Data from: Group augmentation, collective action, and territorial boundary patrols by male chimpanzees

How can collective action evolve when individuals benefit from cooperation
regardless of whether they pay its participation costs? According to one
influential perspective, collective action problems are common, especially
when groups are large, but may be solved when individuals who have more to
gain from the collective good or can produce it at low costs provide it to
others as a byproduct. Several results from a 20-y study of one of the
most striking examples of collective action in nonhuman animals,
territorial boundary patrolling by male chimpanzees, are consistent with
these ideas. Individuals were more likely to patrol when (i) they had more
to gain because they had many offspring in the group; (ii) they incurred
relatively low costs because of their high dominance rank and superior
physical condition; and (iii) the group size was relatively small.
However, several other findings were better explained by group
augmentation theory, which proposes that individuals should bear the
short-term costs of collective action even when they have little to gain
immediately if such action leads to increases in group size and long-term
increases in reproductive success. In support of this theory, (i)
individual patrolling effort was higher and less variable than
participation in intergroup aggression in other primate species; (ii)
males often patrolled when they had no offspring or maternal relatives in
the group; and (iii) the aggregate patrolling effort of the group did not
decrease with group size. We propose that group augmentation theory
deserves more consideration in research on collective action.