Fig. 5: Snapshots of the population in the stationary state for different parameter values.
Different strategies are color codded (legend). In (a,) r1 = 1.7, r2 = 1.7, in (b,) r1 = 3.5 and r2 = 3.5, and in c, r1 = 3, and r2 = 1.8. In all the cases cg = 0.6. For small enhancement factors (a), the red queen dynamics in which cooperators only in the costly institute survive in large numbers occur. For larger enhancement factors (b), the black queen dynamics in which cooperators in both institutions survive and help each other suppress defection occur. By increasing the enhancement factors (c), non-costly cooperators dominate. However, a small frequency of costly cooperators survives and purge the population from defectors by moving along the bands of non-costly defectors. Here, individuals reproduce with a probability proportional to the exponential of their payoff with a selection parameter equal to β = 5. The population resides on a 400 × 400 square lattice with von Neumann connectivity and periodic boundaries. Parameter values: g = 5 and ν = 10−3.
