GROUP-SIZE, INFANT DEVELOPMENT AND SOCIAL NETWORKS IN FREE-RANGING RHESUS-MONKEYS

The hypothesis that demographic processes are important in determining social structure among non-human primates through their effects on th e development of individual social relationships was tested. Changes i n maternal behaviour, infants' social milieux and infants' social netw orks were examined as a function of changes in group size and composit ion among free-ranging rhesus monkeys, Macaca mulatta, on Cayo Santiag o, Puerto Rico. Data were analysed for 10 group-years collected betwee n 1974 and 1990 representing a single social group during periods of r apid expansion and fissioning, two daughter groups following fissionin g and an unrelated group that did not undergo fissioning. As group siz e expanded, infants found themselves near (<5 m) larger numbers of gro up members and smaller proportions of close kin. Mothers spent more ti me near their infants and sought more proximity with them. Infants dev eloped social networks that were more highly kin biased. When the grou ps fissioned, these trends reversed. Significant correlations were fou nd between group size, mother-infant interaction and infant social net works across all group-years. Individual variation in the degree to wh ich infant social networks were kin biased was related both directly t o the infant's social milieu and indirectly to its relationship with i ts mother. Given the long-term nature of the mother's influence on soc ial networks, these results suggest that demographic influences on dev elopmental processes can lead to progressive changes in social structu re in the absence of resource scarcity. (C) 1997 The Association for t he Study of Animal Behaviour.