How socio-ecological factors influence the differentiation of social relationships: an integrated conceptual framework

The extent of differentiation of social relationships within groups is a means to assess social complexity, with greater differentiation indicating greater social complexity. Socio-ecological factors are likely to influence social complexity, but no attempt has been made to explain the differentiation of social relationships using multiple socio-ecological factors. Here, we propose a conceptual framework based on four components underlying multiple socio-ecological factors that influence the differentiation of social relationships: the extent of within-group contest competition to access resources, the extent to which individuals differ in their ability to provide a variety of services, the need for group-level cooperation and the constraints on social interactions. We use the framework to make predictions about the degree of relationship differentiation that can be expected within a group according to the cumulative contribution of multiple socio-ecological factors to each of the four components. The framework has broad applicability, since the four components are likely to be relevant to a wide range of animal taxa and to additional socio-ecological factors not explicitly dealt with here. Hence, the framework can be used as the basis for the development of novel and testable hypotheses about intra- and interspecific differences in relationship differentiation and social complexity.

Group Contest Success Function: The Heterogeneous Individuals Case

This paper extends the axiomatic characterization of the group contest success function in [Münster, J. [2009] Group contest success functions, Econ. Theory 41(2), 345–357] to groups with heterogeneous individuals (e.g., individuals with different skills or different cognitive capacities). The obtained function allows for differences in terms of effort effectiveness between the group individuals and differences in terms of returns to scale at the aggregate level.

The evolution of social bonds in primate males

Social bonds, here defined as strong, equitable and enduring social relationships, increase fitness in both male and female primates irrespective of their dispersal regime. Despite the benefits they carry for some, social bonds evolved more often among female than among male primates which is thought to be caused by the unsharable nature of males’ limiting resource, fertilizations. Here we present a structured review of variation in primate male social relationships, mating systems, and social organization. In addition to classical socio-ecological reasoning and recent models on the evolution of male coalitions, we consider the phylogenetic history of species living in multi-male groups and alternative evolutionary routes to male co-residency, which may constrain the evolution of male social bonds in some cases. We summarize our results in a conceptual framework that represents the effects of male contest competition within and between groups on male social organization, affiliation and cooperation. We conclude that male social bonds evolved as long-term alliances that gain their adaptive function in within group contests and, thus, that the evolution of male social bonds is driven by variation in within group contest competition. Between group contest competition may select for large male group size but in the end it is the narrow window of medium to low within group contest competition that promotes the evolution of political coalitions and thus is responsible for the rarity of social bonds among primate males.