State dependent behavior and the Marginal Value Theorem

Abstract

The Marginal Value Theorem (MVT) is the dominant paradigm in predicting patch use and numerous tests support its qualitative predictions. Quantitative tests under complex foraging situations could be expected to be more variable in their support because the MVT assumes behavior maximizes only net energy-intake rate. However across a survey of 26 studies, foragers rather consistently ''erred'' in staying too long in patches. Such a consistent direction to the errors suggests that the simplifying assumptions of the MVT introduce a systematic bias rather than just imprecision. Therefore, I simulated patch use as a statedependent response to physiological state, travel cost, predation risk, prey densities, and fitness currencies other than net-rate maximization (e.g., maximizing survival, reproductive investment, or mating opportunities). State-dependent behavior consistently results in longer patch residence times than predicted by the MVT or another foraging model, the minimize /g rule, and these rules fail to closely approximate the best behavioral strategy over a wide range of conditions. Because patch residence times increase with state-dependent behavior, this also predicts mass regulation below maximum energy capacities without direct mass-specific costs. Finally, qualitative behavioral predictions from the MVT about giving-up densities in patches and the effects of travel costs are often inconsistent with state-dependent behavior. Thus in order to accurately predict patch exploitation patterns, the model highlights the need to: (1) consider predator behavior (sit-and-wait versus actively foraging); (2) identify activities that can occur simultaneously to foraging (i.e., mate search or parental care); and (3) specify the range of nutritional states likely in foraging animals. Future predictive models of patch use should explicitly consider these parameters. Key words: marginal value theorem, predation risk, foraging, patch use, stochastic dynamic programming, state-dependent behavior. [Behav Ecol 12:71-83 (2001)] O ptimal foraging theory is an important tool for increasing our understanding of animal behavior. One optimality model that has been particularly widely used is the Marginal Value Theorem (MVT), which predicts the behavior of foraging animals collecting energy within patches. Patch depletion will eventually force the animal to move. If the animal's goal is to maximize net rate of energy intake, it should leave a patch when its foraging rate drops to the overall average intake for the entire habitat (Charnov, 1976). The MVT further predicts that if an animal encounters a series of patches of varying quality, it should bias its foraging efforts such that eventually all patches are depleted to an equal prey density. The prey density at which a forager leaves a patch is known as the giving-up density, or GUD, and therefore optimal foraging should result in all exploited patches having similar GUDs.The MVT has been extensively applied and tested. Many studies have shown good qualitative support for M...

What elk, wolves and caterpillars have in common—The perfect forager theorem

“…If these predictions [10,11,17] were true, then a healthy animal secure from predation and not exposed to competition for forage resources, or other intra and inter-species interactions, occurring outside the breeding season, should always follow the MVT while foraging. The vast research that contradicts the MVT (including simulation studies [9]), suggests that the lack of biological realism of the MVT may be an insufficient explanation for animals not following the MVT model and may not account for all factors responsible for the observed deviations from the MVT.…”

“…The MVT, derived from observations of foraging behavior of Great Tits (Parus major), received support from several field studies [2][3][4][5][6][7]. Some authors [8][9][10][11], however, argued that foraging strategies other than the MVT could be used by foragers.…”

“…It was argued [10] that the reason for refuting the MVT by several studies [9,[13][14][15][16][17] is that MVT lacks biological realism.…”

Florivory as an Opportunity Benefit of Aposematism

“…Therefore, aposematic herbivores can feed freely in clear sight of their predators, such as on flowers. Foraging theory is often concerned with opportunity costs associated with different options (Winterhalder 1983;Nonacs 2001;Eccard and Liesenjohann 2014). Florivory may provide an opportunity benefit of aposematism (Stevens and Ruxton 2013) through enhanced resource collection, which is underappreciated in the understanding of the prevalence and evolution of aposematism .…”

Evolving the “Feeling” of Time Through Sensory-Motor Coordination: A Robot Based Model

“…Optimal foraging theory models assume that the experience that the animals have of the patch during time has an incremental or a decremental effect on the animal tendency to remain in the patch. These models show that some animals behave as if they made their decision on information gained while foraging [1]. Artificial autonomous agents might face similar problems: they may be required to change their behaviour because of information gained through a repeated interaction with their environment.…”