Primate Social Groups as Biological Islands

Abstract

The intestinal protozoan faunas of 11 social groups of Cercocebus albigena, 3 groups of Ceropithecus mitis, 3 groups of Cercopithecus ascanius, 2 groups of rain forest and 4 groups of savannah Papio anubis are documented. All individuals in a particular social group exhibit identical protozoan faunas. All social groups of each species, except the savannah P. anubis, exhibit intergroup differences in the composition of their protozoan faunas. The number of intestinal, protozoan species in Cercocebus albigena social groups is a function of group size. The similarity between the protozoan faunas of different C. albigena groups is related to the density of the social groups and types of land tenure in particular localities. Past social history of C. albigena groups may have some influence on the level of similarity of different groups' faunas. Entrance of a nongroup member into a group of Cercopithecus mitis resulted in an increase in the species richness of the group's protozoan fauna. Group fission may result in reduction of a group's protozoan species richness. All groups of savannah Papio anubis exhibit identical protozoan faunas. I argue that this is because savannah P. anubis has a higher rate of exchange of individuals between groups than has been recorded for the rain forest primates under consideration. I hypothesize that the differing rates of exchange are due to disease—related selection against traits which result in high rates of individual exchange among rain forest primate groups. Primate social groups are functionally biological islands; the species of their protozoan faunas changes according to group size and levels of protozoan migration between groups.