more abundant at edges than forest interior at FCTC; however, other predators did not demonstrate an edge response. Abundance of the brood parasite (Molothrus ater (Boddaert, 1783)) was greater at edges in FCTC. Overall abundance was higher at FCTC in both years; however, this could not be attributed to a greater extent of fragmentation. Total species richness for both landscapes did not differ between edge and interior. Remote-camera systems captured three predation events, two involving red squirrels (Tamiasciurus hudsonicus (Erxleben, 1777)) and one involving a blue jay (Cyanocitta cristata (L., 1758)). Vegetation characteristics were similar between edge and interior sites, which suggests that vegetation structure did not influence edge response. The variability in response indicates a need to assess patterns of predator distributions through long-term studies at multiple spatial scales.