Risk and interaction aversion: screening mechanisms in the Prisoner's Dilemma game

TL;DR

This paper investigates how risk-averse agents and landscape heterogeneity can promote cooperation in the Prisoner's Dilemma, revealing complex interactions that influence the coexistence of strategies and the conditions for cooperation.

Contribution

It introduces and analyzes the combined effects of risk-averse agents and site dilution as screening mechanisms that enhance cooperation in the Prisoner's Dilemma game.

Findings

Presence of risk-averse agents sustains coexistence of cooperators and defectors.

Heterogeneous landscapes with inactive sites increase cooperation levels.

Explosive increase in cooperation range near percolation threshold, with loners extinct.

Abstract

When the interactions between cooperators (C) and defectors (D) can be partially avoided within a population, there may be an overall enhancement of cooperation. One example of such screening mechanism occurs in the presence of risk-averse agents (loners, L) that are neutral towards others, i.e., both L and its opponent, whatever its strategy, receive the same payoff. Their presence in the Prisoner's Dilemma (PD) game sustains the coexistence of cooperators and defectors far beyond the level attained in their absence. Another screening mechanism is a heterogeneous landscape obtained, for example, by site diluting the lattice. In this case, cooperation is enhanced with some fraction of such inactive, interaction-averse sites. By considering the interplay of both mechanisms, we show that there is an explosive increase in the range of densities, just above the percolation threshold, where neutrality is prevented and loners become extinct, the behavior reverting to the pure PD game. Interestingly, this occurs despite defectors being usually abundant in that region. This has to be compared with the corresponding loner-free region in the undiluted case that, besides being very small, is dominatedby cooperators.