Impact of bridging social capital on the tragedy of the commons: experimental evidence

Sharing resources between members of different tribes and collectives is common and well-documented. Surprisingly, little is known about factors that are conducive to building social relationships between groups. We design a common-pool resource experiment, where after harvesting, groups can send some of their harvest to augment the resource of the outgroup. We compare donations made by individuals collectively and independently of other group members, under the conditions of equal and unequal resources. We find that individuals acting as decision-makers, but not groups, donate harvests frequently even though it is payoff-reducing. We conduct an additional treatment, where each donation is matched (doubled) by an equivalent transfer of resources, making sharing between groups payoff-improving. Under matching donations, sharing between groups flourishes, but fails to prevent resource decline in most groups. Finally, our experiment reveals that members of low-endowment groups overharvest resources in expectation of donations from affluent groups, which leads to the tragedy of the commons.