Global tests of regional effect on species richness of vascular plants and terrestrial vertebrates

Determining the effects of regional and contemporary factors on large-scale patterns in species richness has been a fundamental question in modern ecology and biogeography. However, few studies have examined effects of historical and regional factors on species richness at the global scale, and conclusions are often inconsistent or controversial. Here, I use a comprehensive dataset to examine regional effects on species richness of vascular plants and four taxa of terrestrial vertebrates (mammals, birds, reptiles, and amphibians) in the same set of sample units (ecoregions) in seven biogeographic realms across the globe. The same spatial scale and the same set of environmental variables, which are thought to influence large-scale patterns in species richness of vascular plants and terrestrial vertebrates, are used for all the five taxa. Species richness of each taxon is compared across biogeographic realms. Regional effect on species richness has been found for all the five taxa. Of the 90 realm-pair comparisons for the five taxa between observed richness of a region and the richness of the region predicted by the richness–environment relationship derived from the data of another region, 74 (82.2%) showed significant differences between observed and predicted species richness, indicating that a species richness–environment relationship developed for one region cannot accurately predict species richness in other regions of similar environments.