ASIAN COLOBINE SOCIAL-STRUCTURE - ECOLOGICAL AND EVOLUTIONARY CONSTRAINTS

Both ecological and phylogenetic factors and their interaction influen ce primate social structure. Food resources, in particular, affect soc ial structure parameters such as sex/age composition, group size, home range size, and individual density. As a group, the Asian colobines m ay be partially buffered from the impact of food constraints on social structure, given their specialized digestive physiology. Asian colobi nes are able to subsist on mature foliage, a relatively abundant and n on-patchily distributed resource, when preferred foods are not availab le. In food limited populations, increases in group size or density sh ould cause increases in home range size. We did not find this relation ship for Asian colobines, however, and thus it would appear that the m ajority of Asian colobine populations are below carrying capacity. Foo d may be less of a limitation to populations than other factors, such as social stress. The formation of bands (associations between relativ ely stable groups) has been documented for both Nasalis and Rhinopithe cus, and based on recent data for several Presbytis and Trachypithecus species, we predict that band formation is the norm for the Asian col obines, including Pygathrix. Group home ranges for Plesbytis and Trach ypithecus species typically overlap and both intergroup tolerance and intergroup aggression are observed. This suggests that groups form dif ferentiated relationships, tolerating some groups but not others. Such differentiated relationships are the foundation of band formation.