On the evolution of delayed recruitment to food bonanzas

Abstract

Whereas food sharing by immediate recruitment to food bonanzas is relatively common, especially among birds, delayed recruitment from overnight roosts is comparatively rare, although it has been studied extensively in the common raven (Corvus corax). Two hypotheses have been advanced to explain the evolution of delayed recruitment. Under the status-enhancement hypothesis, delayed recruiting is favored because the recruiter's social status increases with the number of followers it leads to a food source. The posse hypothesis also focuses on the number of individuals recruited to a site, but in this case aggregation is favored because larger groups are more likely to usurp a carcass defended by a pair of territorial adult ravens. We used a game-theoretic model to explore the logic of immediate versus delayed recruitment in the light of these hypotheses. In particular, we identified three critical values of the probability of immediate recruitment: that below which delayed recruitment is a cooperative strategy, that below which delayed recruitment is an evolutionarily stable strategy, and that below which a mutant strategy of delayed recruitment will invade a population of immediate recruiters to reach fixation. The model demonstrates that either status enhancement or the posse effect may alone suffice for the evolution of delayed recruitment to food bonanzas via mutualistic information sharing at communal roosts.