Conflict in the neighbourhood: Models where close relatives are in direct competition

Animal movements are frequently circumscribed, especially at the time of breeding, hence it is often true that close relatives are forced into direct competition. Whereas some inhibition of aggression is expected in conflict among relatives, a higher escalation of conflict seems inevitable if the same individuals repeatedly contest resources, and if it pays a loser in one fight to behave as a subordinate in subsequent ones. This higher escalation may be incorporated into game theory by assuming that strangers not only compete for a particular resource, but also for dominant status in future contests with the same opponent. When these two opposing influences of population structure are compared in the Hawk-Dove game and the War of Attrition, it turns out that the ESS is strongly influenced by both. For populations which are highly viscous, as regards both genes and individuals, the evolutionarily stable investment in fighting is particularly sensitive to small changes in either type of viscosity. In competition, close relatives are therefore expected to switch between the behavioural extremes of altruism and selfish aggression after only minor changes of population structure.