Climate, human disturbance and geometric constraints drive the elevational richness pattern of birds in a biodiversity hotspot in southwest China

To improve our understanding of mechanisms underlying biodiversity patterns, and provide insights for conservation biologists, elevational pattern of bird species richness and its causes were studied in the Gaoligong Mountains, China. On the east slope of the southern part of Gaoligong Mountains (24.79°N-26.49°N, 98.65°E−98.93°E), we conducted field surveys of birds at each 300-m band from 700 to 3400  m a.s.l., and for the two bands from 3400 to 4000  m a.s.l., we obtained data from historical records. We obtained climatic recording data from local meteorological stations that were located in our study area and calculated the mean annual temperature and precipitation. We also calculated the Area, MDE (the mid-domain effect), NDVI (the normalized difference vegetation index), habitat heterogeneity and human disturbance for each 300-m band. We then used multiple regression analysis to test the explanatory power of different factors for the elevational richness patterns of overall, endemic, non-endemic, large-ranged, and small-ranged birds. A total of 277 breeding bird species were recorded. We found consistent hump-shaped elevational patterns of species richness with varied peaks for different groups. The richness of endemic birds peaked at higher elevation than non-endemic birds. Although none of the seven factors (Area, MDE, mean annual temperature, annual precipitation, NDVI, habitat heterogeneity, and human disturbance) showed consistent explanatory power among different species groups, temperature and human disturbance played important roles in shaping the richness patterns of most bird groups whereas MDE contributed to the richness pattern of large-ranged species. Our results highlight the need to increase conservation effort at the low elevation of this biodiversity hotspot where there is high richness of birds but intensive human land use. Furthermore, more studies are needed in this biodiversity hotspot to clarify the detailed influence of climate change on elevational distributions of birds.