Cooperation in social dilemmas: Volunteering in public goods games

Cooperative behavior among unrelated individuals is one of the fundamental problems in biology and social sciences. Reciprocal altruism fails to provide a solution if interactions are not repeated often enough or groups are too large. Punishment and reward can be very effective but require that defectors can be traced and identified. Here we present a simple but effective mechanism operating under full anonymity. Voluntary participation in public goods games can foil exploiters and overcome the social dilemma. This natural extension leads to rock-scissors-paper type cyclic dominance of the three strategies cooperate, defect and loner i.e. those unwilling to participate in the public enterprise. In voluntary public goods interactions the three strategies can co-exist under very diverse assumptions on population structure and adaptation mechanisms. In particular, spatially structured populations, where players interact only with their nearest neighbors, lead to interesting dynamical properties and intriguing spatio-temporal patterns. Variations of the value of the public good result in transitions between one-, two- and three-strategy states which are in the class of directed percolation. Although volunteering is incapable of stabilizing cooperation, it efficiently prevents successful spreading of selfish behavior and enables cooperators to persist at substantial levels.

Refreshments will be served at 2:45 p.m. in the Faculty Lounge, Math Annex (Room 1115).