Fig. 2.

Cooperation frequency and rank changes by round and treatment. (a) Observed cooperation levels are higher and more stable with respect to previous PGG that did not include conflicts and/or hierarchical structures. (b) The larger the number of rank changes is, the less the established hierarchy can be considered as stable. As the number of rank changes decreases with time, we find that hierarchies are more stable in larger groups than in smaller ones. Error bars represent the Standard Error of the Mean (SEM) considering each group as an independent observation.