DYNAMICALLY STABLE MULTIPLE STRATEGY STATES OF THE ITERATED PRISONERS-DILEMMA

We study an Iterated Prisoner's Dilemma game in which players are posi tioned on a lattice and interact with their near neighbours. Periodica lly the strategy at every site is replaced by the most successful one of its neighbours and itself. We search for collective behaviour acid find dynamically stable ''communities'' with three or even four distin ct strategies coexisting. Multi-strategy ''communities'' are more immu ne to invasion by other strategies than are homogeneous states of the individual members. An explanation of this phenomenon is provided.