Emergence of cooperation in spatial social dilemmas with expulsion

In social dilemmas cooperators pay costs for other individuals to receive benefits, whereas defectors are the benefactors but do not provide anything in return. What is more, except in the snowdrift game, defective strategies are evolutionarily stable against invasion by cooperative strategies under strong selection. It is thus of interest to determine under which conditions the spontaneous emergence of cooperation is possible in a population consisting entirely of defectors. To that effect, we here want to concentrate on exploring how expulsion influences the emergent dynamics of cooperation in the context of the spatial social dilemmas. Interestingly, expulsion can indeed support the emergence of cooperators for all classes of social dilemma games. By analyzing the spatial expansion and invasion processes of cooperative individuals, we further reveal that merely a 1 x 2 (or 2 x 1) cluster of expulsive cooperators, introduced for example by means of mutations, is required for invading and completely dominating a spatial population of expulsive defectors provided that the cost of cooperation is no larger than a constant value. (C) 2021 Elsevier Inc. All rights reserved.