Group size variability in primates

The effects of mean troop size, diet, territoriality, and habitat upon temporal variability of group size in primates were investigated using variance functions relating mean group size and temporal variability. Two different types of variability were described: (1) within group variability where a single troop was followed over a given period of time; and (2) between group variability where the author(s) did not distinguish one troop from the other. In the second category, CV (SD/mean) as an index of temporal group size variability proved to be dependent on mean group size among the Cercopithecidae. Large groups are more unstable in size than small ones. In the Cebidae, variability was independent of mean group size and therefore large groups are as variable through time as small ones. Ecological factors showed no effects on the observed level of between group variability. Within group variability was found to be smaller than the level of between group variability in all species tested. The results are related to social organization and to the degree of feeding interference observed within and between troops. Future practical applications for our results are considered.