Many primate populations currently live in forest fragments. These populations are often unhabituated, elusive, and contain few individuals, making them difficult to study through direct observation. Noninvasive genetic methods are useful for surveying these unhabituated populations to infer the number and sex of individuals and the genetic diversity of the population. We conducted genetic analysis on 70 fecal samples from eastern chimpanzees (Pan troglodytes schweinfurthii) in Gishwati Forest Reserve, a forest fragment in western Rwanda. We genotyped all but two of these samples using 12 autosomal and 13 Y-chromosome microsatellite markers previously used in analyses of other chimpanzee populations. The genetic data show that these samples represent a minimum of 19 individuals (7 females, 12 males). However, because we may not have sampled all individuals in the population, we also performed mark-recapture analysis with the genetic data and found that the entire population likely numbers between 19 and 29 individuals. These results are consistent with opportunistic observations of at least 19 individual chimpanzees. Levels of variation at the Y-chromosome microsatellites were similar to those observed in other chimpanzee communities, suggesting that the chimpanzees in this forest are members of a single community. These results provide a baseline count of the number of male and female chimpanzees in the Gishwati Forest Reserve, and the data provide the potential for follow-up studies aimed at tracking individuals over time, thus aiding conservation management of this unhabituated population.
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The Great Ape Trust provided funding for this study. We thank the Government of Rwanda for their support of our research in Gishwati Forest Reserve. We also thank Benjamin Beck, Madeleine Nyiratuza, Sylvain Nyandwi, Peter Clay, Thomas Safari, Samuel Uwimana, Patience Mwiseneza, Alex Ndayambaje, Isaac Ngayincyuro, Olivier Ngabonziza, and Eric Munyeshuli for both logistical support and assistance in the field. We especially thank Hjalmar Kühl for assisting with the map. We thank Christophe Boesch and Mimi Arandjelovic for discussion, Roger Mundy for assistance with the accumulation curve estimation, and Carolyn Rowney for assistance with laboratory work. In addition, we thank two anonymous reviewers and Joanna Setchell for comments on previous versions of the manuscript. The Max Planck Society provided funding for laboratory work.
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Chancellor, R.L., Langergraber, K., Ramirez, S. et al. Genetic Sampling of Unhabituated Chimpanzees (Pan troglodytes schweinfurthii) in Gishwati Forest Reserve, an Isolated Forest Fragment in Western Rwanda. Int J Primatol 33, 479–488 (2012). https://doi.org/10.1007/s10764-012-9591-6
- Mark recapture
- Noninvasive sampling
- Pan troglodytes schweinfurthii