Figure 4.

Equilibrium frequency of cooperators as a function of the cost of the Public Good Game (C(x)). The panels depict the results of the individual-based simulations for non-zero stable fix points (filled marks) and instable fix points (open marks). The groups are composed of 5 individuals either picked randomly from the population (a, b, c), or from the same site in the model with spatial population structure (d, e, f). In cases a, d competition occurs only between groups, in the simulations of b and e, both individuals and groups compete with each other with compulsory participation. Finally in the cases of c, f both individual and group level selection are present and participation in the group stage is voluntary. The different marks are depicted to different threshold values (●,○: T = 5; ■,□: T = 4; ♦,◊: T = 3; ▲, Δ: T = 2).