There are two approaches adressing the relationships between environmental factors and biodiversity, namely, experimental manipulation of number of species within a community and survey of biodiversity along a natural gradient at large scale. In this study, we employed the latter method to investigate the variability of species richness along the altitude gradient in the Xiangxi River Watershed. Xiangxi River originates in the southern slope of Mt. Shennongjia of western Hubei, and runs for 94km into the Y...