Intraguild predation: a widespread interaction related to species biology

Intraguild predation (IGP), defined as killing and eating among potential competitors, seems to be a ubiquitous interaction, differing from competition or predation. In the present study we assess the frequency of IGP among 763 potential intraguild prey and 599 potential intraguild predators. Our results indicate that IGP is common in nature, reaching frequencies between 58.4 and 86.7%. A null model suggests that IGP in different groups of predators and prey (i.e. carnivores, omnivores, herbivores, detritivores, or top and intermediate species) have different deviations from a chance expectation, indicating these attributes of species biology as main determinants of IGP persistence. We suggest that IGP satisfies two basic requirements to be considered as important to the trophic structuring of communities. First, its occurrence is not random, rather it is associated with well‐defined attributes of species biology, and secondly, it is a widespread interaction.     

Influence of intraguild predation among generalist insect predators on the suppression of an herbivore population

We evaluated the influence of intraguild predation among generalist insect predators on the suppression of an herbivore, the aphid Aphis gossypii, to test the appropriateness of the simple three trophic level model proposed by Hairston, Smith, and Slobodkin (1960). We manipulated components of the predator community, including three hemipteran predators and larvae of the predatory green lacewing Chrysoperla carnea, in field enclosure/exclosure experiments to address four questions: (1) Do generalist hemipteran predators feed on C. carnea? (2) Does intraguild predation (IGP) represent a substantial source of mortality for C. carnea? (3) Do predator species act in an independent, additive manner, or do significant interactions occur? (4) Can the experimental addition of some predators result in increased densities of aphids through a trophic cascade effect? Direct observations of predation in the field demonstrated that several generalist predators consume C. carnea and other carnivorous arthropods. Severely reduced survivorship of lacewing larvae in the presence of other predators showed that IGP was a major source of mortality. Decreased survival of lacewing larvae was primarily a result of predation rather than competition. IGP created significant interactions between the influences of lacewings and either Zelus renardii or Nabis predators on aphid population suppression. Despite the fact that the trophic web was too complex to delineate distinct trophic levels within the predatory arthropod community, some trophic links were sufficiently strong to produce cascades from higher-order carnivores to the level of herbivore population dynamics: experimental addition of either Z. renardii or Nabis predators generated sufficient lacewing larval mortality in one experiment to release aphid populations from regulation by lacewing predators. We conclude that intraguild predation in this system is wide-spread and has potentially important influences on the population dynamics of a key herbivore.     

Entrapped carrion increases indirect plant resistance and intra‐guild predation on a sticky tarweed

Many plants employ indirect defenses against herbivores; often plants provide a shelter or nutritional resource to predators, increasing predator abundance, and lessening herbivory to the plant. Often, predators on the same plant represent different life stages and different species. In these situations intraguild predation (IGP) may occur and may decrease the efficacy of that defense. Recently, several sticky plants have been found to increase indirect defense by provisioning predatory insects with entrapped insects (hereafter: carrion). We conducted observational studies and feeding trials with herbivores and predators on two sticky, insect‐entrapping asters, Hemizonia congesta and Madia elegans, to construct food webs for these species and determine the prevalence of IGP in these carrion‐provisioning systems. In both systems, intraguild predation was the most common interaction observed. To determine whether IGP was driven by resource abundance, whether it reduced efficacy of this indirect defense and whether stickiness or predator attraction was induced by damage, we performed field manipulations on H. congesta. Carrion supplementation led to an increase in predator abundance and IGP. IGP was asymmetric within the predator guild: assassin bugs and spiders preyed on small stilt bugs but not vice versa. Despite increased IGP, carrion provisions decreased the abundance of the two most common herbivores (a weevil and a mealybug). Overall seed set was driven by plant size, but number of seeds produced per fruit significantly increased with increasing carrion, likely because of the reduction in the density of a seed‐feeding weevil. Observationally and experimentally, we found that carrion‐mediated indirect defense of tarweeds led to much intraguild predation, though predators effectively reduced herbivore abundance despite the increase in IGP.     

Spatial relationships and mechanisms of coexistence between dominant and subordinate top predators

Most forest ecosystems contain a diverse community of top‐level predators. How these predator species interact, and how their interactions influence their spatial distribution is still poorly understood. Here we studied interactions among top predators in a guild of diurnal forest raptors in order to test the hypothesis that predation among competing predators (intraguild predation) significantly affects the spatial distribution of predator species, causing subordinate species to nest farther away from the dominant ones. The study analyzed a guild in southwestern Europe comprising three raptor species. For 8 years we studied the spatial distribution of used nests, breeding phenology, intraguild predation, territory occupancy, and nest‐builder species and subsequent nest‐user species. The subordinate species (sparrowhawk Accipiter nisus) nested farther away from the dominant species (goshawk A. gentilis), which preyed on sparrowhawks but not on buzzards Buteo buteo, and closer to buzzards, with which sparrowhawks do not share many common prey. This presumably reflects an effort to seek protection from goshawks. This potential positive effect of buzzards on sparrowhawks may be reciprocal, because buzzards benefit from old sparrowhawk nests, which buzzards used as a base for their nests, and from used sparrowhawk nests, from which buzzards stole prey. Buzzards occasionally occupied old goshawk nests. These results support our initial hypothesis that interspecific interactions within the raptor guild influence the spatial distribution of predator species in forest ecosystems, with intraguild predation as a key driver. We discuss several mechanisms that may promote the coexistence of subordinate and dominant predators and the spatial assembly of this raptor guild: spatial refuges, different breeding phenology, spatial avoidance, low territory occupancy between neighboring nesting territories, nest concealment and protection, and diet segregation.     

Coexistence of predator and prey in intraguild predation systems with ontogenetic niche shifts

In basic intraguild predation (IGP) systems, predators and prey also compete for a shared resource. Theory predicts that persistence of these systems is possible when intraguild prey is superior in competition and productivity is not too high. IGP often results from ontogenetic niche shifts, in which the diet of intraguild predators changes as a result of growth in body size (life-history omnivory). As a juvenile, a life-history omnivore competes with the species that becomes its prey later in life. Competition can hence limit growth of young predators, while adult predators can suppress consumers and therewith neutralize negative effects of competition. We formulate and analyze a stage-structured model that captures both basic IGP and life-history omnivory. The model predicts increasing coexistence of predators and consumers when resource use of stage-structured predators becomes more stage specific. This coexistence depends on adult predators requiring consumer biomass for reproduction and is less likely when consumers outcompete juvenile predators, in contrast to basic IGP. Therefore, coexistence occurs when predation structures the community and competition is negligible. Consequently, equilibrium patterns over productivity resemble those of three-species food chains. Life-history omnivory thus provides a mechanism that allows intraguild predators and prey to coexist over a wide range of resource productivity.     

The negative effects of pathogen‐infected prey on predators: a meta‐analysis

Intra‐guild predation (IGP) – where a top predator (IG_Pred) consumes both a basal resource and a competitor for that resource (IG_Prey) – has become a fundamental part of understanding species interactions and community dynamics. IGP communities composed of intraguild predators and prey have been well studied; however, we know less about IGP communities composed of predators, pathogens, and resources. Resource quality plays an important role in community dynamics and may influence IGP dynamics as well. We conducted a meta‐analysis on predator–pathogen–resource communities to determine whether resource quality mediated by the pathogen affected predator life‐history traits and if these effects met the theoretical constraints of IGP communities. To do this, we summarized results from studies that investigated the use of predators and pathogens to control insect pests. In these systems, the predators are the IG_Pred and pathogens are the IG_Prey. We found that consumer longevity, fecundity, and survival decreased by 26%, 31% and 13% respectively, when predators consumed pathogen‐infected prey, making the infected prey a low quality resource. Predators also significantly preferred healthy prey over infected prey. When we divided consumers by enemy type, strict predators (e.g. wolf spiders) had no preference while parasitoids preferred healthy prey. Our results suggest that communities containing parasitoids and pathogens may rarely exhibit intraguild predation; whereas, communities composed of strict predators and pathogens are more likely dominated by IGP dynamics. In these latter communities, the consumption of low and high quality resources suggests that IGP communities composed of strict predators, pathogens and prey should naturally persist, supporting IGP theory. Synthesis We investigated how consuming pathogen‐infected prey influence important life‐history parameters of insect predators. Pathogens are used in a variety of biocontrol programs, especially to control crop pests. We found that true predators (i.e. wolf spiders) have no preference for healthy or infected prey and have reduced fecundity, survival and longevity consuming infected prey. However, parasitoids avoided infected prey when possible. In biocontrol programs with multiple control agents, parasitoids and pathogens would do a better job controlling pests as predators would reduce the amount of pathogen available and have reduced fitness from consuming infected prey. However, theory suggests that true predators, prey and pathogens may coexist long term.     

Invasion success in communities with reciprocal intraguild predation depends on the stage structure of the resident population

The probability of individuals being targeted as prey often decreases as they grow in size. Such size‐dependent predation risk is very common in systems with intraguild predation (IGP), i.e. when predatory species interact through predation and competition. Theory on IGP predicts that community composition depends on productivity. When recently testing this prediction using a terrestrial experimental system consisting of two phytoseiid mite species, Iphiseius degenerans as the IG‐predator and Neoseiulus cucumeris as the IG‐prey, and pollen (Typha latifolia) as the shared resource, we could not find the predicted community shift. Instead, we observed that IG‐prey excluded IG‐predators when the initial IG‐prey/IG‐predator ratio was high, whereas the opposite held when the initial ratio was low, which is also not predicted by theory. We therefore hypothesized that the existence of vulnerable and invulnerable stages in the two populations could be an important driver of the community composition. To test this, we first demonstrate that IG‐prey adults indeed attacked IG‐predator juveniles in the presence of the shared resource. Second, we show that the invasion capacity of IG‐predators at high productivity levels indeed depended on the structure of resident IG‐prey populations. Third, we further confirmed our hypothesis by mimicking successive invasion events of IG‐predators into an established population of IG‐prey at high productivity levels, which consistently failed. Our results show that the interplay between stage structure of populations and reciprocal intraguild predation is decisive at determining the species composition of communities with intraguild predation.     

Phenotypic plasticity in anti-intraguild predator strategies: mite larvae adjust their behaviours according to vulnerability and predation risk

Interspecific threat-sensitivity allows prey to maximize the net benefit of antipredator strategies by adjusting the type and intensity of their response to the level of predation risk. This is well documented for classical prey-predator interactions but less so for intraguild predation (IGP). We examined threat-sensitivity in antipredator behaviour of larvae in a predatory mite guild sharing spider mites as prey. The guild consisted of the highly vulnerable intraguild (IG) prey and weak IG predator Phytoseiulus persimilis, the moderately vulnerable IG prey and moderate IG predator Neoseiulus californicus and the little vulnerable IG prey and strong IG predator Amblyseius andersoni. We videotaped the behaviour of the IG prey larvae of the three species in presence of either a low- or a high-risk IG predator female or predator absence and analysed time, distance, path shape and interaction parameters of predators and prey. The least vulnerable IG prey A. andersoni was insensitive to differing IGP risks but the moderately vulnerable IG prey N. californicus and the highly vulnerable IG prey P. persimilis responded in a threat-sensitive manner. Predator presence triggered threat-sensitive behavioural changes in one out of ten measured traits in N. californicus larvae but in four traits in P. persimilis larvae. Low-risk IG predator presence induced a typical escape response in P. persimilis larvae, whereas they reduced their activity in the high-risk IG predator presence. We argue that interspecific threat-sensitivity may promote co-existence of IG predators and IG prey and should be common in predator guilds with long co-evolutionary history.     

Trophic supplements to intraguild predation

Intraguild predation (IGP) is a dominant community module in terrestrial food webs that occurs when multiple consumers feed both on each other and on a shared prey. This specific form of omnivory is common in terrestrial communities and is of particular interest for conservation biology and biological control given its potential to disrupt management of threatened or pest species. Extensive theory exists to describe the dynamics of three-species IGP, but these models have largely overlooked the potential for other, exterior interactions, to alter the dynamics within the IGP module. We investigated how three forms of feeding outside of the IGP module by intraguild predators (i.e. trophic supplementation) affect the dynamics of the predators (both IG predator and IG prey) and their shared resource. Specifically, we examined how the provision of a constant donor-controlled resource, the availability of an alternative prey species, and predator plant-feeding affect the dynamics of IGP models. All three forms of trophic supplements modified the basic expectations of IGP theory in two important ways, and their effects were similar. First, coexistence was possible without the IG prey being a superior competitor for the original shared resource if the IG prey could effectively exploit one of the types of trophic supplements. However, supplements to the IG predator restricted the potential for coexistence. Second, supplements to the IG prey ameliorated the disruptive effects of the IG predator on the suppression of the shared resource, promoting effective control of the resource in the presence of both predators. Consideration of these three forms of trophic supplementation, all well documented in natural communities, adds substantial realism and predictive power to intraguild predation theory.     

Asymmetric larval interactions between introduced and indigenous ladybirds in North America

Understanding the mechanisms that result in the success of introduced species will contribute to predicting future invasions and managing invaded systems. We examined interactions between larvae of two predatory ladybird species recently introduced to North America, Coccinella septempunctata (CS) and Harmonia axyridis (HA), and two indigenous ladybirds, Coccinella transversoguttata (CT) and Hippodamia convergens (HC). By pairing young and old larvae in the laboratory at low and high levels of aphid availability, we assessed the degree of asymmetry in intraguild predation (IGP), the strength of competitive effects on growth and development of larvae escaping predation, and the nature of attack and escape behavior among the species. Interactions were generally asymmetric, with larvae of introduced species acting most frequently as intraguild predators and larvae of indigenous species serving most frequently as intraguild prey (the two Coccinella spp., however, preyed on each other at similar rates). Because they were especially aggressive and because other larvae were least successful in escaping their attacks, larvae of HA had stronger negative effects on larvae of the two indigenous species than did larvae of CS. Such negative effects, expressed most strongly when aphid availability was low, were especially adverse for the smaller of the two indigenous species, HC. In general, older larvae interacted with each other more strongly than young larvae did, and older larvae had especially strong negative effects on young larvae when interactions occurred between age classes. Our results suggest that HA more than CS may represent a threat to indigenous ladybirds as an intraguild predator, and that IGP in turn may play a stronger role for HA than for C. septempunctata in promoting the successful invasion of North America.     

Resource quality,resource availability,and intraguild predation among omnivorous mirids

Intraguild predation (IGP) among predatory species can influence many plant-arthropod associations. However, the relevance of IGP is poorly understood for truly omnivorous species such as those that can complete development on both animal and plant diets. Here we test the hypothesis that IGP among two omnivorous mirids is more common when extraguild food is either absent or not suitable. Laboratory experiments were performed in experimental cages in order to determine the effect of intraguild prey densities and diet availability on direction and intensity of IGP between Dicyphus tamaninii and Macrolophus caliginosus (Heteroptera: Miridae). Intraguild predation was symmetrical between the two mirid species in the absence of alternative food. Increasing densities of intraguild prey enhanced drastically the incidence of IGP. Intraguild predation was reduced when mirids were in the presence of green or red tomato fruits, but the presence of any other extraguild resources had no impact on IGP level. However, when given before the experiments, all resources with the exception of tomato leaves significantly reduced IGP. A second experiment was performed on live plants to compare the results of the previous trials with that obtained in a more natural setting. No IGP was observed when both mirid species were present on a plant. However, development of the intraguild prey (the more vulnerable stage) was hindered by the presence of the intraguild predator. The potential of such results is discussed from community ecology and biological control perspective.     

Role of intraguild predation in aphidophagous guilds

The concept of intraguild predation (IGP) appeared in 1987–1989 to describe trophic interactions within a guild of arthropods inhabiting a sand dune desert: consumers B prey on consumers A and both of them prey on a common resource. Theory predicts that the two types of consumers should only coexist if consumer A is more efficient in the conversion of the common resource than B. As a consequence, this resource is more abundant in the presence than in the absence of intraguild predators. Such a theoretical prediction probably explains the vivid interest shown by ecologists involved in biological control for IGP. It is therefore not surprising that many papers report on IGP among natural enemies of aphids. A close examination of these reported cases indicates that they rarely fulfil the theoretical requirements for IGP. That is, guilds of aphidophagous insects are rarely the theatre of IGP but frequently of interspecific predation. This is confirmed by experimental assessment of the cost of attacking and eating intraguild prey instead of extraguild in ladybird beetles.     

Threat-sensitive anti-intraguild predation behaviour: maternal strategies to reduce offspring predation risk in mites

Predation is a major selective force for the evolution of behavioural characteristics of prey. Predation among consumers competing for food is termed intraguild predation (IGP). From the perspective of individual prey, IGP differs from classical predation in the likelihood of occurrence because IG prey is usually more rarely encountered and less profitable because it is more difficult to handle than classical prey. It is not known whether IGP is a sufficiently strong force to evolve interspecific threat sensitivity in antipredation behaviours, as is known from classical predation, and if so whether such behaviours are innate or learned. We examined interspecific threat sensitivity in antipredation in a guild of predatory mite species differing in adaptation to the shared spider mite prey (i.e. Phytoseiulus persimilis, Neoseiulus californicus and Amblyseius andersoni). We first ranked the players in this guild according to the IGP risk posed to each other: A. andersoni was the strongest IG predator; P. persimilis was the weakest. Then, we assessed the influence of relative IGP risk and experience on maternal strategies to reduce offspring IGP risk: A. andersoni was insensitive to IGP risk. Threat sensitivity in oviposition site selection was induced by experience in P. persimilis but occurred independently of experience in N. californicus. Irrespective of experience, P. persimilis laid fewer eggs in choice situations with the high- rather than low-risk IG predator. Our study suggests that, similar to classical predation, IGP may select for sophisticated innate and learned interspecific threat-sensitive antipredation responses. We argue that such responses may promote the coexistence of IG predators and prey.     

Interactions between invasive and native crustaceans: differential functional responses of intraguild predators towards juvenile hetero-specifics

Intraguild predation (IGP) between invasive and native species can lead to species exclusions or co-existence, dependent on the direction and strength of the interaction. Recently, derivation of ??functional responses?? has been identified as a means of comparing the community impacts of invasive and native species. Here, we employ a novel use of this functional response methodology to evaluate any IGP asymmetries between the invasive Ponto-Caspian amphipod Echinogammarus ischnus and the North American native Gammarus fasciatus. The direction and magnitude of intraguild predation of adult males on hetero-specific adult females has previously been shown to reverse across a water conductivity gradient. This partially explains field patterns, but does not predict the co-existence of the two species observed in many habitats and locations. Here, we compared intraguild predation by both species on each other??s juveniles in high- and low- conductivity water. G. fasciatus has a higher type II functional response towards E. ischnus juveniles compared to the reciprocal interaction. Conductivity did not influence the predation rate on juveniles of either E. ischnus or G. fasciatus. Thus, the male/female IGP advantage to the native G. fasciatus in low conductivity water is compounded by a juvenile IGP asymmetry, which also counteracts the male/female IGP advantage to E. ischnus in high conductivity waters, helping to explain field patterns of exclusion and co-existence. Thus, complex asymmetries in mutual IGP associated with inherent species differences, environmental modulation, and life-history effects can help us understand and predict the population and community level outcomes of species invasions.     

Effects of productivity, disturbance, and ecosystem size on food-chain length: insights from a metacommunity model of intraguild predation

Traditionally, productivity and disturbance have been hypothesized as important determinants of food-chain length. More recently, growing empirical evidence suggests a strong role of ecosystem size. To theoretically explore the effects of basal productivity, disturbance, and ecosystem size on food-chain length, we develop and analyze a metacommunity model of intraguild predation (IGP). The model finds that, when local IGP is weak, increasing basal productivity, weakening disturbance, and increasing ecosystem size will generally increase food-chain length. When local IGP is strong, by contrast, increasing basal productivity or weakening disturbance favors intraguild predators and hinders the coexistence of intraguild predators and intraguild prey, limiting food-chain length. In contrast, increasing ecosystem size can promote coexistence even when local IGP is strong, increasing food-chain length through inserting intraguild prey and changing the degree of omnivory by intraguild predators. Intraguild prey needs to be the superior colonizer to intraguild predators for this to occur. We discuss that these theoretical predictions appear consistent with empirical patterns.     

Effect of size,extraguild prey and habitat complexity on intraguild interactions: a case study with the invasive ladybird <Emphasis Type="Italic">Harmonia axyridis</Emphasis> and the hoverfly <Emphasis Type="Italic">Episyrphus balteatus</Emphasis>

Intraguild predation (IGP) is a widespread interaction between predatory arthropods, and is influenced by several factors. The harlequin ladybird, Harmonia axyridis (Coleoptera: Coccinellidae), has frequently been reported as an intraguild predator of other Coccinellidae, but little is known about its interactions with other aphidophagous predators, including syrphids. This study investigated the incidence of IGP between H. axyridis and Episyrphus balteatus (Diptera: Syrphidae), the most abundant hoverfly species in Europe and a commercially available aphid biocontrol agent. The influence of size, presence of extraguild prey and habitat complexity were investigated through laboratory experiments in Petri dishes and on potted broad bean plants. In both types of arenas, IGP between H. axyridis and E. balteatus was found to be asymmetric, with the coccinellid in the majority of cases being the intraguild predator. There was a significant effect of size on the frequency of IGP. The efficiency of H. axyridis as an intraguild predator increased with the developmental stage. Early instars of E. balteatus were the most vulnerable to IGP. Pupae of either species were not attacked. In the presence of extraguild prey, the frequency of IGP was substantially reduced. However, IGP still occurred, mainly in combinations of older larvae of H. axyridis with first or second instars of E. balteatus. The size of the arena affected the incidence of IGP in combinations with second instars of E. balteatus, but not in combinations with third instars. Field research is needed to elucidate the ecological relevance of IGP among these predators.     

Intraguild predation: The dynamics of complex trophic interactions

There is a long-standing debate in ecology concerning the relative importance of competition and predation in determining community structure. Recently, a novel twist has been added with the growing recognition that potentially competing species are often engaged in predator-prey interactions. This blend of competition and predation is called intraguild predation (IGP). The study of IGP will lead to a reconsideration of many classical topics, such as niche shifts, species exclusion and cascading interactions in food webs. Theoretical models suggest that a variety of alternative stable states are likely in IGP systems, and that intermediate predators should tend to be superior in exploitative competition. Many field studies support these expectations. IGP is also important in applied ecological problems, such as the conservation of endangered species and fisheries management.     

Intraguild predation with spatially structured interactions

Consumer–resource interactions with intraguild predation (IGP) were studied in a spatial setting (i.e., predators catch prey and individuals reproduce within local neighborhoods only). Pair approximation (a method for deriving ordinary differential equations that approximate the dynamics of a community that interacts in a lattice environment) was used to study the effect of spatially structured species interactions. An individual-based computer simulation was used to extend the study to a case with spatially variable resource densities. The qualitative results of the pair approximation model were similar to those of the corresponding non-spatial model. However, the spatial model predicted coex((istence over a wider range of parameters than the non-spatial model when intraguild prey are nutritionally valuable to intraguild predators. Spatially heterogeneous resource distributions and spatially structured interaction could overturn the qualitative predictions of non-spatial models.     

Tiger and leopard co-occurrence: intraguild interactions in response to human and livestock disturbance

Intraguild interactions have important implications for carnivore demography and conservation. Differences in how predators respond to different forms of disturbance might alter their interaction patterns. We sought to understand how human and livestock disturbance impact co-occurrence of sympatric large carnivores such as tiger (Panthera tigris) and leopard (P. pardus) and thereby mediate the intraguild interaction pattern to enable coexistence of the species in a human-dominated landscape. We surveyed 361 locations in Chitwan National Park, Nepal, to examine how prey abundance and disturbance factors such as human and livestock presence might influence habitat use by tigers and leopards independently and when co-occurring. Single-species single-season models and two-species single-season models were developed to examine hypotheses on unconditional detection and occupancy and species interaction respectively. Pervasive human use of the park had negative impacts on tiger occupancy while the abundance of prey had a positive influence. Despite significant prey overlap between tigers and leopards, none of the native prey species predicted leopard habitat occupancy. However, habitats used extensively by livestock were also used by leopards. Further, we found strong evidence of intraguild competition. For instance tiger occupancy was higher in prey-rich areas and leopard occupancy was low in the sites where tigers were present. These findings, and a species interaction factor of < 1 clearly indicate that leopards avoid tigers, but their use of areas of disturbance enables them to persist in fringe habitats. We provide empirical evidence of how intraguild interaction may result in habitat segregation between competing carnivores, while also showing that human and livestock use of the landscape create disturbance patterns that facilitate co-occurrence of the predators. Thus, because large carnivores compete, some disturbance may mediate coexistence in small protected areas. Understanding such interactions can help address important conservation challenges associated with maintaining diverse carnivore communities in small or disturbed landscapes.     

Using mean first passage times to quantify equilibrium resilience in perturbed intraguild predation systems

Regime shift inducibility depends on equilibrium resilience, which depends on species interactions. When species interactions include intraguild predation (IGP), integrated pest management may induce regime shifts because enhancing the abundance of intraguild predators simultaneously increases competition with, and predation on, invasive prey. To explore the dynamical consequences of such manipulations, we use a bistable, deterministic IGP model with stochastic removals that perturb invader density from the high-density equilibrium. We quantify the combined effects of IGP and such perturbations in terms of mean first passage times (MFPTs) to target invader densities such as thresholds between regimes. Analytical MFPTs compare favorably with those generated by Monte Carlo numerical solutions of the stochastically perturbed IGP model. MFPTs can therefore usefully quantify equilibrium resilience in terms of perturbation schedules. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.