2 - Variation in the social system of mountain gorillas: the male perspective

Summary

Introduction

A wide variety of social systems is observed across the animal kingdom. The degree of sociality and the type of social system exhibited by a species are influenced by many factors including phylogeny, physiology, ecology, life history, and behavior (Emlen & Oring, 1977; Wrangham & Rubenstein, 1986; van Hooff & van Schaik, 1992; Lee, 1994). The observed social system is the outcome of individual strategies to maximize fitness, and both inter- and intraspecific variation in social systems can be studied within this framework. Examining intraspecific social system variation improves our understanding of the flexibility in behavioral patterns of individuals, the proximate mechanisms that produce such variation, the adaptive significance of sociality, and the evolution of social structure (Lott, 1991; Lee, 1994). Currently, behavioral ecologists are no longer viewing species as having static patterns of behavior and social structure, but instead the variation in group size, age structure, sex ratio, degree of relatedness between individuals, etc. is being examined (Strier, 1994). In particular, looking at the factors that influence the number of adult males per social unit is interesting because it relates to reproductive strategies of individuals (Kappeler, 2000).

One of the greatest benefits of the long-term monitoring of several neighboring mountain gorilla groups for over 30 years is that it has enabled us to gain a good understanding of mountain gorilla socioecology and to observe the variation in their social system. Mountain gorillas feed on evenly distributed herbaceous vegetation and face low feeding competition (Watts, 1985, 1996).