The reproduction of any species can be best understood by placing it within its ecological context. This research project is designed to test the hypothesis that reproduction, specifically female ovarian function, is effected by environmental conditions. The study will investigate whether food intake and activity levels affect ovarian hormonal levels (and hence the biological capacity to bear offspring). Orangutans are and ideal species to examine the effects of energy expenditure on fecundity for a variety of reasons. 1) Orangs have the longest average inter birth interval of any primate - 8 years, with a great deal of variability surrounding it; 2) this implies a long period after lactation, called the waiting time to conception, in which females are not yet fecund for a variety of reasons including local ecological conditions and maternal condition; 3) the slow movement of orangutans facilitates collection of detailed data on nutritional intake and energetic expenditure; 4) they inhabit an area of large fluctuations in fruit availability, so that if ovarian function responds to fluctuating fruiting patterns, this is a habitat where such a relationship is likely to be expressed. The research in West Kalimantan, Indonesia will focus on females who have finished lactating for one offspring and have not yet conceived again. The data will consist of relative hormonal indices reflecting ovarian function during each cycle that will be compared to data gathered simultaneously on estimates of nutritional intake, energetic expenditure, energy balance and food availability, testing the responsiveness of ovarian function to these variables. To accomplish this, techniques of measuring urinary hormones will be used to evaluate ovarian function. Additionally, monitoring cyclical fluctuations in hormonal patterns will make it possible to address whether aspects of orangutan socio-sexual behavior, such as the surprisingly regular occurrence of forced copulations, are influenced by ovulatory status. Knowing when ovulation occurs will provide a powerful tool to investigate the role of female choice and its impact on sexual selection in orangs.
