Natal dispersal and new group formation in capybaras (Hydrochoerus hydrochaeris) in a seasonally flooded savanna of Venezuela

by Congdon, Elizabeth Rae

This study examines natal dispersal and new group formation in capybaras (Hydrochoerus hydrochaeris) in a seasonally flooded savanna in Venezuela. The first section describes a novel approach to the study of dispersal that could be applied to many taxa. Dispersal is considered in three stages (emigration, transience, and immigration) and its proximate and ultimate mechanisms are clearly differentiated. The second chapter describes dispersal behavior in capybaras, including which individuals disperse, when, and to where. In the third chapter, I evaluate dispersal in capybaras with respect to social subordination and social cohesion hypotheses. In this population, some support was found for the social subordination hypothesis, although results were not always straightforward. Little evidence was found for the social cohesion hypothesis. All dispersers were male and very few males were philopatric. Taken together, these data suggest that young dispersing males are more aggressive (both initiating and receiving more aggression) and less tolerated by adult males than are females of similar age. This population appears to have two behavioral classes of individuals that follow gender roles: aggressive-dispersive males; and tolerant-philopatric females. The aggression initiated by young males is suggestive of a social variation of the ontogenetic switch hypothesis wherein maturing males switch from being submissive juveniles to aggressive subadults. While most social hypotheses for dispersal focus on the reactions of juveniles to adults, this study suggests a primary role of the behavioral maturation of the disperser. In the final chapter, the ultimate drivers of dispersal are considered in light of the behavioral data collected. The tendency for aggressive interactions to be intra-sexual Congdon, Elizabeth, UMSL, 2007 p. 3 suggests mate competition is an important driver of dispersal in this species. Although genetic data are not yet available, the high costs of dispersal and differences between natal and breeding groups further support the mate competition hypothesis for the evolution of dispersal in capybaras. Understanding dispersal in this highly social species provides valuable insight concerning the relationship between habitat and social structure. In the context of extensive, and often rapid, anthropogenic environmental changes, the ability to predict a species response to change becomes increasingly important. Congdon, Elizabeth, UMSL, 2007 p. 4