Concessions, lifetime fitness consequences, and the evolution of coalitionary behavior

Abstract

The relationship between the costs of coalitionary behavior and the evolution of such behavior has not been closely examined by theoretical studies. Here, we create a set of life-history models for species whose coalitionary behavior is genetically determined to investigate how different types of costs afflicted upon members of failed coalitions, in terms of survival, fecundity, and social rank, may influence the nature of coalitionary behavior that emerges at evolutionary equilibrium. We also extend previous theory by examining the coevolution between coalitionary behavior and concessions granted by dominant individuals to prevent dominants from being targeted by coalitions. We show that species that form coalitions to contest social rank evolve to regularly form bridging coalitions under a vast majority of social and ecological settings, whereas species that contest fecundity form all-up coalitions under most conditions. Further, dominant individuals concede resources to subordinates to prevent coalitionary attacks only in very few circumstances, and these concessions occur only to ensure another individual is a more attractive coalition target. We compare and contrast results to empirical data to provide an evolutionary context for commonly observed coalitionary behaviors in the animal kingdom.