On the role of age and body size in risky animal contests

Abstract

The relative strength of an animal contestant usually determines its chance of victory in an escalated contest. However, when benefits enhance the reproduction of an individual and costs affect its survival (or vice versa) then behavior in these conflicts is also determined by the future reproductive success of a contestant. Aided by simple game theory models this paper will try to demonstrate, that the body size ratio of opponents is an important but not unique determinant of the outcome of a fight. Under the same size ratio, the absolute sizes of the contestants may affect the evolution stable strategy (ESS) result. Another crucial agent is the possible asymmetry in ages of individuals. Furthermore, identical pairs of rivals may behave in different ways due to unequal resource availability in different populations. These predictions remain valid both in contests where the level of escalation is controlled by opponents and those where it is not. Although the agents determining results of asymmetric contests may be complex, some helpful recomendations for field research can be put forward.