Primates are unique among mammals in having extended periods of juvenile dependency. Several evolutionary explanations for this prolonged juvenile phase have been proposed, but few of these have been tested in the field, in part because juveniles have rarely been the focus of behavioral research. The few field studies that have explicitly examined juvenile development in primates have focused on taxa that live in female philopatric and female-bonded social groups, neglecting the broad diversity in social organization found in the rest of the Order. By contrast, this study will provide new data on juvenile development and life histories for wild taxa living in societies characterized by a high level of female dispersal, either in cohesive (lowland woolly monkeys, Lagothrix poeppigii) or fission-fusion (white-bellied spider monkeys, Ateles belzebuth) social groups in the Yasuni Biosphere Reserve, Ecuador. In collecting an array of behavioral and developmental data, this study will examine how aspects of juvenile development and behavior may be explicitly tied to social organization, primarily through examining aspects of predation avoidance, food competition and efficiency, and social development that are expected to vary in the different social environments offered by fission-fusion and cohesive groups. This research will also provide the first comparative field test of the most widely accepted explanation for the evolution of extended juvenility in primates, the Ecological Risk Aversion Hypothesis, which argues that the extended juvenile phase in primates is the result of a metabolic slowdown during development arising from the need to remain in the center of social groups to elude predators where high food competition prevents adequate food intake.
Ultimately, this study will fill important gaps in our understanding of the juvenile phase in primates, both through increasing the diversity of juvenile primate data available and by explicitly linking social organization to juvenile behavioral development, which may in turn shed light on the evolution of the markedly extended juvenile phase seen in primates, including humans. Additionally, the scientific presence at the Tiputini Biodiversity Station fostered by the project will enable the training of several field assistants from primate habitat countries, and contribute to the biological station?s mission of Ecuadorian education, ecological discovery, and Amazonian conservation.
