Assortment at different cost-benefit ratios and different frequencies of cooperators. Blue areas indicate high positive assortment and red values indicate low positive assortment between cooperators. (a, b, c) Scenarios without selection (s = 0). (d, e, f) Matching scenarios with selection (s = 0.5). (g, h, i) Differences in assortment between scenarios with and without selection. (a), (d), (g) Baseline scenario, maximal group size n
= 10, individual migration rate m = 0.02. (b, e, h) Increased migration rate (n
= 10, m = 0.05). (c, f, i) Decreased group size (n
= 5, m = 0.02).