Received: 1 February 2018 Revised: 18 July 2018 Accepted: 6 August 2018 DOI: 10.1002/evan.21721 REVIEW ARTICLE Variation in the social organization of gorillas: Life history and socioecological perspectives Martha M. Robbins | Andrew M. Robbins Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany Abstract Correspondence A focus of socioecological research is to understand how ecological, social, and life history factors Martha M. Robbins, Max Planck Institute for influence the variability of social organization within and between species. The genus Gorilla Evolutionary Anthropology, Deutscher Platz exhibits variability in social organization with western gorilla groups being almost exclusively one- 6, 04103 Leipzig, Germany. Email:
[email protected] male, yet approximately 40% of mountain gorilla groups are multimale. We review five ultimate Funding information causes for the variability in social organization within and among gorilla populations: human dis- Max Planck Society turbance, ecological constraints on group size, risk of infanticide, life history patterns, and popula- tion density. We find the most evidence for the ecological constraints and life history hypotheses, but an over-riding explanation remains elusive. The variability may hinge on variation in female dispersal patterns, as females seek a group of optimal size and with a good protector male. Our review illustrates the challenges of understanding why the social organization of closely related species may deviate from predictions based on socioecological and life history theory. KEYWORDS dispersal, infanticide, male, male philopatry, multimale groups, relatedness 1 | INTRODUCTION to understand variability in within-species and between-species grouping patterns researchers should consider how feeding competi- Some of the earliest comparative analyses seeking to understand vari- tion and predation interact with variation in reproductive strategies ability in primate social organization focused on the occurrence of the and life history parameters of both sexes.