The geography of connectivity shapes plant endemism hotspots

Abstract

The high biodiversity in mountains is attributed to species accumulation from dispersal, high habitat heterogeneity and local speciation. Landscape connectivity thereby influences colonization and speciation processes, making its net effect on biodiversity challenging to understand. This is especially true for complex and biologically diverse mountain systems, such as the Hengduan Mountains (HDM), with their remarkably high levels of endemism. Here, we mapped the distributions of 3165 endemic plant species (25% of the region's total richness) in the HDM and studied the complex interplay between landscape connectivity and climate as drivers of endemic richness, as well as endemic compositional turnover. We found that endemic richness peaks at elevations of 3000 to 4000 m a.s.l., about 1000 m higher than that of overall richness. Mean temperature of the warmest quarter, climate change velocity since the Last Glacial Maximum, and connectivity together explain patterns of both α- and β-diversity of endemism. Our models show strong explanatory power along the elevation gradient and across the landscape. Our findings point to a distinct, context-dependent role of landscape connectivity in shaping biodiversity. In the endemic hotspot of the central-western HDM, particularly within the Three-Parallel-Rivers Region, endemic diversity indices are negatively associated with landscape connectivity. In contrast, we found a positive association between endemic richness and connectivity in the northern and southern HDM, which have overall lower endemism levels. This context-dependent effect of the connectivity–richness relationship highlights the complex influences of geomorphological processes on endemic patterns at a regional spatial scale.