The forager's dilemma: food sharing and food defense as risk-sensitive foraging options.

Département des Sciences Biologiques, Université du Québec à Montréal, Case postale 8888, Succursale Centre-Ville, Montréal, Québec H3C 3P8, Canada.
The American Naturalist (Impact Factor: 4.55). 01/2004; 162(6):768-79. DOI: 10.1086/379202
Source: PubMed

ABSTRACT Although many variants of the hawk-dove game predict the frequency at which group foraging animals should compete aggressively, none of them can explain why a large number of group foraging animals share food clumps without any overt aggression. One reason for this shortcoming is that hawk-dove games typically consider only a single contest, while most group foraging situations involve opponents that interact repeatedly over discovered food clumps. The present iterated hawk-dove game predicts that in situations that are analogous to a prisoner's dilemma, animals should share the resources without aggression, provided that the number of simultaneously available food clumps is sufficiently large and the number of competitors is relatively small. However, given that the expected gain of an aggressive animal is more variable than the gain expected by nonaggressive individuals, the predicted effect of the number of food items in a clump-clump richness-depends on whether only the mean or both the mean and variability associated with payoffs are considered. More precisely, the deterministic game predicts that aggression should increase with clump richness, whereas the stochastic risk-sensitive game predicts that the frequency of encounters resulting in aggression should peak at intermediate clump richnesses or decrease with increasing clump richness if animals show sensitivity to the variance or coefficient of variation, respectively.

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    ABSTRACT: In many species, the intake rate of foraging individuals is negatively related to forager density due to agonistic interactions among foragers. Recently a variety of game theory models has been developed to address the question how such interference behaviour is shaped by nat- ural selection. These modelling approaches have not yet led to a com- prehensive understanding of interference competition; models that appear to be very similar yield strikingly different predictions regarding the evolutionary stability of various interference strategies. Here we attempt to unify approaches. To avoid model inconsistencies, we plead for a systematic, event-based description of the foraging process, the explicit account of feedback effects and the systematic derivation of a payoff function. To analyze the resulting evolutionary game, we use techniques from Adaptive Dynamics theory, since classical ESS tech- niques can be highly misleading when applied to the payoff functions resulting from interference competition. By means of this unified approach, we show that foraging animals can generally be expected to make their aggressive behaviour dependent on the role they play in interactions, that alternative evolutionarily stable interference strategies may evolve at the same ecological conditions, and that interference effects on intake rate cannot be taken for granted as the logical outcome of evolution. By critically discussing the setup, the assumptions and the way of analysis of some evolutionary models of interference competi- tion, we identify crucial assumptions and potential pitfalls in modelling the evolution of interference behaviour, and we demonstrate that the discrepancies between earlier model predictions often reflect seemingly subtle differences in the assumptions on behavioural flexibility.
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