Differences of mean pay-offs of cooperators and defectors at different cost-benefit ratios and different frequencies of cooperators. In blue areas cooperators receive greater average pay-offs and in red areas defectors receive greater average pay-offs. (a, b, c) Scenarios without selection (s = 0). (d, e, f) Matching scenarios with selection (s = 0.5). (a, d) Baseline scenario, maximal group size n
= 10, individual migration rate m = 0.02. (b, e) Increased migration rate (n
= 10, m = 0.05). (c, f) Decreased group size (n
= 5, m = 0.02).