Food abundance affects energy intake and reproduction in frugivorous female Assamese macaques
In most mammals, female fertility and reproduction are strongly influenced by nutritional status and, therefore, by foraging conditions. Here, we investigate the relationship between food resources, feeding competition, energy intake and reproduction in a group of wild female Assamese macaques (Macaca assamensis) in northeastern Thailand. Over 2,100 h of data on feeding behaviour, energy intake and activity budgets were combined with data on resource characteristics, female reproduction and physical condition. We found that an increase in food availability had a positive effect on female energy intake and conception rates. In addition, it appeared that females incurred energetic costs during lactation and that females with a better physical condition during the mating season were more likely to conceive. The annual birth season occurred a few months before the annual peak in food availability, causing peak lactation to coincide with a period of high food availability. This suggests that females use the increased food abundance to compensate for the energetic costs of lactation. Neither energy intake rates nor activity budgets were influenced by female dominance rank, even during periods when the levels of contest competition were predicted to be high. In line with this, we found no evidence for rank-related differences in reproduction. The apparently limited influence of feeding competition in female Assamese macaques adds to the debate on the extent to which patterns in feeding competition and fitness can reliably be predicted based on ecological conditions. We suggest that this may partially be resolved by including potential competition-reducing mechanisms into the predictive framework.
KeywordsAssamese macaque Feeding competition Reproduction Energy budget Seasonality Nutrition Ecology
We thank the National Research Council of Thailand (NRCT) and the Department of National Parks, Wildlife and Plant Conservation (DNP) for permission (no. 0004.3/3618; 0002.3/2647) to conduct this study. We are grateful to J. Prabnasuk, K. Nitaya, M. Kumsuk and K. Kreetiyutanont (Phu Khieo Wildlife Sanctuary) for their cooperation and permission to carry out this research. We thank A. Koenig and C. Borries (Stony Brook University) who developed the field site at Huai Mai Sot Yai. We are very thankful to N. Juntuch, N. Ponganan, D. Bootros, S. Jomhlotwong, T. Kilawit, T. Wisate, P. Saisawatdikul and especially M. Swagemakers for their help in the field. We are also very grateful to W. Nuagchiyo, A. Chunchaen and S. Macdonald for their help with data collection. We thank N. Bhumpakphan, W. Eiadthong (Kasetsart University) and W. Brockelman (Mahidol University) for their support and cooperation. Furthermore, we would like to thank Dr. Marie Charpentier and two anonymous reviewers for helpful comments on an earlier draft of the manuscript. This project was supported with funds from the Max Planck Society, the National Geographic Society and the University of Göttingen through funding from the German Initiative of Excellence.
Conflict of interest
The authors declare that they have no conflict of interest.
Approval and permission to conduct research was granted by the authorities of Thailand (permit no. 0004.3/3618 and 0002.3/2647), and all research was undertaken in strict accordance with the laws set forth by the National Research Council of Thailand and the regulations of the Department of National Parks, Wildlife and Plant Conservation, Bangkok, as well as the guidelines of the involved institutes.
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