Introduction

Explanations for the evolution of primate social groups and interspecific associations have invoked phylogenetic history and selective pressures exerted by predation and habitat upon individual fitness (e.g. Crook and Gartlan, 1966; Struhsaker, 1969, 1981; Wrangham, 1987; Gautier-Hion, 1988). The problem has been debated as to whether predation or foraging advantages exclusively shaped primate social systems (Wrangham, 1980; Van Schaik, 1983). Such a dichotomy is too simple, however, as shown by the great variation in primate behavioral ecology described over the past 30 years (e.g. Hall, 1965; Struhsaker, 1969; Van Schaik and Van Hooff, 1983; Wrangham, 1987). It is now generally accepted that primate social associations are formed and maintained in response to numerous interacting variables, most of which are not mutually exclusive in their effect. The challenge is to understand more fully how each factor contributes to the variation observed in nature. This chapter considers two related issues, that of intraspecific and interspecific associations in African monkeys. Monkeys apparently associate for various reasons, including reproduction, foraging advantages, resource defense, predator avoidance, and hygiene (grooming). Any of these potential advantages may be realized in both intra- and interspecific associations (the latter involving occasional hybridization; Struhsaker et al., 1988). Here, I examine how the abundance of a major predator, the crowned hawk-eagle (Stephanoaetus coronatus), and gross habitat quality correlate with the frequency of polyspecific associations, the abundance of solitary monkeys, social group size, adult sex ratios within social groups, and terrestriality of African forest monkeys.