Food sharing: a model of manipulation by harassment

Most analyses of food-sharing behavior invoke complex explanations such as indirect and delayed benefits for sharing via kin selection and reciprocal altruism. However, food sharing can be a more general phenomenon accounted for by more parsimonious, mutualistic explanations. We propose a game theoretical model of a general sharing situation in which food owners share because it is in their own self-interest-they avoid high costs associated with beggar harassment. When beggars harass, owners may benefit from sharing part of the food if their consumption rate is low relative to the rate of cost accrual. Our model predicts that harassment can be a profitable strategy for beggars if they reap some direct benefits from harassing other than shared food (such as picking up scraps). Therefore, beggars may manipulate the owner's fitness payoffs in such a way as to make sharing mutualistic.