'How many of us are there?': Group size uncertainty and social value orientations in common resource dilemmas

In two studies, we investigate the effects of group size (un)certainty and social value orientations in common resource dilemmas. By focusing on this largely unexplored type of environmental uncertainty, we show that, in contrast to the often replicated finding that resource size uncertainty leads to over-harvesting in common resource dilemmas, group size uncertainty is not necessarily detrimental to the collective interest. Furthermore, we argue and show that whereas under group size certainty people base their individual harvests on the equal division rule, under group size uncertainty they base their harvests on their own social value orientations: whereas under group size certainty both proselfs and pro-socials harvest about an equal share of the common resource, under uncertainty prosocials show self-restraint in order to further their group's outcomes.

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