Predation has long been implicated as a major selective force in the evolution of several morphological and behavioral characteristics of animals. The importance of predation during evolutionary ti...

Behavioral decisions made under the risk of predation: a review and prospectus

Body size is manifestly one of the most important attributes of an organism from an ecological and evolutionary point of view. Size has a predominant influence on an animal's energetic requirements, its potential for resource exploitation, and its susceptibility to natural enemies. A large literature now exists on how physiological, life history, and population parameters scale with body dimensions (24, 131). The ecological literature on species interactions and the structure of animal communities also stresses the importance of body size. Differences in body size are a major means by which species avoid direct overlap in resource use (153), and size-selective predation can be a primary organizing force in some communities (20, 70). Size thus imposes important constraints on the manner in which an organism interacts with its environment and influences the strength, type, and symmetry of interactions with other species (152, 207). Paradoxically, ecologists have virtually ignored the implications of these observations for interactions among species that exhibit size-distributed populations. For instance, it has been often suggested that competing species

https://www.jstor.org/stable/pdf/2096954.pdf

The ontogenetic niche and species interactions in size-structured populations

Beginning with Emlen (1966) and MacArthur and Pianka (1966) and extending through the last ten years, several authors have sought to predict the foraging behavior of animals by means of mathematical models. These models are very similar,in that they all assume that the fitness of a foraging animal is a function of the efficiency of foraging measured in terms of some "currency" (Schoener, 1971) -usually energy- and that natural selection has resulted in animals that forage so as to maximize this fitness. As a result of these similarities, the models have become known as "optimal foraging models"; and the theory that embodies them, "optimal foraging theory." The situations to which optimal foraging theory has been applied, with the exception of a few recent studies, can be divided into the following four categories: (1) choice by an animal of which food types to eat (i.e., optimal diet); (2) choice of which patch type to feed in (i.e., optimal patch choice); (3) optimal allocation of time to different patches; and (4) optimal patterns and speed of movements. In this review we discuss each of these categories separately, dealing with both the theoretical developments and the data that permit tests of the predictions. The review is selective in the sense that we emphasize studies that either develop testable predictions or that attempt to test predictions in a precise quantitative manner. We also discuss what we see to be some of the future developments in the area of optimal foraging theory and how this theory can be related to other areas of biology. Our general conclusion is that the simple models so far formulated are supported are supported reasonably well by available data and that we are optimistic about the value both now and in the future of optimal foraging theory. We argue, however, that these simple models will requre much modification, espicially to deal with situations that either cannot easily be put into one or another of the above four categories or entail currencies more complicated that just energy.

Citation classic - optimal foraging - a selective review of theory and tests

Proponents of optimal foraging theory attempt to predict the behavior of animals while they are foraging; this theory is based on a number of assump­ tions ( 133 , 155 , 2 10, 23 1 ) . First, an individual's contribution to the next generation (i.e. its "fitness") depends on its behavior while foraging. This contribution may be measured genetically or culturally as the proportion of an individual's genes or "ideas", respectively, in the next generation. In the former case, the theory is simply an extension of Darwin's theory of evolution. Second, it is assumed that there should be a heritable component of foraging behavior, i.e. an animal that forages in a particular manner should be likely to have offspring that tend to forage in the same manner. This heritable compo­ nent can be either the actual foraging responses made by an animal or the rules by which an animal learns to make such responses. In other words, optimal foraging theory may apply regardless of whether the foraging behavior is learned or innate. Given these first two assumptions, it follows that the proportion of individuals in a population foraging in ways that enhance their fitness will tend to increase over time. Unless countervailed by sufficiently strong group selection (see 287, 242), foraging behavior will therefore evolve, and the average foraging behavior will increasingly come to be characterized by those characteristics that enhance individual fitness. The third assumption is that the relationship between foraging behavior and fitness is known. This relationship is usually referred to as the currency of fitness (23 1 ) . In general, any such currency will include a time scale, although in some cases it may be assumed that fitness is a function of some rate.

Optimal Foraging Theory: A Critical Review

We present an experiment designed to test the hypothesis that fish respond to both relative predation risk and habitat profitability in choosing habitats in which to feed. Identical populations of three size—classes of bluegill sunfish (Lepomis macrochirus) were stocked on both sides of a divided pond (29 m in diameter), and eight piscivorous largemouth bass (Micropterus salmoides) were introduced to one side. Sizes of both species were chosen such that the small class of bluegills was very vulnerable to the bass, whereas the largest class was invulnerable to bass predation. We then compared mortality, habitat use, and growth of each size—class in the presence and absence of the bass. Only the small size—class suffered significant mortality from the bass (each bass consumed on average about one small bluegill every 3.8 d); the two larger size—classes exhibited similar mortality rates on both sides of the pond. In the absence of the bass, we found that habitat use of all size—classes was similar and that the pattern of habitat use maximized foraging return rates (Werner et al. 1983). In the presence of the bass the two larger size—classes chose habitats to maximize return rates, but the small size—class obtained a greater fraction of its diet from the vegetation habitat, where foraging return rates were only one—third of those in the more open habitats. The small size—class further exhibited a significant depression in individual growth in the presence of the bass; the growth increment during the experiment was 27% less than that for small bluegills in the absence of the bass. Because of the reduced utilization of more open habitats by the small fish in the presence of bass, resources in these habitats were released to the larger size—classes, which showed greater growth in the presence of the bass than in its absence. We develop methods to predict the additional mortality expected on a cohort due to a reduction in growth rate (because individuals are spending a longer time in vunerable sizes), and discuss and potential for predation risk to enforce size—class segregation, which leads de facto to resource partitioning.

An Experimental Test of the Effects of Predation Risk on Habitat Use in Fish

Optimal foraging of sticklebacks on swarming prey

On optimal diet in a patchy environment.

Foraging on potentially harmful prey.

Two predator-prey difference equations considering delayed population growth and starvation

ACCORDING to the principle of natural selection, each individual animal is assumed to maximise its inclusive fitness1. Thus, observed behaviour patterns should result from optimisation processes involving costs and benefits measured in a currency of fitness2,3. Certain foraging strategies have been shown to maximise energy intake per unit time3–6. Maximisation of the rate of energy intake, however, is an optimal strategy only if feeding behaviour does not conflict with other needs, such as the detection of predators. If the foraging animal runs a high risk of being preyed upon, the optimal strategy may be a compromise of both needs. A predator's influence on optimal foraging has been dealt with, so far, only in a hypothetical manner3,5. We have investigated this problem experimentally using three-spined sticklebacks (Gasterosteus aculeatus) attacking a swarm of water fleas (Daphnia magna). We report here that after exposure to a model of an avian predator the sticklebacks' foraging behaviour changes such that they attack swarm regions of lower density which provide a lower feeding rate but should increase their ability to detect an approaching predator. This is predicted by a model using Pontryagin's principle of maximisation.

Influence of a predator on the optimal foraging behaviour of sticklebacks ( Gasterosteus aculeatus L.)

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