Foraging on Patches: Are Groups Disadvantaged?

Abstract

Valone (1993) describes the predictions of a mathematical model representing foraging for food which is distributed unevenly between patches. The reward rate from a patch is probabilistic and declines as the patch is exploited. Hence, it is optimal for foragers to elect to leave a patch when some criterion relating to the reward rate is triggered, rather than remain until the patch is absolutely exhausted. Valone compares the performance of the solitary forager to a cohesive group of foragers which leave together either when any individual elects to leave or when a designated leader elects to leave. He observed that (whichever leaving strategy was used) the average uptake of the group foragers was always lower than that of an individual foraging alone. Whilst sharing information between group members was seen to reduce the disadvantage, foragers never benefited from being in a cohesive group. Hence Valone's work seems to agree with Hutto's (1988) suggestion that the overriding importance of group cohesion (for reasons other than foraging) can result in a sacrifice in individual foraging efficiency. Here, I investigate whether Valone' s conclusion about the cost of group cohesion is sensitive to model assumptions and in particular to the criterion used in departure decisions.