Daily Patterns of Optimal Producer and Scrounger Use under Predation Hazard: A State-Dependent Dynamic Game Analysis.

Feeding in groups often gives rise to joining: feeding from other's discoveries. The joining decision has been modeled as a producer-scrounger game where the producer strategy consists of searching for one's food and the scrounger strategy consists of searching for food discovered by others. Previous models revealed that the evolutionarily stable proportion of scrounging mostly depends on the fraction of each food patch available only to its producer. These early models are static and state independent and are therefore unable to explore whether the time of day, the animal's state, and the degree of predation hazard influence an individual's decision of whether to use the producer or scrounger strategy. To investigate these issues, we developed a state-dependent dynamic producer-scrounger game model. The model predicts that, early in the day, low reserves promote a preference for the scrounger strategy, while the same condition late in the day favors the use of the producer strategy. Under rich and clumped food, the availability of scrounging can improve the daily survival of any average group member. The model suggests only weak effects of predation hazard on the use of scrounging. Future developments should consider the effects of dominance asymmetries and allowing foragers a choice between foraging alone or in a group harboring an evolutionarily stable frequency of scrounger.