Identifying suitable forested areas and protected forests for the conservation of white-thighed (Colobus vellerosus) and king (C. polykomos) colobus monkeys under climate change in West Africa

Colobus vellerosus and Colobus polykomos are closely related, parapatric species endemic to West Africa. Both species face severe threats from illegal hunting and habitat destruction, with population declines exceeding 80% for C. vellerosus and 50% for C. polykomos over the past 30 years. Particularly, the critically endangered C. vellerosus necessitates urgent conservation initiatives, including potential reintroductions into suitable habitats where the species has been extirpated in the last decades. We used ensemble modelling to assess habitat suitability for both species under current and future climate conditions, and identified suitable habitats within and outside of protected areas for reintroduction. We found that, under current climate conditions, the size of climatically suitable area for C. vellerosus and C. polykomos is 520,193 km² and 240,398 km², respectively. However, within our area of interest of 1,624,800 km², encompassing 370,000 km² of forest cover, only 7.3% of these forests are suitable for C. vellerosus , compared to 43.3% for C. polykomos . Of these suitable forested areas, 47.9% and 82.9% are located outside protected areas, respectively. Under a low greenhouse gas emission scenario for 2050, these potential habitats may decline by 58.7% and 71.8%, respectively. Key recommendations from our study include protecting suitable habitats, assessing the genetic population structure of C. vellerosus and C. polykomos , developing reintroduction programs for C. vellerosus , and establishing ecological corridors.