Effects of Climate Change and Forest Fragmentation on the Ecology and Genetic Diversity of White-Thighed Colobus, Colobus Vellerosus, West Africa

Abstract

The white-thighed colobus (Colobus vellerosus), a Critically Endangered primate endemic to West Africa, faces imminent extinction due to rapid habitat loss, intense anthropogenic pressures, and accelerating climate change. For several years, it has been listed among the IUCN’s top 25 most endangered primates, underscoring the need for urgent and effective conservation actions. This dissertation presents the first comprehensive, multi-scalar assessment of the species' climatic niche, land-use dynamics within its distribution range, habitat connectivity, and genetic status. By integrating species distribution modelling, long-term landscape analysis, connectivity modelling, and population genetics, this work establishes a robust, spatially explicit foundation for needed conservation interventions. First, using ensemble species distribution models (SDMs) that disentangle climatic from anthropogenic effects, I show that precipitation during the driest month, annual mean temperature, and forest cover are the primary drivers shaping the distribution of C. vellerosus. Current anthropogenic pressures have already led to the loss of 36% of climatically suitable habitats, and even under an optimistic climate scenario, suitability is projected to decline by approximately 73% by 2050. Second, a 36-year land-cover analysis (1989-2025, corresponding to four generations of C. vellerosus) reveals pervasive landscape transformation across the species’ central Benin range. Forest cover has declined by 50% and savannah by 35%, while cropland expanded by 128%. Transition intensity analysis shows that conversions from forest to cropland and forest to settlement are dominant. This aligns with local perceptions, as 60% of surveyed residents acknowledged forest decline, though the accuracy of these perceptions varied only slightly with socioeconomic factors. These findings emphasise that anthropogenic land-use change is both extensive and community-recognised, yet insufficiently integrated into current management strategies. Third, a regional comparison of C. vellerosus and its parapatric congener C. polykomos demonstrates major mismatches between climatically suitable areas and current distributions, with both species exhibiting severe future range contractions. Although substantial areas of climatically suitable forest persist, 48–83% of these regions fall outside protected areas, underscoring potential opportunities for strategic habitat protection and planning for reintroduction. Fourth, through the modelling of functional connectivity via resistance surfaces in central Benin, least-cost paths, circuit theory, and graph-theoretic metrics, I demonstrate that fragmentation has resulted in a dual landscape: highly permeable corridors in the south (linking Monts-Kouffé, Kikélé, and Wari-Maro) contrasted with isolation in the north. The Monts-Kouffé–Wari-Maro complex emerges as the primary connectivity nucleus, with several medium-sized patches functioning as vital stepping stones, whose loss woulddisproportionately impair network integrity. Furthermore, mitochondrial DNA analysis of the two observable populations in central Benin (KSF and OKF) reveals extremely low genetic diversity, characterised by only one cytb haplotype and two nearly identical D-loop haplotypes, indicative of a severe founder effect and prolonged isolation. This significantly low mitochondrial variation highlights the urgent need for a comprehensive species-wide genetic assessment and the exploration of translocation-based genetic rescue strategies. Across all analyses, this dissertation illustrates that C. vellerosus faces significant threats from the simultaneous impacts of climate-driven niche contraction, long-term land-use transformation, severe habitat fragmentation, and dramatically reduced genetic diversity. Conservation priorities identified include: (1) protecting and restoring climatically resilient forest refugia, (2) enhancing community-managed and unprotected forests within connectivity networks, (3) establishing ecological corridors informed by functional connectivity outputs, (4) developing reintroduction and genetic rescue programs aligned with IUCN standards, and (5) integrating long-term ecological monitoring with community engagement and adaptive governance. Collectively, this work provides the first comprehensive conservation framework for C. vellerosus, from landscape to genome, offering actionable guidelines to prevent the extinction of one of West Africa’s most imperilled primates.