Optimal Degree of Skew in Cooperative Societies

An optimization model is employed to determine the outcome ofwithin-group conflict in cooperative societies. The model assumesthat selection acts simultaneously on the stronger, dominantmembers of the group to secure more benefits for themselvesat the expense of subordinates, and on subordinates to leavethe group in response to this usurpation if they can do betterelsewhere. When it is in the interest of the dominant to maintainthe group, the dominant will be limited in its opportunity tobias the benefits in its favor by the options available to subordinatesoutside the group. The resulting differences in fitness or netpay-off among group members due to usurpation by dominants definethe degree of skew. Ecological factors affect both the net benefitof grouping and the options for leaving, and thus establishthe limits of skewing. The assumptions and rules governing thisinteraction are first outlined using a game theory approach.A continuous model for predicting the exact degree of skew isthen developed. This analysis shows that the degree of skewincreases when the benefit of group breeding relative to solitarybreeding increases, and when the degree of relatedness amonggroup members increases. Finally, the trade-offs between breedingwith relatives versus nonrelatives are analyzed from a dominantrelative's point of view. The results of two empirical studieson a social bird and a social wasp are compared to the predictionsof these models. The exceptionally good fit to the models isinterpreted as evidence in favor of the "social manipulation"approach to "helping" and "altruism" in cooperatively breedingspecies.