Individuals in natural populations encounter each other in numerous different ways. Such encounters include mating, conflicts over food or other resources, or the joint and co-operative acquiring of resources. The behavioral adaptations to such situations are often studied by evolutionary game theory. In this chapter, we will review some classic behavioral games: the Hawk–Dove, the Prisoner's Dilemma (including the evolution of co-operation), and the somewhat more obscure Rock–Scissors–Paper game. We also extend those problems to spatially heterogeneous environments. Towards the end of this chapter, we will combine the game theoretical analyses with dispersal-coupled population models.

Many, but far from all, encounters between individuals are pairwise. If the encounter involves a conflict, there is generally a winner and a loser. Take, e.g., two male deer fighting for the chance of mating with a female. The fight may be furious and last for a long time, possibly resulting in injuries to one or both contestants. Eventually one of the males will retreat and the winner will gain the mating. Such behavioral and ecological problems have inspired the development of evolutionary game theory (Maynard Smith and Price 1973; Maynard Smith 1982).

Most evolutionary theory assumes selfishness-driven adaptations (Dawkins 1976). It does not pay an individual to be nice or altruistic and helpful towards others unless there is a guarantee for not being cheated. Hence, altruistic behaviors are susceptible to selfish cheaters and will disappear from the population.