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. / xi, 122 leaves ; 29 cm

Narrow riparian woodlands along non-perennial streams have made it possible for vervet monkeys to penetrate the semi-arid karoo ecosystem of South Africa, while artificial water points have more recently allowed these populations to colonize much more marginal habitat away from natural water sources. In order to determine the sequelae of life in these narrow, linear woodlands for historically 'natural' populations, I determined the size of troops in relation to their reliance on natural and artificial water sources and collected detailed data from two river-centred troops on activity, diet and ranging behaviour over an annual cycle. These data indicate that river-centred troops were distinctive primarily for their large group sizes and, consequently, their large adult cohorts, and the extent of home range overlap in what is regarded as a territorial species. While large group size carried the corollary of increased day journey length and longer estimated interbirth intervals, there was little other indication of ecological stress. Specifically, the rate of predation appears to be lower than observed at other sites. Predation encounters here, encourage the use of predator vigilance rather than influencing the use of space within the habitat. The high density of Acacia karoo, which accounted for a third of annual foraging effort in what was a relatively depauperate floristic habitat, allows for an adequate energy intake for groups of this size. I ascribed the large group size and home range overlap to the inability of groups to undergo fission. / xiii, 79 leaves : ill., maps ; 29 cm