Prey Escape Direction is Influenced by the Pivoting Displays of Flush-Pursuing Birds

Painted redstart, Myioborus pictus, and its congeners in Central and South America, belong to a small fraction of insectivorous flush‐pursuing birds. Unlike most of the small insectivorous birds, which glean prey from substrates, the flush pursuers spread and pivot their conspicuously patterned tails and wings. This display triggers prey escape flights which are hypothesized to occur through visual stimulation of prey escape circuits [giant descending neuron cluster (GDNC) in Diptera] sensitive to the looming motion of an approaching bird, translational motion of a pivoting body with widely spread tail and contrast of the white‐black plumage pattern. In this paper, data from field observations of redstarts and experiments with bird models show an increase in the frequency of prey escapes away from the strong visual stimulation of an open tail, and in the direction opposite to that of the horizontal translational motion present in the pivots. We discuss how the effect on prey escape direction may enhance prey interception capabilities of redstarts during aerial pursuits. Combined with an earlier study the results show that, unlike the movements of typical gleaner–foragers, the flush displays by redstarts affect prey escape direction in a manner that may facilitate prey tracking and capture by birds. Because the GDNs, which mediate escape initiation, are not sensitive to motion direction, we hypothesize that other neurons, in addition to the GDNs, are involved in influencing the direction of escape responses.     

A rare predator exploits prey escape behavior: the role of tail-fanning and plumage contrast in foraging of the painted redstart (Myioborus pictus)

Escape response, triggered by an approaching predator, is acommon antipredatory adaptation of arthropods against insectivores.The painted redstart, Myioborus pictus, represents insectivorousbirds that exploit such antipredatory behaviors by flushing,chasing, and preying upon flushed arthropods. In field experimentsI showed that redstarts evoke jump and flight in prey by spreadingwings and tail: this display increased frequency of aerial chasesby redstarts. Artificial models with spread tails also elicitedescape responses more often than models with closed tails and wings.The white patches on black wings and tails additionally help:the frequency of chases decreased when the white patches werecovered with black dye. Black models also tended to elicit escaperesponse less often than black-and-white models did, at leastin some situations. Hence, the prey's ability to detect birdsand to flee could cause the evolution of predators specializedat using conspicuous behavior and contrast in body colorationto elicit and exploit such antipredatory responses. Redstartsconstitute only a small proportion of the predatory guild, andtheir adaptations to exploit the prey's behavior illustratethe theoretically modeled "rare enemy" effect present in multispeciespredator-prey systems. This is the first experimental studyof morphological and behavioral adaptations of a rare predatorthat both elicits and exploits antipredator escape behaviorof its prey against more common predators. Hence, the studydocuments a behavior that could be evolutionarily explainedonly if indirect interactions in predator-prey communities aretaken into account.     

Habitat-specific sensory-exploitative signals in birds: propensity of dipteran prey to cause evolution of plumage variation in flush-pursuit insectivores

Sensory exploitation occurs when signals trigger behavioral reactions that diminish the receiver's fitness. Research in this area focuses on the match between the signal's form and the receiver's sensitivity, but the effect of habitat on interspecific sensory exploitation is rarely addressed. Myioborus redstarts use conspicuous wing and tail displays of contrasting black-and-white plumage patches to flush dipteran insects, which are then pursued and captured in flight. Previous studies have shown that by increasing the distance at which insects perform an escape response, conspicuous visual displays improve the birds' foraging performance. We tested the hypothesis that selection for a visual signal that maximizes prey escape distance under local habitat conditions can lead to the evolution of geographic variation in plumage pattern among Myioborus redstarts. Using models of foraging birds, we recorded the escape responses of Dipterous insects to a range of plumage patterns and background tones (from light to dark) to determine whether the plumage pattern that maximizes prey flushing is dependent upon that habitat (background) against which birds are viewed by their prey. Our results indicate that the effectiveness of a particular plumage pattern in flushing dipteran prey depends strongly on the background against which that plumage pattern is displayed, and darker habitat (background) conditions generally favor plumages with more extensive patches of white in the tail. However, the addition of white wing patches that imitate the plumage of the painted redstart (Myioborus pictus) generally increases insect escape responses but reduces the effect that tail pattern variation and background tone have on escape behavior. These experiments support the hypothesis that habitat-specific natural selection to enhance sensory exploitation of prey escape responses could produce geographic variation in plumage patterns of flush-pursuers.     

Tail flicking in the black redstart (<Emphasis Type="Italic">Phoenicurus ochruros</Emphasis>) and distance to cover

Tail flicking is a common behavior in many bird species, but its function is often unknown. Apart from intraspecific communication, tail flicking could be used during predator–prey communication, e.g., as a signal of prey vigilance or quality. We studied this behavior in the black redstart (Phoenicurus ochruros), a species that frequently shows tail flicking and is prone to attacks by ambushing predators that hide in cover. Hence, cover might be perceived as dangerous by this species. We hypothesized that flicking should increase with decreasing distance to cover. We counted the number of tail flicks of individuals and measured their distance to the nearest cover for an ambushing predator. We found that distance to cover had a significant effect on tail flicking behavior, as flicking increased with decreasing distance, but found no difference in flicking frequency between adults and juveniles or between sexes. Consequently, tail flicking is unlikely to signal submission or to be sexually selected in the black redstart. Since tail flicking also occurred in the absence of predators, we consider tail flicking in black redstarts to display vigilance and to be directed towards ambushing predators.     

Molecular diagnostics reveal spiders that exploit prey vibrational signals used in sexual communication

Vibrational signalling is a widespread form of animal communication and, in the form of sexual communication, has been generally regarded as inherently short‐range and a private communication channel, free from eavesdropping by generalist predators. A combination of fieldwork and laboratory experiments was used to test the hypothesis that predators can intercept and exploit such signals. First, we developed and characterized PCR primers specific for leafhoppers of the genus Aphrodes and specifically for the species Aphrodes makarovi. Spiders were collected from sites where leafhoppers were present and screened with these primers to establish which spider species were significant predators of this species during the mating period of these leafhoppers. Analysis using PCR of the gut contents of tangle‐web spiders, Enoplognatha ovata (Theridiidae), showed that they consume leafhoppers in the field at a greater rate when signalling adults were present than when nymphs were dominant, suggesting that the spiders were using these vibrations signals to find their prey. Playback and microcosm experiments then showed that E. ovata can use the vibrational signals of male leafhoppers as a cue during foraging and, as a result, killed significantly more male than female A. makarovi. Our results show, for the first time, that arthropod predators can exploit prey vibrational communication to obtain information about prey availability and use this information to locate and capture prey. This may be a widespread mechanism for prey location, one that is likely to be a major unrecognized driver of evolution in both predators and prey.     

Signalling conflict between prey and predator attraction

Predators may utilize signals to exploit the sensory biases of their prey or their predators. The inclusion of conspicuous silk structures called decorations or stabilimenta in the webs of some orb‐web spiders (Araneae: Araneidae, Tetragnathidae, Uloboridae) appears to be an example of a sensory exploitation system. The function of these structures is controversial but they may signal to attract prey and/or deter predators. Here, we test these predictions, using a combination of field manipulations and laboratory experiments. In the field, decorations influenced the foraging success of adult female St. Andrew’s Cross spiders, Argiope keyserlingi: inclusion of decorations increased prey capture rates as the available prey also increased. In contrast, when decorations were removed, prey capture rates were low and unrelated to the amount of available prey. Laboratory choice experiments showed that significantly more flies (Chrysomya varipes; Diptera: Calliphoridae) were attracted to decorated webs. However, decorations also attracted predators (adult and juvenile praying mantids, Archimantis latistylus; Mantodea: Mantidae) to the web. St. Andrew’s Cross spiders apparently resolve the conflicting nature of a prey‐ and predator‐attracting signal by varying their decorating behaviour according to the risk of predation: spiders spun fewer decorations if their webs were located in dense vegetation where predators had greater access, than if the webs were located in sparse vegetation.     

Lack of prey switching and strong preference for mosquito prey by a temporary pond specialist predator

1. The strengths of trophic interactions within ecosystems can be mediated by complex mechanisms that require elucidation if researchers are to understand and predict population- and community-level stabilities. Where multiple prey types co-occur, prey switching (i.e. frequency-dependent predation) by predators may facilitate low-density prey refuge effects which promote coexistence. On the other hand, lack of switching and strong preferences by predators can strongly suppress prey populations, which is especially important considering vector species such as mosquitoes. 2. The present study quantifies prey switching and preference patterns of the temporary pond specialist copepod Lovenula raynerae towards larvae of the medically important Culex pipiens mosquito complex in the presence of different proportions of alternative Daphnia pulex prey. Further, it examines whether prey switching and preferences are contingent on the sex of the predator. 3. Lovenula raynerae exhibited a lack of prey switching and strong preference for larval mosquito prey overall, irrespective of predator sex. Also, when larval mosquitoes were available in higher proportions over daphniids, the strength of this positive selectivity increased. There was very little low-density refuge for mosquitoes where they were rare. 4. Lack of prey switching and strong preferences towards mosquitoes by predatory paradiaptomid copepods may enhance population-level regulation of disease vector mosquitoes that exploit temporary pond-style habitats. Accordingly, the conservation and promotion of these predators might enable better management of medically important species across landscapes.     

Evolutionary significance of geographic variation in a plumage-based foraging adaptation: an experimental test in the slate-throated redstart (Myioborus miniatus)

Geographic variation in the plumage pattern of birds is widespread but poorly understood, and in very few cases has its evolutionary significance been investigated experimentally. Neotropical warblers of the genus Myioborus use their contrasting black-and-white plumage to flush insect prey during animated foraging displays. Although previous experimental work has demonstrated that white plumage patches are critical to flush-pursuit foraging success, the amount of white in the plumage shows considerable interspecific and intraspecific geographic variation. We investigated the evolutionary significance of this geographic variation by experimentally decreasing or increasing the amount of white in the tail of slate-throated redstarts (Myioborus miniatus comptus) from Monteverde, Costa Rica, to mimic the natural extremes of tail pattern variation in this species. In addition to measuring the effects of plumage manipulation on foraging performance, we performed field experiments measuring the escape response of a common insect prey species (an asilid fly) using model redstarts representing four different Myioborus plumage patterns. Our experiments were designed to test four hypotheses that could explain geographic variation in plumage pattern. Compared to controls, experimental birds with reduced-white tails that mimic the plumage pattern of M. miniatus hellmayri of Guatemala showed significant reductions in flush-pursuit foraging performance. In contrast, the addition of white to the tail to mimic the plumage pattern of M. miniatus verticalis of Bolivia had no significant effect on foraging performance of Costa Rican redstarts. In field experiments with asilid flies, model redstarts simulating the plumage of M. miniatus comptus of Costa Rica and M. miniatus verticalis of Bolivia elicited greater responses than did models of other Myioborus taxa with either less or more white in the plumage. The results of our experiments with both birds and insects allow us to reject two hypotheses for geographic variation in plumage pattern: (1) that geographic variation is a nonadaptive result of genetic drift, and (2) that selection for enhanced flush-pursuit foraging performance generally favors increased white in the plumage, but evolutionary trade-offs constrain the evolution of extensive patches of white in some geographic regions. Instead, our results suggest that geographic variation in the plumage pattern of Myioborus redstarts reflects adaptation to regional habitat characteristics that enhances flush-pursuit foraging performance.     

Revealing the role of predator interference in a predator–prey system with disease in prey population

Predation on a species subjected to an infectious disease can affect both the infection level and the population dynamics. There is an ongoing debate about the act of managing disease in natural populations through predation. Recent theoretical and empirical evidence shows that predation on infected populations can have both positive and negative influences on disease in prey populations. Here, we present a predator–prey system where the prey population is subjected to an infectious disease to explore the impact of predator on disease dynamics. Specifically, we investigate how the interference among predators affects the dynamics and structure of the predator–prey community. We perform a detailed numerical bifurcation analysis and find an unusually large variety of complex dynamics, such as, bistability, torus and chaos, in the presence of predators. We show that, depending on the strength of interference among predators, predators enhance or control disease outbreaks and population persistence. Moreover, the presence of multistable regimes makes the system very sensitive to perturbations and facilitates a number of regime shifts. Since, the habitat structure and the choice of predators deeply influence the interference among predators, thus before applying predators to control disease in prey populations or applying predator control strategy for wildlife management, it is essential to carefully investigate how these predators interact with each other in that specific habitat; otherwise it may lead to ecological disaster.     

Frequency-dependent predation and maintenance of prey polymorphism

In positive frequency-dependent predation, predation risk of an individual prey correlates positively with the frequency of that prey type. In a number of small-scale experiments individual predators have shown frequency-dependent behaviour, often leading to the conclusion that a population of such predators could maintain prey polymorphism. Using simulations, I studied the dynamics of frequency-dependent predation and prey polymorphism. The model suggests that persistence of prey polymorphism decreases with increasing number of predators that show frequency-dependent behaviour, questioning conclusions about polymorphism based on experiments with few predators. In addition, prey population size, prey crypsis, difference in crypsis between prey morphs and the way the behaviour was adjusted affected the persistence of polymorphism. Under some circumstances prey population remained polymorphic for a shorter time under frequency-dependent than under frequency-independent predation. This suggests that although positive frequency-dependent predator behaviour may maintain prey polymorphism, it is not a sufficient condition for persistent prey polymorphism.     

Exploitation of asymmetric predator–prey interactions by trophically transmitted parasites

The directionality of asymmetric interactions between predators (definitive hosts) and prey (intermediate hosts) should impact trophic transmission in parasites. This study tests the prediction that trophically transmitted parasites are funneled towards asymmetric predator–prey interactions where intermediate hosts have few predators and definitive hosts feed upon many prey (‘downward asymmetry’). The distribution of trophically transmitted parasites was examined in four published food webs in relation to mismatch asymmetry of predator–prey interactions. We found that trophically transmitted parasites exploit downwardly asymmetric interactions in a nonrandom manner, and particular predator–prey pairs contain more trophically transmitted parasites than would be expected by random chance alone. These findings suggest that food web topology has great bearing on the ecology of trophically transmitted parasites, and that consideration of parasite life cycles in the context of food web organization can provide insights into the forces affecting the evolution of trophic transmission.     

The effect of habitat structure on prey mortality depends on predator and prey microhabitat use

Structurally complex habitats provide cover and may hinder the movement of animals. In predator–prey relationships, habitat structure can decrease predation risk when it provides refuges for prey or hinders foraging activity of predators. However, it may also provide shelter, supporting structures and perches for sit-and-wait predators and hence increase their predation rates. We tested the effect of habitat structure on prey mortality in aquatic invertebrates in short-term laboratory predation trials that differed in the presence or absence of artificial vegetation. The effect of habitat structure on prey mortality was context dependent as it changed with predator and prey microhabitat use. Specifically, we observed an ‘anti-refuge’ effect of added vegetation: phytophilous predators that perched on the plants imposed higher predation pressure on planktonic prey, while mortality of benthic prey decreased. Predation by benthic and planktonic predators on either type of prey remained unaffected by the presence of vegetation. Our results show that the effects of habitat structure on predator–prey interactions are more complex than simply providing prey refuges or cover for predators. Such context-specific effects of habitat complexity may alter the coupling of different parts of the ecosystem, such as pelagic and benthic habitats, and ultimately affect food web stability through cascading effects on individual life histories and trophic link strengths.     

Predators target rare prey in coral reef fish assemblages

Predation can result in differing patterns of local prey diversity depending on whether predators are selective and, if so, how they select prey. A recent study comparing the diversity of juvenile fish assemblages among coral reefs with and without predators concluded that decreased prey diversity in the presence of predators was most likely caused by predators actively selecting rare prey species. We used several related laboratory experiments to explore this hypothesis by testing: (1) whether predators prefer particular prey species, (2) whether individual predators consistently select the same prey species, (3) whether predators target rare prey, and (4) whether rare prey are more vulnerable to predation because they differ in appearance/colouration from common prey. Rare prey suffered greater predation than expected and were not more vulnerable to predators because their appearance/colouration differed from common prey. Individual predators did not consistently select the same prey species through time, suggesting that prey selection behaviour was flexible and context dependent rather than fixed. Thus, selection of rare prey was unlikely to be explained by simple preferences for particular prey species. We hypothesize that when faced with multiple prey species predators may initially focus on rare, conspicuous species to overcome the sensory confusion experienced when attacking aggregated prey, thereby minimizing the time required to capture prey. This hypothesis represents a community-level manifestation of two well-documented and related phenomena, the “confusion effect” and the “oddity effect”, and may be an important, and often overlooked, mechanism by which predators influence local species diversity.     

Encounter success of free-ranging marine predator movements across a dynamic prey landscape

Movements of wide-ranging top predators can now be studied effectively using satellite and archival telemetry. However, the motivations underlying movements remain difficult to determine because trajectories are seldom related to key biological gradients, such as changing prey distributions. Here, we use a dynamic prey landscape of zooplankton biomass in the north-east Atlantic Ocean to examine active habitat selection in the plankton-feeding basking shark Cetorhinus maximus. The relative success of shark searches across this landscape was examined by comparing prey biomass encountered by sharks with encounters by random-walk simulations of 'model' sharks. Movements of transmitter-tagged sharks monitored for 964 days (16754 km estimated minimum distance) were concentrated on the European continental shelf in areas characterized by high seasonal productivity and complex prey distributions. We show movements by adult and sub-adult sharks yielded consistently higher prey encounter rates than 90% of random-walk simulations. Behavioural patterns were consistent with basking sharks using search tactics structured across multiple scales to exploit the richest prey areas available in preferred habitats. Simple behavioural rules based on learned responses to previously encountered prey distributions may explain the high performances. This study highlights how dynamic prey landscapes enable active habitat selection in large predators to be investigated from a trophic perspective, an approach that may inform conservation by identifying critical habitat of vulnerable species.     

Competition and stoichiometry: coexistence of two predators on one prey

The competitive exclusion principle (CEP) states that no equilibrium is possible if n species exploit fewer than n resources. This principle does not appear to hold in nature, where high biodiversity is commonly observed, even in seemingly homogenous habitats. Although various mechanisms, such as spatial heterogeneity or chaotic fluctuations, have been proposed to explain this coexistence, none of them invalidates this principle. Here we evaluate whether principles of ecological stoichiometry can contribute to the stable maintenance of biodiverse communities. Stoichiometric analysis recognizes that each organism is a mixture of multiple chemical elements such as carbon (C), nitrogen (N), and phosphorus (P) that are present in various proportions in organisms. We incorporate these principles into a standard predator-prey model to analyze competition between two predators on one autotrophic prey. The model tracks two essential elements, C and P, in each species. We show that a stable equilibrium is possible with two predators on this single prey. At this equilibrium both predators can be limited by the P content of the prey. The analysis suggests that chemical heterogeneity within and among species provides new mechanisms that can support species coexistence and that may be important in maintaining biodiversity.     

Diet of intraguild predators affects antipredator behavior in intraguild prey

In two-predator, one-prey systems with intraguild predationand patchily distributed prey, the intraguild prey may facea choice between prey patches with and without intraguild predators.To minimize falling victim to intraguild predation, intraguildprey are expected to perceive cues specifically associated withthe presence of intraguild predators. We investigate whetherintraguild prey avoided intraguild predators and which cuestriggered this behavior in a system composed of plant-inhabitingarthropods. We found that intraguild prey recognized intraguildpredators from a distance, based on their diet: they avoidedodors of intraguild predators that had consumed shared preybut did not avoid odors of intraguild predators that had fedon other diets, including a diet of conspecifics. When intraguildprey were foraging on a patch, detection of intraguild predatorsled to longer periods of immobility and to fewer captures ofthe shared prey. However, intraguild predators that were eitherstarved or had previously consumed intraguild prey posed a higherrisk to intraguild prey than did intraguild predators that hadconsumed the shared prey. We conclude that the cues used byintraguild prey to avoid intraguild predators are associatedwith the circumstances under which they encounter intraguildpredators in the field and not to different degrees of danger.     

Intraspecific variation in prey quality: a comparison of nutrient presence in prey and nutrient extraction by predators

Prey quality can have large impacts on the survival, growth and behavior of predators. A number of studies have examined how different species of prey vary in quality. However, far less is known about intraspecific variation in the quality of prey for predators and even less about what nutrients are extracted from prey by predators. We examined how the sex, feeding level and developmental status of prey affected the quantities of nutrients present in prey bodies and the quantities of nutrients that could be extracted from prey by spiders. Female and well‐fed prey were larger and had more nutrients than male and food‐limited prey, respectively. After taking into account differences in prey size, spiders extracted relatively more lipid and less protein from female and well‐fed prey than from male and food‐limited prey, respectively. Mealworms were of higher quality than adult mealworm beetles; spiders were able to extract more lipid, protein and other nutrients from larvae than adults. While lipid present in prey was a good predictor of lipid consumed, protein present in prey was not a reliable predictor of protein consumed. The variation in prey quality that we observed within a single species of prey (i.e. well‐fed vs food‐limited crickets) was as large as variation in quality among the three species of prey used in these experiments. Intraspecific variation in prey quality may be an important factor affecting predatory arthropods, especially in habitats or at times of year when one species of prey is abundant. Further studies are needed to examine the consequences of intraspecific variation in prey quality on the life history and behavior of predators.     

Effects of successive predator attacks on prey aggregations

We study the cumulative effect of successive predator attacks on the disturbance of a prey aggregation using a modelling approach. Our model intends to represent fish schools attacked by both aerial and underwater predators. This individual-based model uses long-distance attraction and short-distance repulsion between prey, which leads to prey aggregation and swarming in the absence of predators. When intermediate-distance alignment is added to the model, the prey aggregation displays a cohesive displacement, i.e., schooling, instead of swarming. Including predators, i.e. with repulsion behaviour for prey to predators in the model, leads to flash expansion of the prey aggregation after a predator attack. When several predators attack successively, the prey aggregation dynamics is a succession of expanding-grouping-swarming/schooling phases. We quantify this dynamics by recording the changes in the simulated prey aggregation radius over time. This radius is computed as the longest distance of individual prey to the aggregation centroid, and it is assumed to increase along with prey disturbance. The prey aggregation radius generally increases during flash expansion, then decreases during grouping until reaching a constant lowest level during swarming/schooling. This general dynamics is modulated by several parameters: the frequency, direction (vertical vs. horizontal) and target (centroid of the prey aggregation vs. random prey) of predator attacks; the distance at which prey detect predators; the number of prey and predators. Our results suggest that both aerial and underwater predators are more efficient at disturbing fish schools by increasing their attack frequency at such level that the fish cannot return to swarming/schooling. We find that a mix between aerial and underwater predators is more efficient at disturbing a fish school than a single type of attack, suggesting that aerial and underwater foragers may gain mutual benefits in forming foraging groups.     

Predator impacts on stream benthic prey

The impact that predators have on benthic, macroinvertebrate prey density in streams is unclear. While some studies show a strong effect of predators on prey density, others show little or no effect. Two factors appear to influence the detection of predator impact on prey density in streams. First, many field studies have small sample sizes and thus might be unable to detect treatment effects. Second, streams contain two broad classes of predators, invertebrates and vertebrates, which might have different impacts on prey density for a variety of reasons, including availability of refuge for prey and prey emigration responses to the two types of predators. In addition, predatory vertebrates have more complex prey communities than predatory invertebrates; this complexity might reduce the impact that predatory vertebrates have on prey because of indirect effects. I conducted a meta-analysis on the results of field studies that manipulate predator density in enclosures to determine (1) if predators have a significant impact on benthic prey density in streams, (2) if the impacts that predatory invertebrates and vertebrates have differ, and (3) if predatory vertebrates have different impacts on predatory prey versus herbivorous prey. The results of the meta-analysis suggest that on average predators have a significant negative effect on prey density, predatory invertebrates have a significantly stronger impact than predatory vertebrates, and predatory vertebrates do not differ in their impact on predatory versus herbivorous invertebrate prey. Three methodological variables (mesh size of enclosures, size of enclosures, and experimental duration) were examined to determine if cross correlations exist that may explain the differences in impact between predatory invertebrates and vertebrates. No correlation exists between mesh size and predator impact. Over all predators, no correlation exists between experimental duration and predator impact; however, within predatory invertebrates a correlation does exist between these variables. Also, a correlation was found between enclosure size and predator impact. This correlation potentially explains the difference in impact between predatory invertebrates and predatory vertebrates. Results of the meta-analysis suggest two important areas for future research: (1) manipulate both types of predators within the same system, and (2) examine their impacts on the same spatial scale.     

Foraging activity of a dominant epigeal predator: molecular evidence for the effect of prey density on consumption

Despite the widely held assumption that ‘generalist’ predators consume most prey available to them, there is a growing body of evidence suggesting otherwise. Generalists are expected to perform well in disturbed areas because they can switch between prey pathways when one food source becomes depleted. Indeed, these predators have the potential to promote diversity by switching to prey in a frequency dependent manner and consume prey groups in relation to local abundance. It is therefore important to understand how predation rates fluctuate as local availability changes. We performed open‐field and mesocosm experiments in a corn and soybean agroecosystem to delineate the role prey density plays in determining predation frequency of a dominant epigeal predator. To track trophic pathways, molecular gut‐content analysis using enzyme‐linked immunosorbent assay (ELISA) was performed to track foraging behavior of the wolf spider Pardosa milvina feeding on dipterans, flies. Extensive monitoring of foraging activity and prey populations revealed that predation varied temporally. Importantly, the frequency of individuals testing positive for flies was lower than predicted when flies were extremely abundant but higher when they were scarce, relative to the prey community as a whole. Furthermore, isolating predators in mesocosms revealed an effect of Diptera density on the likelihood of consumption, as determined by ELISA, only when flies were at low levels (12.5% of prey provided). The molecular results suggest that these spiders do not appear to be consuming flies in a frequency‐dependent manner where the decision to switch between different prey pathways is driven by relative abundance. Rather, selectivity of prey is somewhat independent of variation of other prey groups, which is indicative of their consistent reliance on dipterans and may be related to nutritional requirements and/or capture success.