An assessment of potential distribution and climate change impacts on a critically endangered primate, the Delacour's langur

The Delacour's langur (Trachypithecus delacouri) is a critically endangered and endemic primate that inhabits a small region in North Vietnam. While the main threats to the langurs include illegal hunting and habitat destruction, the potential impacts of climate change on this species have never been assessed. In this study, we used Maxent, a species distribution modelling approach that has been shown to be suited for rare species, to assess the effects of climate change on the distribution of the Delacour's langur in different future scenarios. We constructed an optimally tuned model to predict climatically suitable habitat for T. delacouri in current conditions, then projected the models to three future periods, 2041-2060, 2061-2080, and 2081-2100 using data from three general circulation models. Our models showed high predictive performance and successfully predicted the current known range, but also showed areas of overprediction that may reflect a part of the langur's ecology. Our results estimated an overall loss in total suitable habitat, with an average value of approximately -26.97% in the 2041-2060 period, -29.81% in the 2061-2080 period, and -15.48% in the 2081-2100 period, compared to the current predicted range, but they also predicted the currently important Van Long-Kim Bang region as suitable across all future scenarios. We suggest that some of the predicted climatically suitable areas, including Van Long, Kim Bang, Lac Thuy, and Cuc Phuong, may be crucial for future conservation and population re-establishment/re-introduction activities of the Delacour's langur.