Pool expulsion and cooperation in the spatial public goods game

Abstract

We study the evolution of cooperation in the spatial public goods game with cooperation, defection, and pool expulsion as the three competing strategies. Using the Monte Carlo method, we show that the evolution of pool expulsion and cooperation can be maintained even if the synergistic effects are not high enough to sustain cooperation based on spatial reciprocity alone, and even if the cost of pool expulsion is not negligible. Interestingly, pool expellers are protected against, or even prevail over, defectors as a result of spatial pattern formation, by means of which vacant sites form an active layer around them. Moreover, we observe continuous and discontinuous phase transitions between frozen coexistence, stationary coexistence, absorbing states, and oscillatory states in the phase diagrams. Our results indicate that pool expulsion might play an important role in the resolution of social dilemmas that unfold in groups.