Predator Interference Research Articles

A mechanistic model for interference and Allee effect in the predator population

We present the results of simulations in an individual-based model describing spatial movement and predator-prey interaction within a closed rectangular habitat. Movement of each individual animal is determined by local conditions only, so any collective behavior emerges owing to self-organization. It is shown that the pursuit of prey by predators entails predator interference, manifesting itself at the population level as the dependency of the trophic function (individual ration) on predator abundance. The stabilizing effect of predator interference on the dynamics of a predator-prey system is discussed. Inclusion of prey evasion induces apparent cooperation of predators and further alters the functional response, giving rise to a strong Allee effect, with extinction of the predator population upon dropping below critical numbers. Thus, we propose a simple mechanistic interpretation of important but still poorly understood behavioral phenomena that underlie the functioning of natural trophic systems.

The asymptotic behavior of a Chemostat model with Crowley–Martin type functional response and time delays

In this paper, we introduce an improved Chemostat model with Crowley–Martin type functional response and time delays. By constructing Lyapunov functionals, the global asymptotic stability of the equilibria is shown in the case of a single species. The conditions for the global asymptotical stability of the model with time delays are obtained via monotone dynamical systems in the case of two species. Our results demonstrate that the effects of predator interference may result in coexistence of two species.

The role of top predator interference on the dynamics of a food chain model

In this paper, the effects of top predator interference on the dynamics of a food chain model involving an intermediate and a top predator are considered. It is assumed that the interaction between the prey and intermediate predator follows the Volterra scheme, while that between the top predator and its favorite food depends on Beddington–DeAngelis type of functional response. The boundedness of the system, existence of an attracting set, local and global stability of non-negative equilibrium points are established. Number of the bifurcation and Lyapunov exponent bifurcation diagrams is established. It is observed that, the model has different types of attracting sets including chaos. Moreover, increasing the top predator interference stabilizes the system, while increasing the normalization of the residual reduction in the top predator population destabilizes the system.

Modeling multiple nonconsumptive effects in simple food webs: a modified Lotka-Volterra approach

Nonconsumptive effects are an important component of many ecological systems. Yet, modeling these interactions has proven challenging, with the few current models being either overly simplified or very complex. Here I build on the idea of predator interference to derive a model that is both flexible and intuitive. The model is derived using a 4-species food web that includes multiple nonconsumptive effects (NCEs) and interactions among them, though this approach may be adaptable to larger ecological communities. I apply this model to 2 example systems—a stream community and a coffee insect community—and discuss how the incorporation of NCEs changes the dynamics of each system. In the Appendix, I discuss the empirical data and statistics necessary to parameterize the model in hopes that future empirical studies will include additional experiments that can inform modeling frameworks such as the one proposed here. Empirically informed theoretical studies will help evaluate the importance of NCEs on the long-term dynamics of simple communities. Key words: coexistence, Crowley–Martin model, food web modules, functional response, nonconsumptive effects, predator interference. [Behav Ecol]

Predator density and competition modify the benefits of group formation in a shoaling reef fish

Synthesis Predation risk experienced by individuals living in groups depends on the balance between predator dilution, competition for refuges, and predator interference or synergy. These interactions operate between prey species as well: the benefits of group living decline in the presence of an alternative prey species. We apply a novel model-fitting approach to data from field experiments to distinguish among competing hypotheses about shifts in predator foraging behavior across a range of predator and prey densities. Our study provides novel analytical tools for analyzing predator foraging behavior and offers insight into the processes driving the dynamics of coral reef fish. Studies of predator foraging behavior typically focus on single prey species and fixed predator densities, ignoring the potential importance of complexities such as predator dilution; predator-mediated effects of alternative prey; heterospecific competition; or predator–predator interactions. Neglecting the effects of prey density is particularly problematic for prey species that live in mixed species groups, where the beneficial effects of predator dilution may swamp the negative effects of heterospecific competition. Here we use field experiments to investigate how the mortality rates of a shoaling coral reef fish (a wrasse: Thalassoma amblycephalum), change as a result of variation in: 1) conspecific density, 2) density of a predator (a hawkfish: Paracirrhites arcatus), and 3) presence of an alternative prey species that competes for space (a damselfish: Pomacentrus pavo). We quantify changes in prey mortality rates from the predator's perspective, examining the effects of added predators or a second prey species on the predator's functional response. Our analysis highlights a model-fitting approach that discriminates amongst multiple hypotheses about predator foraging in a community context. Wrasse mortality decreased with increasing conspecific density (i.e. mortality was inversely density-dependent). The addition of a second predator doubled prey mortality rates, without significantly changing attack rate or handling time – i.e. there was no evidence for predator interference. The presence of a second prey species increased wrasse mortality by 95%; we attribute this increase either to short-term apparent competition (predator aggregation) or to a decrease in handling time of the predator (e.g. through decreased wrasse vigilance). In this system, 1) prey benefit from intraspecific group living though a reduced predation risk, and 2) the benefit of group living is reduced in the presence of an alternative prey species.

Does predator interference cause alternative stable states in multispecies communities?

Whereas it is well known that simple ecological mechanisms may promote stability in simple species models, their consequences for stability and resilience in multispecies communities are largely unexplored. Here, we studied the effect of predator interference on the occurrence of alternative attractors and complex dynamics in randomly constructed multispecies predator–prey communities. We studied three types of interference: random interference (“asymmetric”), random interference but symmetrical between pairs of predators (“symmetric”), and interference among only the same species (“conspecific”). In all cases predator interference increased the average number of alternative attractors, whereas at the same time it reduced the emergence of oscillatory or chaotic dynamics. Our findings demonstrate a contrasting effect of predator interference on the stability of a community: on the one hand it reduces cycles and chaos in the dynamics, on the other hand predator interference increases the likelihood that communities may undergo critical transitions between multiple stable states.

Cannibalism in red king crab, Paralithodes camtschaticus (Tilesius, 1815): Effects of habitat type and predator density on predator functional response

Red king crab, Paralithodes camtschaticus, an important fishery species in Alaska, exhibits cannibalism both within and among age classes. Cannibalism in crab species can be an important determinant of recruitment success, and this might be especially important in king crab because year-0 and year-1 crab occupy the same habitat types in the wild. In this study we used laboratory experiments to determine the predator functional response, or the effect of prey density on predation rates of year-1 crab preying on year-0 crab in three different habitat types: Sand, which was unstructured soft sediment, Whole Shell, which was whole clam valves, and Shell Hash, which was smaller pieces of crushed shell. We also examined how predator density (one or two predators) affects the functional response. The data was fit to Type I, or density independent, Type II, or inversely density dependent, and Type III, or density dependent, functional response models and the best fit model was chosen using Akaike's information criterion. The functional response was a Type II in all habitat types; however, the predation rate was lower at all prey densities in the Whole Shell habitat than in Shell Hash and Sand. The functional response was a Type II at both predator densities as well. The presence of a second predator decreased both the attack rate and the handling time, resulting in slightly lower predation rates at low prey densities, and slightly higher predation rates at high prey densities when compared to the single predator treatment. This indicates a low level of predator interference. This work has implications for potential stock enhancement activities, as year-1 crab could inhibit enhancement success though cannibalism of introduced year-0 crab, especially given the destabilizing nature of the Type II functional response. A potential solution would be to enhance a given area only every other year to give previous cohorts a chance to start podding in less complex habitats. Future work should examine whether the presence of alternative prey changes the functional response to a Type III, as this would give year-0 crabs a low‐density refuge from predation.

More than a meal… integrating non‐feeding interactions into food webs

Organisms eating each other are only one of many types of well documented and important interactions among species. Other such types include habitat modification, predator interference and facilitation. However, ecological network research has been typically limited to either pure food webs or to networks of only a few (<3) interaction types. The great diversity of non-trophic interactions observed in nature has been poorly addressed by ecologists and largely excluded from network theory. Herein, we propose a conceptual framework that organises this diversity into three main functional classes defined by how they modify specific parameters in a dynamic food web model. This approach provides a path forward for incorporating non-trophic interactions in traditional food web models and offers a new perspective on tackling ecological complexity that should stimulate both theoretical and empirical approaches to understanding the patterns and dynamics of diverse species interactions in nature.

Rabbits protecting birds: Hypopredation and limitations of hyperpredation

Biological invasions often damage island ecosystems. One such damaging consequence of biological invasions is hyperpredation. Hyperpredation is the increase in predation pressure from a generalist predator following the introduction of an alternative prey, typically a consequence of apparent competition between the two prey. Models for this have been devised that demonstrate this effect. However, hyperpredation may not always occur or may not always occur at the same strength. Here, we investigate how different mechanisms affect the magnitude of hyperpredation: (i) saturation of the predator's functional response, (ii) predator interference and (iii) non-predatory competition among predators. We find that all three mechanisms generally reduce hyperpredation. Predator saturation can actually overturn hyperpredation into hypopredation, an increase in native prey, as a result of apparent predation between the two prey. This occurs when the alternative prey is ‘poisoned prey’, i.e. prey that have a handling time cost greater than the nutritional benefit for the predator. Consuming ‘poisoned prey’ can result in an increase or decrease in predator density. Conversely, we also identify scenarios in which interference and competition may increase hyperpredation. Based on these insights, we conclude that the invasion of established ecosystems by non-native prey can lead to more diverse consequences than previously thought. Potential control measures should take these effects into account.

A Predator–Prey Model with a Holling Type I Functional Response Including a Predator Mutual Interference

The most widely used functional response in describing predator–prey relationships is the Holling type II functional response, where per capita predation is a smooth, increasing, and saturating function of prey density. Beddington and DeAngelis modified the Holling type II response to include interference of predators that increases with predator density. Here we introduce a predator-interference term into a Holling type I functional response. We explain the ecological rationale for the response and note that the phase plane configuration of the predator and prey isoclines differs greatly from that of the Beddington–DeAngelis response; for example, in having three possible interior equilibria rather than one. In fact, this new functional response seems to be quite unique. We used analytical and numerical methods to show that the resulting system shows a much richer dynamical behavior than the Beddington–DeAngelis response, or other typically used functional responses. For example, cyclic-fold, saddle-fold, homoclinic saddle connection, and multiple crossing bifurcations can all occur. We then use a smooth approximation to the Holling type I functional response with predator mutual interference to show that these dynamical properties do not result from the lack of smoothness, but rather from subtle differences in the functional responses.

Interference competition and group size effect in sika deer (Cervus nippon) at salt licks

Competition has long been considered as a confounding factor of group size effect but the understanding of interference competition is rudimentary for the difficulty in disentangling interference competition from scramble competition adequately. Here, we analysed remote-camera video records of wild sika deer (Cervus nippon) at salt licks in southern China from March 1, 2006 to November 30, 2008 to investigate how interference competition and predation risk interacted on vigilance behaviour. Scramble competition is negligible at salt licks; therefore, we could focus our interest in interference competition. We used linear mixed model to compare vigilance, licking and aggression behaviours among females with and without fawn as well as males with different group sizes to identify the primary role of vigilance behaviour in sika deer. In total, 168 individuals were recorded and observation time was 2,733.04 min. We found that deer spent much time on vigilance and scanned frequently in spring and winter, and females with fawn spent more time on vigilance than females without fawn, suggesting vigilance for predation risk. Aggression ratio increased first and then decreased, while scan frequency continued to decline and then slightly increased when group size increased from two to seven, implying vigilance for interference competition. Our results suggested vigilance in sika deer was influenced by both predation risk and interference competition, but was mainly driven by predation risk even at sites with intense interference competition. Our results of interference competition shed some light on finding the underlying mechanism of group size effect in wild populations.

Diversity and invasion within a predator community: impacts on herbivore suppression

Summary 1. Management strategies to enhance ecosystem services in agroecosystems often seek to increase predator biodiversity. Invaders commonly dominate predator communities in agricultural landscapes, however, and the impacts of exotic predators on native predators and ecosystem services are largely unknown. Exotic predators may complement native predator diversity and enhance herbivore suppression, or they may disrupt herbivore suppression through predator interference. 2. We examined the impacts of a dominant exotic predator within the diverse predator community of a California vineyard. Interactions between the exotic wandering spider Cheiracanthium mildei, its closest native ecological homologue (the wandering spider Anyphaena pacifica) and a native spider displaying a different hunting mode (the cobweb‐weaving spider Theridion melanurum) were tested in a manipulative field experiment, with the grape leafhopper Erythroneura elegantula acting as a shared herbivore prey source. 3. We found that the exotic wandering spider suppressed both grape leafhoppers and other unmanipulated leafhopper species that were present in cages. Native spiders had little or no impacts on leafhopper suppression. Thus, C. mildei appears to drive predatory impacts in this system, although evidence also indicated that it is limited by intraspecific interactions. The superior predatory ability displayed by this spider may be shared by other invasive predators that dominate agroecosystems. 4. Despite its effects on leafhoppers, C. mildei negatively impacted a range of spider species, including A. pacifica, T. melanurum, and other unmanipulated native spiders. These impacts are likely to have been mediated through intraguild predation. The wandering hunting mode of C. mildei may have facilitated its role as an intraguild predator. 5. Synthesis and applications. Our results highlight the sometimes conflicting aims of biological control and conservation. Here, a dominant invasive predator increased ecosystem services but also caused declines in numbers of native predators. As disturbed conditions in agroecosystems are likely to put invasive predators at an adaptive advantage, efforts to conserve biodiversity in agricultural landscapes should focus on shifting the outcomes of species interactions to favour native species.

Global dynamics of a predator–prey model

This paper deals with the dynamics of a predator–prey model with Hassell–Varley–Holling functional response. First, we show that the predator coexists with prey if and only if predator's growth ability is greater than its death rate. Second, using a blow-up technique, we prove that the origin equilibrium point is repelling and extinction of both predator and prey populations is impossible. Third, the local and global stability of the positive steady state coincide when the predator interference is large. Finally, for a typical biological case, we show instability of the positive equilibrium implies global stability of the limit cycle. Numerical simulations are carried out for a hypothetical set of parameter values to substantiate our analytical findings.

Predator–prey model of Beddington–DeAngelis type with maturation and gestation delays

A predator–prey model of Beddington–DeAngelis type with maturation and gestation delays is formulated and analyzed. This two-delay model is similar to the stage-structured model by Liu and Beretta [S. Liu, E. Beretta, Stage-structured predator–prey Model with the Beddington–DeAngelis functional response, SIAM J. Appl. Math. 66 (2006) 1101–1129] but contains an extra gestation delay term. Criteria for permanence and for predator extinction as well as the global attractiveness of the interior equilibrium are derived. The combined effects of the two delays and the degree of predator interference on the dynamical behaviors of the coexistence equilibrium are also studied both analytically and numerically. It is shown that complicated behaviors including chaotic and multi-periodic solutions may occur with the introduction of gestation delay, and that the predator interference can stabilize the system by simplifying the dynamical behaviors and enlarging the stability parameter fields.

Spatial heterogeneity and functional response: an experiment in microcosms with varying obstacle densities

Spatial heterogeneity of the environment has long been recognized as a major factor in ecological dynamics. Its role in predator-prey systems has been of particular interest, where it can affect interactions in two qualitatively different ways: by providing (1) refuges for the prey or (2) obstacles that interfere with the movements of both prey and predators. There have been relatively fewer studies of obstacles than refuges, especially studies on their effect on functional responses. By analogy with reaction-diffusion models for chemical systems in heterogeneous environments, we predict that obstacles are likely to reduce the encounter rate between individuals, leading to a lower attack rate (predator-prey encounters) and a lower interference rate (predator-predator encounters). Here, we test these predictions under controlled conditions using collembolans (springtails) as prey and mites as predators in microcosms. The effect of obstacle density on the functional response was investigated at the scales of individual behavior and of the population. As expected, we found that increasing obstacle density reduces the attack rate and predator interference. Our results show that obstacles, like refuges, can reduce the predation rate because obstacles decrease the attack rate. However, while refuges can increase predator dependence, we suggest that obstacles can decrease it by reducing the rate of encounters between predators. Because of their opposite effect on predator dependence, obstacles and refuges could modify in different ways the stability of predator-prey communities.

Ratio‐ and Predator‐Dependent Functional Forms for Predators Optimally Foraging in Patches

Functional forms of predator-prey interactions are developed for predators optimally foraging on prey distributed in patches. The model uses mean free-path-length theory to develop functional forms for two idealized behaviors of prey in patches. For congregating prey that maintain a fixed density, for example, fish schools, the predation rate has a ratio-dependent form, and predator interference depends only on predator density. For sessile prey, which maintain a fixed patch size, a new predator-dependent form emerges in which predator interference depends on both prey and predator densities. The Beddington-DeAngelis equation is a special case of the sessile form. The model provides behavioral and biological criteria with which to select the functional form and ranges of coefficients appropriate for a particular food web. Finally, the model illustrates that behavior is an essential factor in predator-prey dynamics.

Body‐mass constraints on foraging behaviour determine population and food‐web dynamics

Abstract 1. In community and population ecology, there is a chronic gap between the classic Eltonian ecology describing patterns in abundance and body mass across species and ecosystems and the more process oriented foraging ecology addressing interactions and quantitative population dynamics. However, this dichotomy is arbitrary, because body mass also determines most species traits affecting foraging interactions and population dynamics. 2. In this review, allometric (body‐mass dependent) scaling of handling times and attack rates are documented, whereas body‐mass effects on Hill exponents (varying between hyperbolic type II and sigmoid type III functional responses) and predator interference coefficients are lacking. This review describes how these allometric relationships define a biological plausible parameter space for population dynamic models. 3. Consistent with the classic Eltonian description, species co‐existence in consumer‐resource models and tri‐trophic food chains is restricted to intermediate consumer‐resource body‐mass ratios. Allometric population dynamic models allow understanding the processes of energy limitation and unstable dynamics leading to this restriction. Complex food webs are stabilized by high predator‐prey body‐mass ratios, which are consistent with those found in natural ecosystems. These high body‐mass ratios yield positive diversity‐stability and complexity‐stability relationships thus supporting the classic picture of ecosystem stability. 4. Allometric‐trophic network models, based on body mass and trophic information from ecosystems, bridge the gap between Eltonian community patterns and process‐oriented foraging ecology and provide a new means to describe the dynamics and functioning of natural ecosystems.

Impacts of Foraging Facilitation Among Predators on Predator-prey Dynamics

Whereas impacts of predator interference on predator-prey dynamics have received considerable attention, the "inverse" process-foraging facilitation among predators-have not been explored yet. Here we show, via mathematical models, that impacts of foraging facilitation on predator-prey dynamics depend on the way this process is modeled. In particular, foraging facilitation destabilizes predator-prey dynamics when it affects the encounter rate between predators and prey. By contrast, it might have a stabilizing effect if the predator handling time of prey is affected. Foraging facilitation is an Allee effect mechanism among predators and we show that for many parameters, it gives rise to a demographic Allee effect or a critical predator density in need to be crossed for predators to persist. We explore also the effects of predator interference, to make the picture "symmetric" and complete. Predator interference is shown to stabilize predator-prey dynamics once its strength is not too high, and thus corroborates results of others. On the other hand, there is a wide range of model parameters for which predator interference gives rise to three co-occurring co-existence equilibria. Such a multi-equilibrial regime is rather robust as we observe it for all the functional response types we explore. This is a previously unreported phenomenon which we show cannot occur for the Beddington-DeAngelis functional response. An interesting topic for future research thus might be to seek for general conditions on predator functional responses that would produce multiple co-existence equilibria in a predator-prey model.

Dynamical consequences of predator interference in a tri-trophic model food chain

A model food chain involving a specialist and a generalist predator is proposed and studied. One of the salient features of this model food chain is that it combines both the schemes (Volterra and Leslie) of modeling predator–prey interaction in one system in such a way that the demerits of these individual formulations are suppressed and the resulting model system represents a common unit of real world food webs. The stability analysis of the proposed model is carried out. The Hopf bifurcation conditions of the positive equilibrium point are established. Our numerical computations show that chaotic dynamics is sensitive to changes in values of parameters measuring attributes of either interacting populations or their environments. Two dimensional parameter scans suggest that the model food chain displays short-term recurrent chaos. This can be regarded as a plausible explanation for why it has been so difficult to detect deterministic chaos in natural populations.

Habitat complexity alters lethal and non-lethal olfactory interactions between predators and prey

Habitat complexity often modifies rates of prey capture by visual predators, but little is known about how structural features affect non-visual olfactory consumers. Laboratory studies indi- cate that turbulent water flow over complex bedforms mixes chemical information in ways that con- fuse some olfactory foragers but improve the odor-tracking abilities of burrowing gastropods (whelks Busycon spp.). We augmented bottom roughness in a soft-sediment estuary to test the hypothesis that turbulent mixing of chemical attractants in the field increases whelk predation on hard clams Merce- naria mercenaria. Thin flat layers of shell fragments around the perimeter of experimental clam plots increased turbulent mixing of prey odors relative to those emanating from control plots. Assessment of prey mortality after 4 wk of exposure revealed that whelk predation on clams surrounded by shells was significantly higher than on clams surrounded by natural sediment. A second set of experiments showed that open prey plots containing a centrally caged (non-lethal) whelk experienced lower mor- tality due to avoidance responses of prey, but surrounding those plots with shells counteracted the non-lethal predator effect and led to significantly greater consumption by naturally foraging whelks. Shell treatments did not increase prey feeding or reduce predator interference. Results suggest that whelks hunt more successfully when bottom roughness increases turbulent mixing of prey chemicals or disrupts prey abilities to detect and respond to predator odors. When integrated over time, habitat- related differences in chemical transfer and olfactory behavior could have important implications for populations of both predators and prey.