Disentangling the relative effects of ambient energy, water availability, and energy–water balance on pteridophyte species richness at a landscape scale in China

Understanding what factors generate geographic variation in species richness is a fundamental goal of ecology and biogeography. Water and energy are considered as the major environmental factors influencing large-scale patterns of species richness, but their roles vary among taxa and regions. Pteridophytes are an ideal group of organisms for examining the relationship between species richness and their environment because the distribution of pteridophytes is usually in equilibrium with contemporary climate to a greater degree than those of seed plants and most terrestrial vertebrates partly due to the lightness of their spores, which is highly capable of long-distance dispersal by wind, and partly due to their single-spore reproduction strategy. Using correlation and regression analyses and structural equation modeling technique, we examine the relationship of pteridophyte species richness in 151 localities from across China with environmental factors representing energy, water, and energy–water balance. We found that pteridophyte species richness is correlated to water availability more strongly than to ambient energy. Furthermore, we found that of all environmental variables considered, energy–water balance has played the most important role in regulating pteridophyte species richness gradients in China.