Behavioral Ecology Advance Access published online on May 16, 2008
Behavioral Ecology, doi:10.1093/beheco/arn050
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Optimal individual positions within animal groups
a Institute of Integrative and Comparative Biology, Faculty of Biological Sciences, LC Miall Building, University of Leeds, Leeds LS2 9JT, UK b Department of Biology, State University of New York at Potsdam, Potsdam, New York 13676, USA
Address correspondence to L.J. Morrell. E-mail: L.J.Morrell{at}leeds.ac.uk.
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Abstract |
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Animal groups are highly variable in their spatial structure, and individual fitness is strongly associated with the spatial position of an animal within a group. Predation risk and food gains are often higher at the group peripheries; thus, animals must trade-off predation costs and foraging benefits when choosing a position. Assuming this is the case, we first use simulation models to demonstrate how predation risk and food gains differ for different positions within a group. Second, we use the patterns from the simulation to develop a novel model of the trade-off between the costs and the benefits of occupying different positions and predict the optimal location for an animal in a group. A variety of testable patterns emerge. As expected, increasing levels of satiation and vulnerability to predators and increasing predation risk result in increased preferences for central positions, likely to lead to increased competition or more tightly packed groups. As food availability increases, individuals should first prefer center positions, then edge, and returning to central positions under highest food levels. Increasing group size and/or density lead to more uniform preferences across individuals. Finally, we predict some situations where individuals differing in satiation and vulnerability prefer a range of different locations and other situations where there is an abrupt dichotomy between central and edge positions, dependent on the levels of monopolization of food by peripheral individuals. We discuss the implications of our findings for the structure of groups and the levels of competition within them and make suggestions for empirical tests.
Key words: competition, group living, group structure, optimization, simulation model.
Received 5 October 2007; revised 7 April 2008; accepted 9 April 2008.