Optimal Foraging and Predator–Prey Dynamics

A system consisting of a population of predators and two types of prey is considered. The dynamics of the system is described by differential equations with controls. The controls model how predators forage on each of the two types of prey. The choice of these controls is based on the standard assumption in the theory of optimal foraging which requires that each predator maximizes the net rate of energy intake during foraging. Since this choice depends on the densities of populations involved, this allows us to link the optimal behavior of an individual with the dynamics of the whole system. Simple qualitative analysis and some simulations show the qualitative behavior of such a system. The effect of the optimal diet choice on the stability of the system is discussed.     

Optimal Foraging Theory and the Psychology of Learning

The development of optimization theory has made important contributionsto the study of animal behavior. But the optimization approachneeds to be integrated with other methods of ethology and psychology.For example, the ability to learn is an important componentof efficient foraging behavior in many species, and the psychologyof animal learning could contribute substantially to testingand extending the predictions of optimal foraging theory.     

Prediction of Switching and Counter-Switching Based on Optimal Foraging

It is shown that optimally foraging predators can switch or counter-switch depending on prey types and on environmental conditions, due to changes in the profitability of the prey types involved. Subsequently rules are developed to predict switching or counter-switching by the predator when prey densities change, using examples from the literature as well as new data on prey selection in sticklebacks.     

Optimal Foraging and Hominid Evolution: Labor and Reciprocity

We argue that cooperative foraging incorporating information exchange may have preceded tool use during the course of hominid evolution. In moving to the savanna, early hominids must have faced increasingly dispersed but sometimes more profitable food sources. The problem is finding such foods. Search costs can be reduced for each individual if a number of foragers cooperate by ranging over different parts of the habitat and by exchanging information about encountered food items. Given the probability of encountering a given food item and the return per individual for that item, it is possible to specify the optimal group size. Thus, in the patchy savanna environment, selection would have favored increased gregariousness and cooperation on the part of early hominids, setting the stage for the emergence of reciprocal exchanges of information and resources. However, such a system of reciprocity is open to manipulation. Outside the foraging context, the tension between reciprocity and manipulation would shape other social interactions. Communication and information exchange may have been more critical than labor and technology in evolving hominids from hominoids. Human sociality may find its origins in a shift in primate foraging tactics.     

Optimal phenology and body-size of Orb-weaving spiders: Foraging constrains

Summary Large orb-weaving spiders in temperate zones always mature in Autumn. A model based on laboratory feeding experiments and insect trap samples from an old-field in Michigan was used to simulate orb-weaver foraging behavior in various habitats and seasons. Seasons of peak energy return rates in habitats used by old-field orb-weavers indicate that prey availability plays a role in determining phenologies of large spiders. The minimum body-size to which the constraint applies in the model corresponds to the lower size-range of strictly Autumn-maturing orb-weaver species.     

Optimal Foraging Group Size for a Human Population: The Case of Bari Fishing

The Bari of the Maracaibo basin obtain most of the meat in theirdiet by spearfishing, usually in stretches of river which theydam off before fishing them. As the number of men in a fishingparty increases, the time to build a dam decreases in approximatelythe same way that the catch per man decreases. The decreasein catch per manhour, as more men are added to a fishing party,is thus quite shallow. The interrelationship of these variablespermits a prediction of the optimal number of men in a fishingparty, based on the principle that below a certain number ofparticipants, the addition of more men to the fishing partygains each individual more in time than it costs him in returnsper man-hour. Data so far available indicate that the optimalnumber of men in a fishing party is about the same as the averagenumber of adult men residing in a Bari longhouse.     

Home Range in a Patchy Environment: Optimal Foraging Predictions

Optimal foraging rules are used to simulate the home range ofa central place forager in an environment with a patchy resourcedistribution. The model makes the following predictions: (1)Home range size is inversely related to maximum resource densityand resource renewal rate. It is positively related to the animal'srate of movement. (2) The optimal home range shape in a patchyenvironment is elongate rather than circular, with a major tominor axisratio of about 2:1. This agrees well with observedvalues. (3) The proportion of the total home range used perforaging bout is positively related to the renewal rate of theenvironment. (4) The tendency of an animal to concentrate itsactivity in a subregion of the home range (rather than distributingits activity uniformly) will increase with the maximum resourcedensity. This tendency is measured as the ratio of the areawhich will contain 65% of the occurrences of an animal to thearea required to contain 95% of its occurrences. The valuesof the ratio predicted by this model agree closely with observedvalues.     

Optimal Foraging: Field Tests of Diet Choice and Habitat Switching

The application of optimal foraging theory to questions of predatorbehavior, and evidence bearing on the utility of this construct,are reviewed. Experimental tests of simple models predictingprey choice are examined with particular reference to the size-selectionof prey by fish. Laboratory estimates of model parameters arethen used to predict prey choice in the field and data fromseveral field tests are presented which corroborate these predictions.When parameters are habitat specific this permits predictionsof net return from foraging in different habitats and consequentlypredictions of habitat use and switching. Field data gatheredto test these predictions demonstrate that fish feed in thericher habitats and switch habitats when the profitability ofone drops below that of another. Examples are provided showinghow these models can then be used to relate behavioral and morphologicaldifferences between species and questions at higher levels suchas the nature of species interactions and community structure.It is suggested that this may be one of the more useful applicationsof optimal foraging theory. Finally, some of the criticismsof the theory and important questions requiring further studyare discussed.     

Optimal Foraging in Hummingbirds: Testing the Marginal Value Theorem

To a hummingbird, clusters of flowers on inflorescences representpatches and provide an ideal situation to test prediction ofoptimal patch-use. The basic question is what decision ruleshould a hummingbird use to decide whether or not to leave aninflorescence? The hypothesis is that hummingbirds will adoptthe decision rule that maximizes their net rate of energy gainwhile foraging. This hypothesis leads to an analogue of Charnov'smarginal value theorem which determines an optimal decisionrule. The optimal decision ruleis then used to predict aspectsof the hummingbirds' foraging, and these predictions are comparedwith field data The optimal decision rule is a function of how much informationis used by the hummingbirds. Data indicate that a decision toleave an inflorescence is a function of the number of flowersvisited, the number of flowers available on the inflorescence,and the amount of nectar obtained at the last flower. The optimaldecision rule was calculated assuming no additional informationis used.     

Optimal Foraging Theory: A Review of Some Models and Their Applications

Hunter-Gatherer Foraging Strategies: Ethnographic and Archeological Analyses . Bruce Winterhalter and Eric Alden Smith , eds. Chicago: University of Chicago Press, 1981. x + 268 pp. $18.00 (cloth), $7.50 (paper).     

Optimal Foraging Theory and the Racecar Driver: The Impact of Student-Centered Learning on Anthropological Pedagogy

This article contributes to the field of anthropological pedagogy, adding to recent articles regarding needed change in anthropology teaching methods. All have in common the practice of anthropology in the classroom. The author used the theory of optimal foraging to encourage students to operationalize human behavior. The economic benefit that students reaped warrants discussion. Students rapidly and measurably improved several areas of their lifestyle including health, finance, and home. Pursuing an anthropology degree thus becomes a personal journey.     

Intratree Variation in Fruit Production and Implications for Primate Foraging

We tested the hypothesis that fruit quantity and quality vary vertically within trees. We quantified intratree fruit production before exploitation by frugivores at different heights in 89 trees from 17 species fed on by primates in Kibale National Park, Uganda. We also conducted a pilot study to determine if the nutritional value of fruit varied within tree crowns. Depending on the species and crown size, we divided tree canopies into 2 or 3 vertical layers. In 2-layered trees, upper crowns produced fruits that were 9.6–30.1% bigger and 0.52–140 times the densities of those from lower crowns, with one exception. Among 2-layered trees, upper crowns produced a mean of 46.9 fruits/m³ (median 12.1), while lower crowns produced a mean of 14.1 fruits/m³ (median 2.5). Among 3-layered trees, upper crowns produced a mean density of 49.9 fruits/m³ (median 12.5), middle crowns a mean of 16.8 fruits/m³ (median 6.6), and lower crowns a mean of 12.8 fruits/m³ (median 1.8). Dry pulp and moisture were systematically greater per fruit in the highest compared to the lowest canopy layers (22.4% and 16.4% respectively in 2-layered trees, 49.7% and 21.8% respectively in 3-layered trees). In 1 tree of Diospyros abyssinica, a pilot nutritional study showed that upper crown ripe fruit contained 41.9% more sugar, 8.4% more crude proteins, and 1.8 times less of the potentially toxic saponin than lower crown ripe fruit, but the result needs to be verified with more individuals and species of trees. We discuss the consequences of intratree variations in fruit production with respect to competition among frugivorous primates.     

Stochastic Optimal Foraging: Tuning Intensive and Extensive Dynamics in Random Searches

Recent theoretical developments had laid down the proper mathematical means to understand how the structural complexity of search patterns may improve foraging efficiency. Under information-deprived scenarios and specific landscape configurations, Lévy walks and flights are known to lead to high search efficiencies. Based on a one-dimensional comparative analysis we show a mechanism by which, at random, a searcher can optimize the encounter with close and distant targets. The mechanism consists of combining an optimal diffusivity (optimally enhanced diffusion) with a minimal diffusion constant. In such a way the search dynamics adequately balances the tension between finding close and distant targets, while, at the same time, shifts the optimal balance towards relatively larger close-to-distant target encounter ratios. We find that introducing a multiscale set of reorientations ensures both a thorough local space exploration without oversampling and a fast spreading dynamics at the large scale. Lévy reorientation patterns account for these properties but other reorientation strategies providing similar statistical signatures can mimic or achieve comparable efficiencies. Hence, the present work unveils general mechanisms underlying efficient random search, beyond the Lévy model. Our results suggest that animals could tune key statistical movement properties (e.g. enhanced diffusivity, minimal diffusion constant) to cope with the very general problem of balancing out intensive and extensive random searching. We believe that theoretical developments to mechanistically understand stochastic search strategies, such as the one here proposed, are crucial to develop an empirically verifiable and comprehensive animal foraging theory.     

Methodological Problems in Evolutionary Biology. XI. Optimal Foraging Theory Revisited

Optimality theory, particularly optimal foraging theory (OFT), has spurned controversy over decades. I argue that the controversy results from conceptual pitfalls. The focus in this article is on pitfalls underlying the concept of constraint. Constraints in OFT models are a means to distinguish between possible and impossible behaviours. I argue that the seemingly innocuous notion of (im)possibility is tricky. It is indeed linked here with troublesome philosophical problems concerning free will. To steer away from such problems in OFT, we need to distinguish between hard and soft constraints. Such a distinction is necessarily context-dependent. This implies that OFT, to a large extent, should take the form of natural history rather than general theory.