? Springer-Verlag 1993 Constraints on group size in primates and carnivores: population density and day-range as assays of exploitation competition

Summary. We hypothesise that foraging group size (FGS) and population group size (PGS) in primates and carnivores are related to quantifiable variables indexing the intensity of exploitative competition. Group size is predicted to increase with both food density and travel capabilities, as estimated by the "constraint-free day-range " (DRy), i.e. the day-range of a solitary individual uninfluenced by competition from conspecifics. We test this "exploitation competition " hypothesis among pri-mates and carnivores, using data on populations, species and genera. Food density was indexed by population density. Where DRs could be estimated by regression it was found to be correlated with observed day-range (DRm). DRs was therefore indexed by DRm in all species. Population density and DRm were associated with each other, but in a multiple regression each variable contrib-uted independently to explaining variation in group size. PGS was predicted better than FGS, but regressions in-volving either measure of group size were significant in all analyses. The multiple regression analyses were vali-dated by the method of linear contrasts, which accounts for possible lack of independence among taxa. We con-clude that species differences in group size are influenced by both food density and DRs. This suggests that varia-tion in the intensity of exploitation competition is partly responsible for differences in group size