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The availability of food has wide-ranging effects on the population size and demography of wild birds. This chapter describes methods used to discover what birds eat, to measure the rate at which they can ingest food, and the factors that affect these. Methods used to determine the composition of the diet are presented and compared. The measurement of the size and quality of prey items is described. Techniques used to measure food intake rates, prey handling time, time budgets, depletion of food supplies, and interference among foraging birds are considered.

This chapter discusses the emergence of a positive feedback between the density of predators and the availability of its food, mediated through biomass overcompensation in the prey life history stage that it forages on. This positive feedback between predation, prey availability, and thus predator population growth rate manifests itself at the population-level as an Allee effect for the predator: a predator population at low density will decline to extinction, whereas at high densities predators will manage to establish themselves in a community with prey. However, this positive relation between predator density and its population growth rate does not result from any positively density-dependent interactions among the predators themselves, which generally form the basis of an Allee effect. Instead, predators only interact with each other through exploitative competition for prey. The Allee effect emerges solely as a consequence of the demographic changes in the prey population, which are induced by the mortality that the predator imposes. For this reason this phenomenon is referred to as an “emergent Allee effect.”

This chapter discusses mixed interactions from a different perspective, taking as its point of departure the models for a structured prey, structured predator community with exclusive resources for both prey and predator that were analyzed in Chapter 6. For both the stage-structured biomass model and the size-structured model based on Kooijman–Metz energetics discussed in Chapter 6, it investigates how an increasing resource overlap between predators and consumers will change community structure and dynamics. The end point of such increasing resource overlap is a model in which consumers and predators compete for the same shared resource and adult predators feed partially or exclusively on juvenile, small-size consumers. This end point is close to the models analyzed by van de Wolfshaar, de Roos, and Persson (2006) and Hin, Schellekens, et al. (2011); the results will be discussed in the light of those publications.

In order to appreciate fully the advantages of the inertial view of population growth, it is necessary to discuss some of the details of and debates about the predator-prey account of population cycles. This chapter argues that the ratio-dependant idealization of the predator-prey interaction is quite different from the more traditional prey-dependent idealization. Moreover, the former view is not conducive to cyclic behavior.

Members of a different species may be enemies, such as predators and parasites, or friends, such as mutualists. The linked evolutionary dynamics of strongly interacting species can be complex, and are important in understanding the evolution of disease. This chapter's first section is called Rivals and talks about the social environment; mutual modification; and social coevolution. The second section, Partners, describes the Transmission Hypothesis. It also gives a novel protist-bacterium partnership and talks about experimental evolution of cooperation in a bacterium-phage system; coevolution of bacteria; plasmids; quora and consortia; and finally offers a symbiosis. The third section called Enemies details serial passage; genetic specificity; anisomorphic social matrices; the cost of virulence and resistance; evolution of virulence; epidemics; and talks about arms cycles and arms races; phage wars; and finally perpetual evolution. The final section in this chapter is about ecosystems and talks about uqba; the evolution of trophic structure through sorting; evolutionarily Stable Webs; evolved webs; the innate immune system; the acquired immune system; selection at the ecosystem level; and finally evolution and whole-system properties.

How do diverse species coexist in the complex networks of prey-predator interactions in nature? While most theoretical models predict that complex food webs do not persist, recent empirical studies have revealed the very complex structure of natural food webs. This discrepancy between theory and observation implies that essential factors stabilizing natural food webs are lacking from previous models. This chapter reviews these studies on food web complexity and its community-level consequences. It contends that the architectural flexibility arising from foraging adaptation of consumer species is key to explaining linkage patterns and persistent mechanisms of complex food webs. A novel hypothesis is presented, which relates the complexity-stability relationship to evolutionarily history of the community.

Studies on lakes provide some of the most complete investigations on the structure, dynamics, and energetics of food webs encompassing organisms from bacteria to vertebrates. The life cycle of organisms in temperate lakes is adapted to a highly seasonal environment. Food web interactions in these lakes depend on the seasonal overlap of the occurrence of potential prey, competitor, or predator species. This seasonal overlap (i.e., the match-mismatch of food web interactions) depends strongly on the seasonal dynamics of the physical environment of lakes, such as temperature, light availability, and mixing intensity. Consequently, climate variability influences food web interactions and hence the structure, dynamics, and energetics of lake food webs. This chapter provides examples and discusses the importance of seasonality for the understanding of various aspects of lake food webs and the impact of climate variability thereon.

This chapter presents size-based analyses of aquatic food webs, where body size rather than species identity is the principle descriptor of an individual's role in the food web, provides insights into food web structure and function that complement, and extends those from species-based analyses. Focus is given to body size because it underpins predator-prey interactions and dictates how the biological properties of individuals change with size. Thus, size-based food web analyses offer an approach for integrating community and ecosystem ecology with energetic and metabolic theory.

This chapter discusses adaptive diversification due to predator–prey interactions. It has long been recognized that consumption, that is, predation, can not only exert strong selection pressure on the consumer, but also on the consumed species. However, predation has traditionally received much less attention than competition as a cause for the origin and maintenance of diversity. By using adaptive dynamics theory as well as individual-based models, the chapter then illustrates that adaptive diversification in prey species due to frequency-dependent predator–prey interactions is a theoretically plausible scenario. It also describes conditions for diversification due to predator–prey interactions in classical Lotka–Volterra models, which requires analysis of coevolutionary dynamics between two interacting species, and hence of adaptive dynamics in two-dimensional phenotype spaces.

This chapter discusses a variety of positive interactions between predators foraging on different stages of the same prey species, which all emerge owing to the biomass overcompensation that may occur in prey life history stages in response to increased mortality. These interactions include emergent facilitation of specialist predators by generalists that forage on the same prey individuals as the specialists, but in addition forage on smaller or larger prey individuals as well. Furthermore, the chapter shows that two predators that specialize on different life-history stages of prey can facilitate each other to the extent that one predator relies on the presence of the other for its persistence. A stage-specific predator may act as a catalyst species, which promotes and in fact is necessary for the invasion of another predator species, but is subsequently outcompeted by the latter.

Predators that rely on surprise may be persuaded to desist from attacking if prey use reliable signals that the predator has been detected. Prey may also be able to reliably signal to a predator that they are difficult to catch or subdue, and that cause the predator to desist from attacking or switch their attack to another prey individual. The theory underlying such signals is considered and compared to the available empirical data to determine the evolution of such signals and their ecological prevalence.

Trinidadian guppies provided one of the first experimental demonstrations that predators have a significant impact on behaviour and morphology. This chapter begins with a brief general introduction to predator prey interactions. The consequences of variation in predation risk for Trinidadian guppies, and the trade-offs linked to effective predator defences are then evaluated. It asks if and when adaptive differences can be classed as evolutionary change, and considers the pitfalls associated with such assumptions. Schooling behaviour, evasive tactics, crypsis and colour patterns, mating activity, foraging, and time budgets are examined as well as the relationship between learning skills and geographic variation anti-predator responses. Age-related changes in morphology and behaviour are explored. The chapter ends by examining differences between the sexes in response to predation.

The culpeo (Pseudalopex culpaeus) and the South American grey fox or chilla (P. griseus) are closely related canids that live in western and southern South America. This chapter examines patterns of prey selection by culpeos and chillas in areas where the two species are sympatric and: (1) where sheep were abundant and the main wild prey, lagomorphs, had different densities; (2) where both canids were protected and sheep density was low. These comparisons are used to evaluate the competitive relationships between the culpeo and chilla and the factors that determine predation on livestock. The comparisons are based on two studies that reported data on culpeo and chilla food habits and a broad array of prey availability, and on unpublished information from one of these studies.

Although much of the attention to the trophic dynamics of communities is theoretical, empirical data on the different types of dynamics and the underlying mechanisms are increasingly reported. The dynamics of small food web modules, or simple webs, are compared with those of complex interactions. Food web modules are described as small systems that possess explicit dynamics. They can be seen as building blocks to construct more realistic food webs, which are subsets of the true complexity in trophic interactions in real ecosystems. It has been stated that in small food webs oscillating consumer-resource interactions occur in natural systems and that in chains of three or more levels trophic cascades seem to be important. Finally, new studies on the dynamics of complex interaction webs are mentioned, focusing on the consequences of specific patterning of interaction strengths across the web for the stability of the overall system.

This chapter focuses on renewable resources and studies the interaction of economic agents, extracting renewable resources, and the resource dynamics as well as the fate of the resources in the long run. The chapter is organized as follows. Section 15.2 introduces the model and various specifications of the model as well as two theorems. The theorems reveal the relation between zero horizon optimization where the discount rate tends to infinity, and infinite time horizon optimization, where the discount rate is finite. In Section 15.3, analytical results for the open access regime — in the literature typically viewed as a zero horizon optimization problem — are gathered concerning the systems of predator-prey and competitive interactions. Both interactions allow for limit cycles in the optimal trajectories. Section 15.4 presents numerical results for the monopoly problem.

Small springbok lambs were killed more frequently than expected and large lambs and subadults in more or less expected proportions. Adults were killed less frequently than expected, although old animals, females in late pregnancy, and males were vulnerable. A similar selection process was observed in steenbok, except medium-sized lambs, not small lambs, were usually killed, and there was no selection for sex. Cheetah predation was found to have an important density-dependent regulatory role on these two species. Analyses of prey preference using Jacob’s index showed that springbok were the most preferred species, although their distribution was limited, and springhares the most important avoided species, despite their prevalence in solitary cheetahs’ kills. Examples of diet flexibility in the cheetah occurred during an eland influx into the study area, when coalition males killed a number of calves, and when an emaciated female took to preying on unpalatable bat-eared foxes.

This chapter considers specific process involved in the experience of modern slavery and the relationship of consciousnesses that was established in it. It does so by going back to the starting point: the moment of pursuit that precedes the capture. The guiding question is how a political subjectivity can be constituted in a situation where one is a prey. How, in such a practical configuration, can one become a subject, and what kind of subject? How, being shaped by the hunting relationship, can a hunted consciousness transcend its status as prey and begin a movement of liberation? Slaveholding domination does not arise from an open struggle but rather from a relationship, which is dissymmetrical from the outset, of manhunting. Here, even before operations begin, the hunter is already in a position to be the master. The prey, taken by surprise, is not in a position to confront a group of hunters.

This chapter describes methods of diet analysis, including the major inaccuracies resulting from faecal analyses. The food composition of all species is discussed in some detail, including food intake in weight and calories. All species are fish eaters, and for most fishes are the dominant prey. Exceptions are the sea otter and the clawless/small-clawed species, taking mostly invertebrates (large crustaceans); the sea otter, predominantly sea urchins and molluscs. Fish species taken are often slow, bottom-living ones. Diets of males and females, where studied, tend to be different. There are differences in diets between otter species, noticeable especially when several are sympatric. Most species consume a daily amount of 15-20% of their body weight, the sea otter 20-30%.

This chapter discusses some of the ongoing theoretical debates on the role weasels play in community dynamics. There is a conspicuous difference between the far north, where weasels alone can continue to hunt rodents under the snow all winter long, and the temperate regions, where they are merely one component of a community of predators. Weasels have long been suspected of driving the northern rodent cycles, by extending the periods of low numbers but not preventing the peaks. By contrast, weasels further south are more like passengers than drivers, following the fluctuations in numbers of rodents that are controlled by other factors. Many carefully planned field experiments have not yet decisively proved how far weasel predation explains that difference. In temperate forests, the extent of weasel predation on birds' nests is correlated with the numbers of rodents available, and is often worst after a heavy crop of tree seeds.