Student Prize Award Abstract
1995 Poster Paper Award

INTRAGROUP SPACING AND AGONISTIC INTERACTIONS IN WHITE-FACED SAKIS

T.M. Gleason and M.A. Norconk
Department of Anthropology, Kent State University, Kent OH 44242

Spacing of individuals in social groups is best regarded as a compromise between maintaining (a) close proximity to other group members for the sake of collective vigilance and (b) dispersion to minimize intragroup competition for food. The outcome of dominance interactions is also likely to affect group geometry. We report the results of a four month study of white-faced sakis, Pithecia pithecia (5 males and 4 females) on a 15 hectare island in Lago Guri, Bolivar State, Venezuela. A 3-dimensional measure of group spacing and a measure of individual centrality were used to test hypotheses regarding the ecological and behavioral correlates of intragroup spacing. The dominant female occupied the front-center of the group in more than 75% of all samples, while the position of the dominant male, and other group members varied considerably. We found no significant association between group spread and access to food items. Mean nearest neighbor distances were lowest among females and highest between males and females. This trend was most pronounced during agonistic interactions. We witnessed four males form temporary coalitions against the fifth and repeatedly drive him from the group. Twenty-nine such episodes with an average duration of 26 minutes occurred during a 45 day period. Females were nearly three times as likely to be within 2 meters of another female both during and after these episodes. Our results suggest a strong relationship between dominance interactions and group geometry. Supported by an REU supplement to NSF grant DBS-90-20614.