Noninvasive genetic assessment of the population trend and sex ratio of the Shennongjia population of Sichuan snub-nosed monkeys (Rhinopithecus roxellana)

Effective population management relies on assessments of population size and sex ratio. However, these estimates are difficult to obtain for elusive and rare species. Recently, noninvasive genetic census methods have been developed as an alternative to traditional capture-mark-recapture methods. In this study, we estimated the size of the Sichuan snub-nosed monkey (Rhinopithecus roxellana) population in the Shennongjia Nature Reserve (SNR) using a noninvasive sampling method based on 16 microsatellite loci. We also used a PCR-based genetic method to sex the sampled individuals and infer the population sex ratio. The population size of R. roxellana in the SNR was estimated to be 1044 individuals (95% CITIRM: 613-1409). The estimated population sex ratio is more female-biased than expected, which we attribute to the sampling biased towards one male units and limited sampling of bachelor male units. Moreover, there is no suggestion that the heavy traffic road through the reserve might block movement of monkeys. The results of this study indicate genetic assessments based on a noninvasive sampling method can provide useful information regarding populations of elusive primates.