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Understanding Batesian mimicry is a classic problem in evolutionary biology. In Batesian mimicry, a defended species (the model) is mimicked by an undefended species (the mimic). Prior theories have emphasized the role of predator behavior and learning as well as evolution in model-mimic complexes but have not examined the role of population dynamics in potentially governing the relative abundances and even persistence of model-mimic systems. Here, we examined the effect of the population dynamics of predators and alternative prey on the prevalence of warning-signaling prey composed of models and mimics. Using optimal foraging theory and signal detection theory, we found that the inclusion of predator and alternative prey population dynamics could reverse traditional theoretical predictions: as alternative prey increase in numbers, mimics suffer because larger populations of predators are maintained, resulting in apparent competition. Under some circumstances, apparent competition affects model populations as well, although not as severely as it affects mimics. Our results bear on the intriguing puzzle that in nature warning signals are relatively scarce, yet experiments suggest that such signals can be highly advantageous. The availability of alternative prey and numerical responses by predators can overwhelm advantages observed in experiments to keep warning signals in model-mimic systems relatively scarce. [ABSTRACT FROM AUTHOR]

Warning signals are a striking example of natural selection present in almost every ecological community – from Nordic meadows to tropical rainforests, defended prey species and their mimics ward off potential predators before they attack. Yet despite the wide distribution of warning signals, they are relatively scarce as a proportion of the total prey available, and more so in some biomes than others. Classically, warning signals are thought to be governed by positive density‐dependent selection, i.e. they succeed better when they are more common. Therefore, after surmounting this initial barrier to their evolution, it is puzzling that they remain uncommon on the scale of the community. Here, we explore factors likely to determine the prevalence of warning signals in prey assemblages. These factors include the nature of prey defences and any constraints upon them, the behavioural interactions of predators with different prey defences, the numerical responses of predators governed by movement and reproduction, the diversity and abundance of undefended alternative prey and Batesian mimics in the community, and variability in other ecological circumstances. We also discuss the macroevolution of warning signals. Our review finds that we have a basic understanding of how many species in some taxonomic groups have warning signals, but very little information on the interrelationships among population abundances across prey communities, the diversity of signal phenotypes, and prey defences. We also have detailed knowledge of how a few generalist predator species forage in artificial laboratory environments, but we know much less about how predators forage in complex natural communities with variable prey defences. We describe how empirical work to address each of these knowledge gaps can test specific hypotheses for why warning signals exhibit their particular patterns of distribution. This will help us to understand how behavioural interactions shape ecological communities. [ABSTRACT FROM AUTHOR]

COMMENTARY Towardecoevolutionarydynamics Karl Sigmund a,1 and Robert D. Holt b  AsbiologistAndrewHendryrecentlywrote,"research initiatives in ecology and evolution have periodically dated but never married" (1). Maynard Smith was the first to apply this insight to the frequency-dependent selection of phenotypic traits, using game theory (5). Ecoevolution The relation of evolution with ecology seems more promising (1, 9).Thesuccessofagiventraitoftendependsonthefrequencyof some trait in another population, as well as on population densities. Evolutionary Game Theory Often, the success of a trait depends on the trait values of other members of its population, and on their abundance. [Extracted from the article]

Ilkka Hanski is most widely known for his seminal contributions to metapopulation ecology, both theoretical and empirical. But he also made many important and wide-ranging contributions to other arenas of ecological inquiry, including in particular predator-prey, host-parasitoid, and host-pathogen interactions. This paper provides an overview of his work in trophic ecology, ranging from individual behavior of foraging predators and fleeing prey, up to effects of spatial patchiness on the persistence of specialist natural enemies, and even the determinants of food chain length. In recent years, his work on food web interactions took on an increasingly genetic and evolutionary slant. In this paper, I also return to two theoretical models that I discussed over the years with Ilkka, where we contemplated carrying out collaborative work, but never managed to do so. The first of these models involves how habitat patchiness might moderate apparent competition between prey species. The second of these has to do with splicing evolutionary dynamics into metapopulation models, so as to craft hypotheses about how food chain length might be influenced by the coevolutionary struggle between predators and their prey. I developed simple models of the sort we should have explored together, in the style we would have used at the time of our conversations on these themes, in homage to my memory of our interactions. [ABSTRACT FROM AUTHOR]

Many ecological systems are characterized by brief periods of increased resource availability called resource pulses. Empirical studies suggest that some populations of primary consumers grow rapidly in response to resource pulses, but others instead remain at low abundance despite increases in resource availability. Previous theory suggests that the lack of increase in primary consumers might be due to predators, which can respond to increased prey density both numerically, by increasing their own population, and functionally, by killing prey at a faster rate. The complexity of potential population responses to resource pulses can be assessed with simulations, but analytical conditions determining when one observes qualitatively distinct dynamics have yet to be identified. Here we use a graphical method based on a bifurcation diagram to derive the conditions leading to qualitatively distinct steady state and transient prey population dynamics as levels of predation (abundance and diversity) vary. When predation thresholds are crossed, consumer populations respond numerically to increases in their resources and provide a secondary resource pulse to their predators and parasites. These community dynamics have broad implications for the impact of changing predator communities on insect and rodent population outbreaks, which are economically and epidemiologically important. [ABSTRACT FROM AUTHOR]

Abstract: Predator–prey interactions play out in a physical matrix defined at least to some extent by the quantity and architecture of plants. Ambush predators for instance might more effectively encounter and capture prey in thick vegetation than in thin, open vegetation with good visibility. Yet these vegetation attributes are themselves potentially influenced by the intensity of herbivory, which in turn reflects the magnitude of predation. This intertwining of trophic interactions and basal biomass leads to a largely unexplored feedback in food chain dynamics. In this paper, we examine a number of extensions of standard predator–prey and food chain models that incorporate this kind of “bottom–up” influence on trophic interactions. Even simple models reveal a range of interesting behaviors. For instance, vegetation-dependent attack rates can generate alternative stable states, in one of which the predator effectively limits herbivores to low numbers, freeing plants of substantial regulation by herbivory, and in the other of which the predator is either absent, or present as an ineffective top trophic level. This can occur both in models in which the top predator is a specialist, completely dependent upon the herbivore, and in models in which the top predator is a generalist, inflicting mortality upon the focal prey species, but itself sustained in numbers by alternative prey. Another possibility is that the feedback between basal biomass and attack rates destabilizes the trophic interactions, leading to sustained oscillations in food chains. Comparable effects can arise if handling times depend upon vegetation biomass. These models illustrate the rich complexity of effects that can arise even in relatively simple community models, once one takes into account the range of potential feedback effects that are potentially present. [Copyright &y& Elsevier]

Consumer fronts occur when grazers or predators aggregate in bands along the edges of a resource. Our review reveals that consumer fronts are a common phenomenon in nature, occur in many different ecosystems, and are triggered by universal mechanisms: External forces locally increase top-down control beyond prey carrying and/or renewal capacity, and resource-dependent movement leads to consumer aggregation along the edge of the remaining prey population. Once formed, consumer fronts move through systems as spatially propagating waves, self-reinforced via intense overexploitation and amplified by density-dependent feedbacks. When consumer fronts are spatially restricted, they generate patchiness. In contrast, when consumer fronts are expansive, they can lead to runaway responses that cause large-scale ecosystem degradation and regime shifts. We conceptualize a synergistic stress hypothesis and model that highlight how coupled intensification of physical stress and enhanced consumer pressure can trigger increased occurrence of consumer fronts and decreased system stability and resilience. With escalating climate change and food-web modification, the physical and biological conditions favoring consumer-front formation will likely become a common feature of many ecosystems. [ABSTRACT FROM AUTHOR]

Saturating functional responses are a unifying principle in ecology, influencing processes at organizational levels from dietary specialization in individuals, to population instability, to community-level indirect interactions among alternative prey. These effects are interrelated. We explore a predator–prey model and demonstrate that unstable dynamics promote coexistence of specialist and generalist predators, when the specialist attacks only high-quality prey, and the generalist attacks high- and low-quality prey (that alone cannot maintain the predator). Coexisting specialist and generalist predators are vulnerable to invasion and replacement by predators with fixed partial preferences. The evolutionarily stable partial preference increases with increasing dynamic instability, but typically declines with increasing abundance of the low-quality prey. Coexisting specialist and generalist consumers, or partial preferences, typically reduce the potential for poor-quality prey to indirectly benefit high-quality prey. We suggest that dynamic instability may also contribute to the evolutionary maintenance of seemingly maladaptive oviposition choices by insect parasitoids. [ABSTRACT FROM PUBLISHER]

Background: Community interactions can produce complex dynamics with counterintuitive responses. Synanthropic community members are of increasing practical interest for their effects on biodiversity and public health. Most studies incorporating introduced species have been performed on islands where they may pose a risk to the native fauna. Few have examined their interactions in urban environments where they represent the majority of species. We characterized house cat (Felis catus) predation on wild Norway rats (Rattus norvegicus), and its population effects in an urban area as a model system. Three aspects of predation likely to influence population dynamics were examined; the stratum of the prey population killed by predators, the intensity of the predation, and the size of the predator population. Methodology/Principal Findings: Predation pressure was estimated from the sizes of the rat and cat populations, and the characteristics of rats killed in 20 alleys. Short and long term responses of rat population to perturbations were examined by removal trapping. Perturbations removed an average of 56% of the rats/alley but had no negative long-term impact on the size of the rat population (49.6±12.5 rats/alley and 123.8±42.2 rats/alley over two years). The sizes of the cat population during two years (3.5 animals/alley and 2.7 animals/alley) also were unaffected by rat population perturbations. Predation by cats occurred in 9/20 alleys. Predated rats were predominantly juveniles and significantly smaller (144.6 g±17.8 g) than the trapped rats (385.0 g±135.6 g). Cats rarely preyed on the larger, older portion of the rat population. Conclusions/Significance: The rat population appears resilient to perturbation from even substantial population reduction using targeted removal. In this area there is a relatively low population density of cats and they only occasionally prey on the rat population. This occasional predation primarily removes the juvenile proportion of the rat population. The top predator in this urban ecosystem appears to have little impact on the size of the prey population, and similarly, reduction in rat populations doesn't impact the size of the cat population. However, the selected targeting of small rats may locally influence the size structure of the population which may have consequences for patterns of pathogen transmission. [ABSTRACT FROM AUTHOR]

The author talks about the uses and abuses of comparative demography. The author argues about the context of how spatial variation in predation pressure maps onto spatial variation in realized mortality rates. The author suggests that whether or not the expected relationship between predation pressure and mortality rate holds will depend on the nature of density dependence in the prey population. The author states that examining temporal trends in demography is a valuable and essential tool when monitoring populations trending towards extinction.

A rich body of theoretical literature now exists focused on the three-species module of intraguild predation (IGP), in which a top predator both attacks and competes with an intermediate predator. Simple models of intraguild predation are often unstable, either because one consumer is excluded, or because sustained oscillations emerge from long feedback loops. Yet, many natural IGP systems robustly persist. Standard models of intraguild predation simplify natural systems in crucial ways that could influence persistence; in particular, many empirical IGP systems are embedded in communities with alternative prey species. We briefly review the key conclusions of standard three-species IGP theory, and then present results of theoretical explorations of how alternative prey can influence the persistence and stability of a focal intraguild predation interaction. [ABSTRACT FROM AUTHOR]

Although the canonical concept of intraguild predation evokes images of predators and prey, several subdisciplines within ecology have developed theory not specifically framed in terms of predation and competition and often using system-specific terminology, yet functionally quite similar. Here, we formulate models combining exploitation and competition in predator-prey, host-parasitoid, and host-pathogen communities to compare dynamics, food web structure, and coexistence criteria for these disparate communities. Although dynamic stability in the coexistence region varies strongly among systems, in all cases coexistence of two consumers on a single resource occurs only if the intraguild prey species is more efficient than the intraguild predator at suppressing the abundance of the basal resource, and if the intraguild predator accrues a sufficient gain from attacking the intraguild prey. In addition, equilibrial abundances of all species in all three formulations respond similarly to increases in productivity of the basal resource. Our understanding of predator-prey and parasitoid-host communities has benefited from explicit examination of intraguild predation (IGP) theory, and we suggest that future research examining pathogen communities, in particular, will benefit substantially from explicit recognition of predictions from IGP theory. [ABSTRACT FROM AUTHOR]

Predation can be intense, creating strong direct and indirect effects throughout food webs. In addition, ecologists increasingly recognize that fluxes of organisms across ecosystem boundaries can have major consequences for community dynamics. Species with complex life histories often shift habitats during their life cycles and provide potent conduits coupling ecosystems. Thus, local interactions that affect predator abundance in one ecosystem (for example a larval habitat) may have reverberating effects in another (for example an adult habitat). Here we show that fish indirectly facilitate terrestrial plant reproduction through cascading trophic interactions across ecosystem boundaries. Fish reduce larval dragonfly abundances in ponds, leading to fewer adult dragonflies nearby. Adult dragonflies consume insect pollinators and alter their foraging behaviour. As a result, plants near ponds with fish receive more pollinator visits and are less pollen limited than plants near fish-free ponds. Our results confirm that strong species interactions can reverberate across ecosystems, and emphasize the importance of landscape-level processes in driving local species interactions. [ABSTRACT FROM AUTHOR]

This review discusses the interface between two of the most important types of interactions between species, interspecific competition and predation. Predation has been claimed to increase, decrease, or have little effect on, the strength, impact or importance of interspecific competition. There is confusion about both the meaning of these terms and the likelihood of, and conditions required for, each of these outcomes. In this article we distinguish among three measures of the influence of predation on competitive outcomes: short-term per capita consumption or growth rates, long-term changes in density, and the probability of competitive coexistence. We then outline various theoretical mechanisms that can lead to qualitatively distinct effects of predators. The qualitative effect of predators can depend both on the mechanism of competition and on the definition of competitive strength/impact. In assessing the empirical literature, we ask: (1) What definitions of competitive strength/impact have been assumed? (2) Does strong evidence exist to support one or more of the possible mechanisms that can produce a given outcome? (3) Do biases in the choice of organism or manipulation exist, and are they likely to have influenced the conclusions reached? We conclude by discussing several unanswered questions, and espouse a stronger interchange between empirical and theoretical approaches to this important question. [ABSTRACT FROM AUTHOR]

Much of the focus in evolutionary biology has been on the adaptive differentiation among organisms. It is equally important to understand the processes that result in similarities of structure among systems. Here, we discuss examples of similarities occurring at different ecological scales, from predator–prey relations (attack rates and handling times) through communities (food-web structures) to ecosystem properties. Selection among systemic configurations or patterns that differ in their intrinsic stability should lead generally to increased representation of relatively stable structures. Such nonadaptive, but selective processes that shape ecological communities offer an enticing mechanism for generating widely observed similarities, and have sparked new interest in stability properties. This nonadaptive systemic selection operates not in opposition to, but in parallel with, adaptive evolution. [ABSTRACT FROM AUTHOR]

Predator-prey interactions are ubiquitous and powerful forces that structure ecological communities. 1–3 Habitat complexity has been shown to be particularly important in regulating the strength of predator-prey interactions. 4–6 While it is well established that changes in habitat structure can alter the efficacy of predatory and anti-predatory behaviors, 7–9 little is known about the consequences of engineering activity by prey species who modify the external environment to reduce their own predation risk. Using field surveys and manipulative experiments, we evaluated how habitat modification by Brandt's voles (Lasiopodomys brandtii) influences predation risk from a principal avian predator (shrike; Lanius spp.) in a steppe grassland, located in Inner Mongolia, China. We found that voles actively modify habitat structure by cutting down a large, unpalatable bunchgrass species (Achnatherum splendens) in the presence of shrikes, a behavior that disappeared when these avian predators were excluded experimentally. The damage activities of these voless dramatically decreased the volume of unpalatable grasses, which in turn reduced visitations by shrikes and thus mortality rates. Our study shows that herbivorous prey that act as ecosystem engineers can directly reduce their own predation risk by modifying habitat structure. Given the ubiquity of predation risks faced by consumers, and the likely ability of many consumers to alter the habitat structure in which they live, the interplay between predation risk and ecosystem engineering may be an important but unappreciated mechanism at play in natural communities. [Display omitted] • Voles modified habitat structure by destroying a large, unpalatable bunchgrass • Damage activities of voles decreased the plant volume of the bunchgrasses • Vole damage activities were enhanced at the presence of the predatory birds • Habitat modifications by voles reduced predation risk and increased vole survival Zhong et al. show that by damaging a large, unpalatable bunch grass, Brandt's voles in steppe grasslands in China can reduce the predation risk from avian predators (Lanius spp.) probably due to improved vision. Habitat modifications by voles can reduce the visiting frequency of avian predators and thus increase the survival of voles. [ABSTRACT FROM AUTHOR]