Understanding the determinants of primate biomass is an important aspect of deciphering behavioral adaptation and of guiding conservation planning. Because most of the variation exhibited in primate communities can be accounted for by leaf-eating species, previous research primarily focussed on folivorous primates. The major factors suggested to influence folivore biomass are leaf quality, seasonality, habitat heterogeneity, and resource competition. However, most research has focussed on primates of the Old World. Because New World monkeys exhibit a different digestive morphology, the results may not be representative. More importantly, most of the previous research has investigated possibly influencing factors individually (univariate). However, recent research in paleobiology and ecology has revealed a more complete understanding of complex processes through multivariate approaches. This study will take such a multivariate approach investigating the factors influencing the biomass of the most folivorous neotropical primate, the red howler monkey (Alouatta seniculus). Guided by previous research results, we identified 10 ecological variables with unique predictive combinations for 15 demographic and behavioral variables. The unique signatures for each individual variable allow identifying the most important factors, which are driving population densities. The project will be the first of its kind to use such a wide-ranging approach. It will also provide a comparative basis to determine whether factors influencing biomass are similar across taxa from different primate radiations. The study will take place at Yasuni National Park, Ecuador, an area of extreme biodiversity and one of UNESCO's "Man and the Biosphere Reserves". Data will be collected at two sites in close proximity (ca. 40 km apart) differing in population density of red howler monkeys, general habitat characteristics, and hunting pressure. Data collection will include monitoring the demography and densities of the two primate communities, observation of the activity and ranging behavior of altogether 7 groups, and collection of fecal samples and visual assessment of bot fly infestations to judge parasite load. The ecology of the habitat will be monitored based on botanical and phenological transects. Soil and food samples will be taken and their nutrient content analyzed. Finally, interviews with local Huaorani hunters and market surveys will serve to monitor hunting pressure. In terms of broader impact, the aims are 3-fold. The study will provide key data to be incorporated into future management plans of the park. In addition, the study provides training and career opportunities for assistants from Ecuador and other countries and is build upon and encourages cooperation with institutions in Ecuador (Universidad San Franscico de Quito, Ponticifica Universidad Catolica de Ecuador), USA (Cornell University), and Germany (University of Hamburg). Lastly, the project encourages an active involvement of the local community in the park and the project. During the preparatory parts of the study monthly meetings with three Huaorani Indian communities have been established in order to aid in conservation efforts, provide them with information about the ecology of their forest, and how the results of this study may impact their lives.
