a decreasing trendP >0.05
Along latitudinal gradients, total species richness ( S ) generally exhibited a decreasing trend of a logarithmic function ( R 2 = 0.185, P >0.05), but it presented a significant variation of a quadratic function with a trend of initially increasing and then decreasing at latitudinal belts from 37.5° to 40° ( R 2 = 0.885, P <0.01).