Optimal aggression in kleptoparasitic interactions

Abstract

We have created and analyzed a model for kleptoparasitic interactions when individuals decide on the level of aggression in which they want to engage in the contest over a resource item. The more aggressive each individual is relative to an opponent, the higher are the chances of winning the item, but also the higher is the cost of the interaction for that individual. We consider a general class of cost functions and show that for any parameter values, i.e., for any maximal potential level of aggression of the individuals, any value of the resource and any type of the cost function, there is always a unique Nash equilibrium. We identify four possible kinds of Nash equilibria and give precise conditions for when they occur. We find that nonaggressive behavior is not a Nash equilibrium even when the cost function is such that aggressive behavior yields lower payoffs than avoiding the conflict altogether.