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1Animal groups are highly variable in their spatial structure, and individual fitness is 2 strongly associated with the spatial position of an animal within a group. Predation 3 risk and food gains are often higher at the group peripheries; thus, animals must trade 4 off predation costs and foraging benefits when choosing a position. Assuming this is 5 the case, we firstly use simulation models to demonstrate how predation risk and food 6 gains differ for different positions within a group. Secondly, we use the patterns from 7 the simulation to develop a novel model of the trade-off between the costs and 8 benefits of occupying different positions, and predict the optimal location for an 9 animal in a group. A variety of testable patterns emerge. As expected, increasing 10 levels of satiation and vulnerability to predators, and increasing predation risk result 11 in increased preferences for central positions, likely to lead to increased competition 12 or more tightly packed groups. As food availability increases, individuals should first 13 prefer center positions, then edge, returning to central positions under highest food 14 levels. Increasing group size and/or density lead to more uniform preferences across 15 individuals. Finally, we predict some situations where individuals differing in 16 satiation and vulnerability prefer a range of different locations, and other situations 17 where there is an abrupt dichotomy between central and edge positions, dependent on 18 the levels of monopolization of food by peripheral individuals. We discuss the 19 implications of our findings for the structure of groups and the levels of competition 20 within them, and make suggestions for empirical tests. 21 22

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