Socioecology and the role of scramble competition

Andreas Berghänel, Sarah Marshall, Friederike Range

Ecological explanations for social organization and behavior are central to behavioral ecology. Unfortunately, the continuing mismatch between theoretical predictions and some empirical data led to increasingly complex hypotheses with numerous factors, raising doubts about their predictive value or even falsifiability. Moreover, several taxon-specific socioecological hypotheses have been developed that are seemingly detached from one another. We discuss how an integration of different hypotheses may help to clarify theoretical arguments and empirical discrepancies. We will first integrate two major socioecological hypotheses developed for carnivores and primates respectively, namely the Resource Dispersion Hypothesis (RDH) and the Socioecological Model (SEM). We then discuss how both hypotheses can benefit each other, particularly by implementing new perspectives about the role of scramble competition. First, the RDH proposes that under certain widespread conditions, territories provide surplus resources that can maintain stable groups without any costs and thus also without any need for direct benefits to the territory owners. We argue that such cost-free group formation requires strong within-group contest competition that assures priority of access to the territory owners, but would not withstand within-group scramble competition, which inevitably causes costs for all group members. Second, the SEM proposes that under pure within-group scramble competition, resources cannot be monopolized and thus dominance rank and social tolerance are pointless. We argue that rank-dependent eviction and group fission into territory holders and leavers as proposed by the RDH provides rank-dependent benefits and allows for social tolerance in terms of granted group membership even under pure within-group scramble competition.