When the interactions between cooperators (C) and defectors (D) can bepartially avoided within a population, there may be an overall enhancement ofcooperation. One example of such screening mechanism occurs in the presence ofrisk-averse agents (loners, L) that are neutral towards others, i.e., both Land its opponent, whatever its strategy, receive the same payoff. Theirpresence in the Prisoner's Dilemma (PD) game sustains the coexistence ofcooperators 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 somefraction of such inactive, interaction-averse sites. By considering theinterplay of both mechanisms, we show that there is an explosive increase inthe range of densities, just above the percolation threshold, where neutralityis prevented and loners become extinct, the behavior reverting to the pure PDgame. Interestingly, this occurs despite defectors being usually abundant inthat region. This has to be compared with the corresponding loner-free regionin the undiluted case that, besides being very small, is dominatedbycooperators.
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