Spatial scale and cross-taxon congruence of terrestrial vertebrate and vascular plant species richness in China.

In ecology and biogeography it is often recognized that the species richness of different groups of organisms is spatially congruent (and thus positively correlated). However, ecological phenomena are often scale dependent and can change with spatial scale (i.e., grain size and extent). Because species richness gradients are also correlated with environmental gradients and plant species richness is thought to influence animal species richness, the relative roles of environment and plant richness in influencing cross-taxon congruence of animal richness at different spatial scales remain poorly explored. In this study, we examine the spatial concordance in species richness among terrestrial vertebrates and vascular plants at two spatial grain sizes (local and regional) across China. We hypothesize that (H1) cross-taxon richness relationships are weaker at the local scale; (H2) climatic predictors of species richness are stronger at the regional scale; (H3) effects of habitat heterogeneity on species richness are stronger at the local scale; (H4) plant richness positively affects vertebrate richness after accounting for environmental effects; and (H5) the plant-vertebrate richness relationship is weaker at the regional scale. We found significant and positive correlations between species richness of the groups, with correlations being stronger at the regional scale than at the local scale (supporting H1). Climate has weaker effects on species richness at the regional scale than at the local scale (rejecting H2), and for vertebrates (but not for plants) effects of habitat heterogeneity are stronger at the local scale (supporting hypothesis H3). Plant richness positively affects vertebrate richness after accounting for environmental effects (supporting H4), but the effect is stronger for the two endothermic groups (mammals and birds) than for the two ectothermic groups (reptiles and amphibians). In contrast to hypothesis H5, the effect of plant richness on species richness of vertebrates is stronger at the regional scale than at the local scale. Our study suggests that plant richness has a significant influence on animal species richness across spatial scales and that the strength of the effects of plant species richness, climate, and topographic heterogeneity on animal species richness depends on the spatial grain size of sampling units.