Negotiating social space in vervet monkeys

Abstract

This study explores the effect of changing ecological conditions on female social organization among free-ranging vervet monkeys (Cholorocebus aethiops pygerythrus) in the Klein Karoo, South Africa. Comparison was made between a previous study conducted during a period of drought in 2009, and my own study conducted when conditions were much wetter and hence, less ecologically stressful. In addition, animals in the present study also experienced conditions of low demographic stress. Compared to 2009, females displayed lower rates of competition and aggression, did not compete for access to grooming partners, and did not preferentially groom those of high rank, nor did they do so more frequently. Females did, however, preferentially associate spatially with those they groomed most; a finding in contrast to the previous study. Females did not groom those of adjacent ranks more frequently, nor was there any relationship between rank difference and spatial association. In addition, there were rank differences in vigilance were found between females, and vigilance costs overall were affected by total group size. Overall, these findings support some aspects of the socioecological model used to predict group structure in primates, but other aspects of social organization remain puzzling, and may reflect larger overall group sizes in the Samara population, which changes patterns of engagement between females in ways not fully captured by current models.