Prey Mortality Research Articles

Human hunting and site occupation intensity in the Early Epipaleolithic of the Jordanian western highlands

We investigate the effects of the Last Glacial Maximum (∼25,000–18,500 cal BP) on human hunting and settlement strategies through the study of faunal remains from four Early Epipaleolithic sites located in the western highlands region of Jordan. Human mobility is monitored by reconstructing site occupation intensity using zooarchaeological measures of dietary breadth and prey mortality. Our data reveal light occupation and a mobile human adaptation focused on the hunting of high-ranked adult ungulates and large-bodied tortoises. Despite their mobile strategy, the Early Epipaleolithic inhabitants clearly preferred particular locations on the landscape and reoccupied them repeatedly over time.

Native prey mortality increases but remains density-dependent following lionfish invasion

Native prey mortality increases but remains density-dependent following lionfish invasion

Density-dependent prey mortality is determined by the spatial scale of predator foraging

Foraging theory predicts which prey patches predators should target. However, in most habitats, what constitutes a 'patch' and how prey density is calculated are subjective concepts and depend on the spatial scale at which the predator (or scientist) is observing. Moreover, the predator's 'foraging scale' affects prey population dynamics: predators should produce directly density-dependent (DDD) prey mortality at the foraging scale, but inversely density-dependent (IDD) mortality (safety-in-numbers) at smaller scales. We performed the first experimental test of these predictions using behavioral assays with guppies (Poecilia reticulata) feeding on bloodworm 'prey' patches. The guppy's foraging scale had already been estimated in a prior study. Our experimental results confirmed theoretical predictions: predation was IDD when prey were aggregated at a scale smaller than the foraging scale, but not when prey were aggregated at larger scales. These results could be used to predict outcomes of predator-prey interactions in continuous, non-discrete habitats in the field.

Body size affects the evolution of eyespots in caterpillars

Many caterpillars have conspicuous eye-like markings, called eyespots. Despite recent work demonstrating the efficacy of eyespots in deterring predator attack, a fundamental question remains: Given their protective benefits, why have eyespots not evolved in more caterpillars? Using a phylogenetically controlled analysis of hawkmoth caterpillars, we show that eyespots are associated with large body size. This relationship could arise because (i) large prey are innately conspicuous; (ii) large prey are more profitable, and thus face stronger selection to evolve such defenses; and/or (iii) eyespots are more effective on large-bodied prey. To evaluate these hypotheses, we exposed small and large caterpillar models with and without eyespots in a 2 × 2 factorial design to avian predators in the field. Overall, eyespots increased prey mortality, but the effect was particularly marked in small prey, and eyespots decreased mortality of large prey in some microhabitats. We then exposed artificial prey to naïve domestic chicks in a laboratory setting following a 2 × 3 design (small or large size × no, small, or large eyespots). Predators attacked small prey with eyespots more quickly, but were more wary of large caterpillars with large eyespots than those without eyespots or with small eyespots. Taken together, these data suggest that eyespots are effective deterrents only when both prey and eyespots are large, and that innate aversion toward eyespots is conditional. We conclude that the distribution of eyespots in nature likely results from selection against eyespots in small caterpillars and selection for eyespots in large caterpillars (at least in some microhabitats).

Intraguild Predation in Heteroptera: Effects of Density and Predator Identity on Dipteran Prey.

In tropical freshwaters, different species of water bugs (Heteroptera) constitute a guild sharing similar prey resources including chironomid and mosquito larvae. Assuming possibilities of intraguild predation (IGP) among the constituent members, an attempt was made to evaluate the effects of prey and predator density on the mortality of mosquito and chironomid larvae (shared prey), using Laccotrephes griseus Guérin-Méneville (Hemiptera: Nepidae) and Ranatra filiformis Fabricius (Hemiptera: Nepidae) as IG predators and Anisops bouvieri Kirkaldy (Hemiptera: Notonectidae) as IG prey. The predation on mosquito and chironomid larvae varied with the density and combinations of the predators. When present as conspecific IG predators, L. griseus exhibited greater effect on the prey mortality than R. filiformis. The effects on shared prey suggest that the two predators are not substitutable in terms of the effect on the shared prey mortality. The mortality of A. bouvieri (IG prey) at low shared prey density was significantly different (p < 0.05) from high shared prey density. In view of predatory effect of the heteropteran predators on the dipteran larvae, the results suggest possible interference by the presence of A. bouvieri as an intermediate predator. It seems that the presence of heteropteran predators including A. bouvieri as IG prey may benefit the dipteran prey under situations when the density is low in tropical waters. The intensity of the predatory effect may differ based on the species composition at IG predator level. For mosquito biological control, the interactions between the predators may not be substitutable and are independent in their effects.

Interactive effects of pesticide exposure and habitat structure on behavior and predation of a marine larval fish.

Coastal development has generated multiple stressors in marine and estuarine ecosystems, including habitat degradation and pollutant exposure, but the effects of these stressors on the ecology of fishes remain poorly understood. We studied the separate and combined effects of an acute 4h sublethal exposure of the pyrethroid pesticide esfenvalerate and structural habitat complexity on behavior and predation risk of larval topsmelt (Atherinops affinis). Larvae were exposed to four nominal esfenvalerate concentrations (control, 0.12, 0.59, 1.18μg/L), before placement into 12L mesocosms with a three-spine stickleback (Gasterosteus aculeatus) predator. Five treatments of artificial eelgrass included a (1) uniform and (2) patchy distribution of eelgrass at a low density (500shootsperm(2)), a (3) uniform and (4) patchy distribution of eelgrass at a high density (1,000shootsperm(2)), and (5) the absence of eelgrass. The capture success of predators and aggregative behavior of prey were observed in each mesocosm for 10min of each trial, and mortality of prey was recorded after 60min. Exposure to esfenvalerate increased the proportion of larvae with swimming abnormalities. Surprisingly, prey mortality did not increase linearly with pesticide exposure but increased with habitat structure (density of eelgrass), which may have been a consequence of compensating predator behavior. The degree of prey aggregation decreased with both habitat structure and pesticide exposure, suggesting that anti-predator behaviors by prey may have been hampered by the interactive effects of both of these factors.

Oyster reef restoration: effect of alternative substrates on oyster recruitment and nekton habitat use

Eastern oysters (Crassostrea virginica) in Gulf of Mexico estuaries create complex reefs and provide important habitat for fish and crustaceans. Oyster reefs have suffered historic losses due to overharvest, disease, and degraded water quality, and recent efforts have focused on restoring reefs to benefit nekton populations. Oyster shell is the preferred substrate for oyster reef restoration, but as a consequence of its limited supply, a variety of alternative substrates are being used. We used field experiments to quantify the effects of substrate type (concrete, porcelain, limestone, river rock, and oyster shell) on oyster recruitment, growth, and nekton habitat use in St. Charles Bay, TX. After 4 months, oyster spat recruitment density, nekton density and community structure were similar across substrate types—and analogous to those on natural reefs—but differed from samples collected on bare sediment. To determine refuge value of the alternative substrates, we tested mud crab (Panopeidae) prey mortality with and pinfish (Lagodon rhomboides) or blue crab (Callinectes sapidus) predators. Prey mortality was similar across substrate types for both predators, and was significantly lower than no substrate and bare sand controls. Alternative substrates can provide important structural materials to support the development of oyster populations and nekton assemblages, and may be used to promote sustainable management of oyster reef resources via restoration.

Trade‐offs between supportive and provisioning ecosystem services of forage species in marine food webs.

Ecosystem-based management of natural resources involves an explicit consideration of trade-offs among ecosystem services. In marine fisheries, there is the potential for a trade-off between the supporting role of small pelagic fish and cephalopods in food webs, and the provisioning service they play as a major target of fisheries. Because these species play central roles in food webs by providing a conduit of energy from small prey to upper trophic level predators, we hypothesized that trade-offs between these two ecosystem services could be predicted based on energetic properties of predator–prey linkages and food-web structure. We compiled information from 27 marine food-web models (all within the Ecopath framework) that included either small pelagic fish or cephalopods, described predator–prey linkages involving these species, and developed a novel analytical framework to estimate how changes in yields of forage species would propagate through food webs and other fisheries. Consistent with expectations, diet overlap between predators and prey was generally low, and predator–prey linkages tended to be asymmetric; contribution of these species to predator diets was, on average, larger than the contribution of individual predator stocks to prey mortality. The estimated trade-offs between yields of forage fish and predator species were highly variable when we assumed joint bottom-up and top-down control on predation. Roughly one-third of this variance was related to an interactive effect of fishing and predation intensity; strong trade-offs were predicted when fishing intensity on forage species is high and when predators account for a high proportion of total forage mortality. When trophic connections were presumed to be driven by bottom-up processes, trade-offs were more predictable, but generally very small. Contrary to our expectations, trade-offs were not easily predicted from energetic properties, largely because predators of forage species exhibited a high degree of intra-guild predation, and also consumed many of the same prey as forage species. Given the limited ability to a priori predict the food-web implications of forage fisheries, we suggest that a precautionary risk-based approach be applied to decisions about acceptable biological removals of forage fish and biological targets used for their management.

Feedback between size balance and consumption strongly affects the consequences of hatching phenology in size‐dependent predator–prey interactions

In many size‐dependent predator–prey systems, hatching phenology strongly affects predator–prey interaction outcomes. Early‐hatched predators can easily consume prey when they first interact because they encounter smaller prey. However, this process by itself may be insufficient to explain all predator–prey interaction outcomes over the whole interaction period because the predator–prey size balance changes dynamically throughout their ontogeny. We hypothesized that hatching phenology influences predator–prey interactions via a feedback mechanism between the predator–prey size balance and prey consumption by predators. We experimentally tested this hypothesis in an amphibian predator–prey model system. Frog tadpoles Rana pirica were exposed to a predatory salamander larva Hynobius retardatus that had hatched 5, 12, 19 or 26 days after the frog tadpoles hatched. We investigated how the salamander hatch timing affected the dynamics of prey mortality, size changes of both predator and prey, and their subsequent life history (larval period and size at metamorphosis). The predator–prey size balance favoured earlier hatched salamanders, which just after hatching could successfully consume more frog tadpoles than later hatched salamanders. The early‐hatched salamanders grew rapidly and their accelerated growth enabled them to maintain the predator‐superior size balance; thus, they continued to exert strong predation pressure on the frog tadpoles in the subsequent period. Furthermore, frog tadpoles exposed to the early‐hatched salamanders were larger at metamorphosis and had a longer larval period than other frog tadpoles. These results suggest that feedback between the predator‐superior size balance and prey consumption is a critical mechanism that strongly affects the impacts of early hatching of predators in the short‐term population dynamics and life history of the prey. Because consumption of large nutrient‐rich prey items supports the growth of predators, a similar feedback mechanism may be common and have strong impacts on phenological shifts in size‐dependent trophic relationships.

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.

Interactive prey and predator diversity effects drive consumption rates

The positive relationship between biodiversity and ecosystem functioning is mainly derived from studies concerning primary producers, whereas a generalization of this relationship for higher trophic levels is more difficult. Furthermore, most evidence of the biodiversity–ecosystem functioning relationship is derived from experiments manipulating only one trophic level and, as a consequence, interactive diversity effects at multiple trophic levels have mostly been ignored. Here, we performed a mesocosm experiment in which we manipulated functional group diversity at two trophic levels (primary and secondary consumers) applying a full‐factorial design. More specifically, we asked whether 1) predator functional diversity affects prey mortality rates, 2) prey functional diversity affects prey mortality rates, 3) whether there are interactive effects of simultaneous diversity changes at both trophic levels. For each trophic level we used two functional groups, i.e. organisms belonging to two different habitat domains: at the higher trophic position 1) a ground foraging spider species and 2) a spider species foraging in the vegetation canopy and at the lower trophic position 3) a ground living cricket species and 4) leafhoppers living in the vegetation canopy. Increasing predator functional group diversity increased prey mortality by 53%, and increasing prey functional group diversity increased prey mortality by 24%. Further, prey mortality was highest at the uppermost level of functional group diversity (142% increase in prey mortality compared to single prey and predator functional diversity), most likely due to resource partitioning between the predators. This finding demonstrates that a multi‐trophic perspective is necessary, and that previous studies focusing on only one trophic level have most likely underestimated the strength of the relationship between biodiversity and ecosystem functioning.

Influence of density on intraguild predation of aquatic Hemiptera (Heteroptera): implications in biological control of mosquito

The water bugs &lt;em&gt;Diplonychus rusticus&lt;/em&gt; (Fabricius) (Heteroptera: Belostomatidae) and &lt;em&gt;Anisops bouvieri&lt;/em&gt; (Kirkaldy) (Heteroptera: Notonectidae) co-occur in wetlands sharing mosquito larvae as prey. As a consequence, an asymmetrical intraguild predation (IGP) involving D. rusticus as IG predator and &lt;em&gt;A. bouvieri&lt;/em&gt; as IG prey can be possible, the outcome of which may vary with the relative density of interacting species. Based on this proposition density dependent effects on the IG prey and shared prey mortality were assessed in the laboratory using varying numbers of IG predator and shared prey (IV instar &lt;em&gt;Culex quinquefasciatus&lt;/em&gt; larva). In contrast to single predator system, mosquito larvae were proportionately less vulnerable to predation in IGP, at low density of shared prey. An increase in density of mosquito decreased the mortality of IG prey (&lt;em&gt;A. bouvieri&lt;/em&gt;), but the mean mortality of the IG prey increased with the density of IG predator, in IGP system. Increase in density of mosquito and &lt;em&gt;D. rusticus&lt;/em&gt; enhanced risk to predation of mosquito while reducing the mortality of &lt;em&gt;A. bouvieri&lt;/em&gt;. Interaction between &lt;em&gt;D.&lt;/em&gt; &lt;em&gt;rusticus&lt;/em&gt; and &lt;em&gt;A. bouvieri&lt;/em&gt; as a part of IGP system provides a possible reason of coexistence of mosquito immature along with predators in wetlands. Biological regulation of mosquitoes may be affected, if appropriate predator numbers are not available in the habitats.

Nile perch (Lates niloticus, L.) and cichlids (Haplochromis spp.) in Lake Victoria: could prey mortality promote invasion of its predator?

The invasion of Nile perch into Lake Victoria is one of the iconic examples of the destructive effect of an introduced species on an ecosystem but no convincing explanation exists of why Nile perch only increased dramatically after a 25 year lag. Here, we consider this problem using a mathematical model that takes into account interactions between Nile perch and its cichlid prey. We examined competing hypotheses to explain Nile perch invasion and show that suppression of juvenile Nile perch by cichlids may cause the system to have two alternative stable states: one with only cichlids and one with coexistence of cichlids and Nile perch. Without cichlid predation on Nile perch, alternative stable states did not occur. Our analysis indicates that cichlid mortality, for example fishing mortality, may have induced the observed shift between the states.

African Vultures Don’t Follow Migratory Herds: Scavenger Habitat Use Is Not Mediated by Prey Abundance

The ongoing global decline in vulture populations raises major conservation concerns, but little is known about the factors that mediate scavenger habitat use, in particular the importance of abundance of live prey versus prey mortality. We test this using data from the Serengeti-Mara ecosystem in East Africa. The two hypotheses that prey abundance or prey mortality are the main drivers of vulture habitat use provide alternative predictions. If vultures select areas based only on prey abundance, we expect tracked vultures to remain close to herds of migratory wildebeest regardless of season. However, if vultures select areas where mortality rates are greatest then we expect vultures to select the driest regions, where animals are more likely to die of starvation, and to be attracted to migratory wildebeest only during the dry season when wildebeest mortality is greatest. We used data from GSM-GPS transmitters to assess the relationship between three vulture species and migratory wildebeest in the Mara-Serengeti ecosystem. Results indicate that vultures preferentially cluster around migratory herds only during the dry season, when herds experience their highest mortality. Additionally during the wet season, Ruppell’s and Lappet-faced vultures select relatively dry areas, based on Normalized Difference Vegetation Index, whereas White-backed vultures preferred wetter areas during the wet season. Differences in habitat use among species may mediate coexistence in this scavenger guild. In general, our results suggest that prey abundance is not the primary driver of avian scavenger habitat use. The apparent reliance of vultures on non-migratory ungulates during the wet season has important conservation implications for vultures in light of on-going declines in non-migratory ungulate species and use of poisons in unprotected areas.

Mosquito Prey Vulnerability in Intraguild Predation Between Ranatra filiformis and Anisops bouvieri: Implications in Biological Control

Wetlands are common habitats of a range of predatory water bugs (Heteroptera) constituting a guild that exhibit similar dietary choice including mosquito. Differences in body size and micro habitat preference among the heteropteran guild members provide a fair possibility of intraguild predation that can influence the regulatory effect on the prey species. This proposition was tested under laboratory conditions, using varying density of Ranatra filiformis (IG predator) and Anisops bouvieri (IG prey) as predators against mosquito larvae as shared prey. Compared to single predator system, mosquito larvae were proportionately less vulnerable to predation in intraguild predation (IGP), at low density of shared prey. In IGP system, vulnerability of shared prey increased with increase in density accompanied by a decline in mortality of IG prey. The mean mortality of shared prey and IG prey increased with the density of IG predator. It was apparent that the mosquito prey vulnerability was enhanced with increase in density of mosquito and R. filiformis while reducing the mortality of A. bouvieri partly. The interaction between R. filiformis and A. bouvieri as a part of IGP system indicate about the possible mechanism of coexistence of predators and prey in the wetlands. The density dependent effects on reduction and enhancement of shared prey (mosquito) mortality indicate that appropriate ratio of R. filiformis, A. bouvieri and mosquito larvae will be required to make biological regulation of wetland mosquitoes feasible.

Prey mortality profiles indicate that Early Pleistocene Homo at Olduvai was an ambush predator

The prime-adult-dominated mortality profile of large bovids in the 1.8 Ma FLK Zinj assemblage, Olduvai Gorge, Tanzania, was recently attributed to ambush hunting by early Homo (Bunn, H.T., Pickering, T.R. 2010. Quat. Res. 74, 395–404). We now investigate a logical follow-up question: is enough known about the causes and pervasiveness of prime-adult-dominated mortality profiles (defined as >70% prime adults) from modern ecosystems and from archaeological sites to warrant their attribution solely to hominin hunting? Besides hominin hunting, three methods of scavenging could have provided the large bovids butchered at FLK Zinj: first-access scavenging from non-predator-related accidents; late-access passive scavenging from lion (or other) kills; early-access aggressive scavenging from lion (or other) kills.We present new data on hunted prey from Hadza bow hunting (e.g., N = 50 impala; N = 18 greater kudu) near Lake Eyasi, Tanzania, and from San bow hunting (N = 13 gemsbok) in the Kalahari Desert, Botswana, documenting non-selective, living-structure profiles. We present new data on drowned wildebeest (N = 175) from Lake Masek, in the Serengeti, documenting many prime adults but also a significantly high percentage of old adults, unlike the profile at FLK Zinj. We also examine mortality profiles from modern African lions and from Old World Pleistocene archaeological sites, revealing that while prime-dominated profiles are present in some archaeological assemblages, particularly some Late Pleistocene European sites involving cervids, they are not documented from lion or other larger carnivore predation; moreover, living-structure profiles with prime adults representing ∼50–60% of prey are common, particularly in African archaeological assemblages involving bovids hunted by humans. Although taphonomic bias, prey socioecology, and season of death may all influence mortality profiles, prime-dominated profiles require careful evaluation. The prime-dominated profile at FLK Zinj is significantly different from profiles formed by the three scavenging methods, which likely indicates hunting by Early Pleistocene Homo.

NONCONSUMPTIVE PREDATOR-DRIVEN MORTALITY CAUSES NATURAL SELECTION ON PREY

Predators frequently exert natural selection through differential consumption of their prey. However, predators may also cause prey mortality through nonconsumptive effects, which could cause selection if different prey phenotypes are differentially susceptible to this nonconsumptive mortality. Here we present an experimental test of this hypothesis, which reveals that nonconsumptive mortality imposed by predatory dragonflies causes selection on their damselfly prey favoring increased activity levels. These results are consistent with other studies of predator-driven selection, however, they reveal that consumption alone is not the only mechanism by which predators can exert selection on prey. Uncovering this mechanism also suggests that prey defensive traits may represent adaptations to not only avoid being consumed, but also for dealing with other sources of mortality caused by predators. Demonstrating selection through both consumptive and nonconsumptive predator mortality provides us with insight into the diverse effects of predators as an evolutionary force.

Predator density and the functional responses of coral reef fish

Predation is a key process driving coral reef fish population dynamics, with higher per capita prey mortality rates on reefs with more predators. Reef predators often forage together, and at high densities, they may either cooperate or antagonize one another, thereby causing prey mortality rates to be substantially higher or lower than one would expect if predators did not interact. However, we have a limited mechanistic understanding of how prey mortality rates change with predator densities. We re-analyzed a previously published observational dataset to investigate how the foraging response of the coney grouper (Cephalopholis fulva) feeding on the bluehead wrasse (Thalassoma bifasciatum) changed with shifts in predator and prey densities. Using a model-selection approach, we found that per-predator feeding rates were most consistent with a functional response that declines as predator density increases, suggesting either antagonistic interactions among predators or a shared antipredator behavioral response by the prey. Our findings suggest that variation in predator density (natural or anthropogenic) may have substantial consequences for coral reef fish population dynamics.

Fear on the move: predator hunting mode predicts variation in prey mortality and plasticity in prey spatial response

Ecologists have long searched for a framework of a priori species traits to help predict predator-prey interactions in food webs. Empirical evidence has shown that predator hunting mode and predator and prey habitat domain are useful traits for explaining predator-prey interactions. Yet, individual experiments have yet to replicate predator hunting mode, calling into question whether predator impacts can be attributed to hunting mode or merely species identity. We tested the effects of spider predators with sit-and-wait, sit-and-pursue and active hunting modes on grasshopper habitat domain, activity and mortality in a grassland system. We replicated hunting mode by testing two spider predator species of each hunting mode on the same grasshopper prey species. We observed grasshoppers with and without each spider species in behavioural cages and measured their mortality rates, movements and habitat domains. We likewise measured the movements and habitat domains of spiders to characterize hunting modes. We found that predator hunting mode explained grasshopper mortality and spider and grasshopper movement activity and habitat domain size. Sit-and-wait spider predators covered small distances over a narrow domain space and killed fewer grasshoppers than sit-and-pursue and active predators, which ranged farther distances across broader domains and killed more grasshoppers, respectively. Prey adjusted their activity levels and horizontal habitat domains in response to predator presence and hunting mode: sedentary sit-and-wait predators with narrow domains caused grasshoppers to reduce activity in the same-sized domain space; more mobile sit-and-pursue predators with broader domains caused prey to reduce their activity within a contracted horizontal (but not vertical) domain space; and highly mobile active spiders led grasshoppers to increase their activity across the same domain area. All predators impacted prey activity, and sit-and-pursue predators generated strong effects on domain size. This study demonstrates the validity of utilizing hunting mode and habitat domain for predicting predator-prey interactions. Results also highlight the importance of accounting for flexibility in prey movement ranges as an anti-predator response rather than treating the domain as a static attribute.

Nonconsumptive effects in a multiple predator system reduce the foraging efficiency of a keystone predator.

Many studies have demonstrated that the nonconsumptive effect (NCE) of predators on prey traits can alter prey demographics in ways that are just as strong as the consumptive effect (CE) of predators. Less well studied, however, is how the CE and NCE of multiple predator species can interact to influence the combined effect of multiple predators on prey mortality. We examined the extent to which the NCE of one predator altered the CE of another predator on a shared prey and evaluated whether we can better predict the combined impact of multiple predators on prey when accounting for this influence. We conducted a set of experiments with larval dragonflies, adult newts (a known keystone predator), and their tadpole prey. We quantified the CE and NCE of each predator, the extent to which NCEs from one predator alters the CE of the second predator, and the combined effect of both predators on prey mortality. We then compared the combined effect of both predators on prey mortality to four predictive models. Dragonflies caused more tadpoles to hide under leaf litter (a NCE), where newts spend less time foraging, which reduced the foraging success (CE) of newts. Newts altered tadpole behavior but not in a way that altered the foraging success of dragonflies. Our study suggests that we can better predict the combined effect of multiple predators on prey when we incorporate the influence of interactions between the CE and NCE of multiple predators into a predictive model. In our case, the threat of predation to prey by one predator reduced the foraging efficiency of a keystone predator. Consequently, the ability of a predator to fill a keystone role could be compromised by the presence of other predators.