Using water and energy variation to explain the botanical richness pattern of Theaceae species in southern China

Abstract Background Energy and water availability are essential for biodiversity maintenance. In addition to the independent effects of water and energy on biodiversity, recent studies clarified that the effects of interaction between water and energy availability were indispensable. Methods In this exercise, by combining the species presence information and the environmental predictors, we produced species distribution models at 20 × 20 arc-minute resolution for 193 Theaceae species. Initially, the ordinary least square (OLS) regression was used to examine the stationary relationships between Theaceae diversity and climate. The statistical effects of water and energy on species diversity were detected using Geographically Weighted Regression analysis (GWR). Furthermore, the contour plots were used to view the statistical effects of the water and energy interaction on species diversity. Results The OLS results suggested that both energy and water availability are related to Theaceae species diversity. In GWR regression, the spatial variation of energy and water showed high explanatory power to the diversity pattern of Theaceae species. The patterns in the residuals of both OLS and GWR regression varied geographically. Therefore, the results of GWR regression were kept for further analysis. The value of diversity-water slopes decrease changed from positive to negative in extremely wet regions; In extremely dry conditions, the value of diversity-energy slopes decrease faster than other regions. Conclusions Our results support the following findings: 1) the latitudinal distribution of Theaceae species was limited by thermal tolerance, which support the freezing-tolerance hypothesis in macro-ecology; 2) Theaceae species diversity are sensitive to the instability of precipitation, while the limitation from energy availability is weak; 3) the effects of water and energy on species diversity are strong in dry regions. Those findings can provide further implications for Theaceae species conservation under climate change scenarios.