Niche Expansion and Terrestriality in an Arboreal Primate

University Of Wisconsin-Madison, Madison WI

Investigators

Abstract

Most comparative models of primate behavioral ecology assume that the behaviors of wild primates are adaptive, or are the products of selection pressures under ecological conditions in the past. Yet, the fast pace at which human activities alter the environment results in new ecological challenges and makes it difficult to distinguish evolutionary adaptations from more rapidly acquired behavioral responses that may or may not be adaptive over time. Understanding this plasticity is fundamental to analyses of evolutionary mechanisms and represents an urgent priority for assessments of the future of endangered primates living in disturbed habitats. This study builds on a unique historical database from the long-term field study of wild northern muriqui monkeys (Brachyteles hypoxanthus) in the Atlantic Forest of southeastern Brazil to evaluate how ecological change drives behavioral innovations and to identify the social pathways by which new behavior patterns spread within and between groups. The northern muriqui is critically endangered, and with 281 individuals confined to a 957-hectare protected forest fragment, the study population represents more than 25% of the entire species. During the past 27 years, the population has quintupled in size and the population's density is now the highest known for the species. Previous behavioral adjustments to population pressures have included shifts from cohesive to fluid grouping patterns. More recently, and despite their arboreal lifestyle, the largest group in the population has undergone a 20-fold increase in its use of the ground and all three of the other smaller groups now engage in terrestrial feeding. The greater risks from terrestrial predators and pathogens imply that this change in the muriquis' habitat use is an extreme manifestation of an overall expansion of their ecological niche necessitated by the population's growth within a confined area. With the collection of systematic behavioral data on all four muriqui groups in this crowded population, this study will quantify the ecological implications of niche expansion and the social processes by which newly acquired behavior patterns are diffused between groups by dispersing females and subsequently spread within groups along established social networks. The intellectual merits of the study include the new comparative perspectives it will provide into the ecological conditions associated with ground use in other primates, and the critical insights it will provide into the adaptive potentials of contemporary primates and their prospects for survival in a rapidly changing world. In addition to its scientific contributions, this study will provide essential continuity for the only long-term study on this critically endangered species and one of the longest-running field studies of any primate. It will contribute to the conservation and protection of one of the last remaining strongholds for northern muriquis, and maintain the researcher's longstanding tradition of providing training opportunities for Brazilian students. The established record of collaborative research and conservation activities, and success with capacity building in Brazil, extend the broader impacts of this study to include an international conservation and educational agenda.