Santos, F. P. | Search bioRxiv

bioRxiv2024

Power asymmetry destabilizes reciprocal cooperation in social dilemmas

Direct reciprocity has been long identified as a mechanism to enhance cooperation in social dilemmas. While most research on reciprocal cooperation has focused on symmetrical interactions, real world interactions often involve differences in power. Verbal theories have either claimed that power differences enhance or destabilize cooperation, indicating the need for a comprehensive theoretical model of how power asymmetries affect direct reciprocity. Here, we investigate the relationship between power and cooperation in two frequently studied social dilemmas, the prisoners dilemma (PD) and the snowdrift game (SD). Combining evolutionary game theory and agent-based models, we demonstrate that power asymmetries are detrimental to the evolution of cooperation. Strategies that are contingent on power within an interaction provide a selective advantage in the iterated SD, but not in the iterated PD. In both games, the rate of cooperation declines as power asymmetry increases, indicating that a more egalitarian distribution of the benefits of cooperation is the prerequisite for reciprocal cooperation to evolve and be maintained.

evolutionary biology↗

bioRxiv2020

Changes in group size during resource shifts reveal drivers of sociality across the tree of life

From biofilms to whale pods, organisms have repeatedly converged on sociality as a strategy to improve individual fitness. Yet, it remains challenging to identify the most important drivers--and by extension, the evolutionary mechanisms--of sociality for particular species. Here, we present a conceptual framework, literature review, and model demonstrating that the direction and magnitude of the response of group size to sudden resource shifts provides a strong indication of the underlying drivers of sociality. We catalog six functionally distinct mechanisms related to the acquisition of resources, and we model these mechanisms effects on the survival of individuals foraging in groups. We find that whether, and to what degree, optimal group size increases, decreases, or remains constant when resource abundance declines depends strongly on the dominant mechanism. Existing empirical data support our model predictions, and we demonstrate how our framework can be used to predict the dominant social benefit for particular species. Together, our framework and results show that a single easily measurable characteristic, namely, group size under different resource abundances, can illuminate the potential drivers of sociality across the tree of life.

animal behavior and cognition↗