Monsoon Climate and Anthropogenic Influences Shape Primate Distributions across the Southeastern Edge of the Qinghai-Tibet Plateau

Abstract The southeastern edge of the Qinghai-Tibet Plateau (Yunnan, China) exhibits high biodiversity but stark differences in species richness between its western Longitudinal Range Gorge (LRG) and eastern Yunnan Plateau (YP). We collected distribution data for 16 primate species in Yunnan and analyzed palynological records over the past 20 ka from 21 localities to identify the biogeographic, climatic, and anthropogenic factors that have driven the present-day distribution of primates in this region. By integrating local ecological records, field surveys, species distribution models, niche utilization rates, and historical vegetation and land use changes, we found that spatial-temporal shifts in monsoonal climate have been a critical factor in shaping primate species richness on the southeastern edge of the Qinghai-Tibet Plateau. Compared to the YP, the LRG receives more precipitation, has more limited seasonal temperature variation, and has higher minimum temperature of coldest month. These conditions have facilitated the development of moist evergreen deciduous forests, which represent a more suitable habitat for the 14 primate species that inhabit this area. In contrast, the drought-adapted forests of the YP support only one primate species. Palynological records indicate that the differentiation of the LRG and YP predates human influence. However, over the past 2,000 years, anthropogenic habitat loss and hunting have significantly affected the distribution of primates. The ranges of gibbons, langurs, and snub-nosed monkeys are now restricted to the central and northern regions of the LRG and have disappeared from lower elevations. Lorises have disappeared from their northernmost range. In contrast, the distribution of macaques has remained relatively stable. The Yangtze-Red River-24°N line marks the biogeographic boundary of high primate species richness and biodiversity in the LRG and southeastern Yunnan. Our research suggests that changes in monsoon climate have fundamentally shaped contemporary species richness, while recent anthropogenic pressures have caused 'range contraction' for many taxa.