Testing the correlation between beta diversity and differences in productivity among global ecoregions, biomes, and biogeographical realms

a r t i c l e i n f o Keywords: Beta diversity MODIS NDVI Mantel test Multivariate distance WWF ecoregion Biogeographical Evolutionary history Considerable amount of research on the relationships between species diversity and productivity at different spatial, ecological, and taxonomic scales has been conducted. However, the overall trend of the correlation at the global scale still remains sketchy and the causal relationship between species diversity and productivity needs further exploration. This is especially true with beta diversity since most studies carried out use alpha diversity as the general term for species diversity. In this study we use the MODIS NDVI as the surrogate of productivity, and the WWF ecoregion systems and its species distribution information to test correlations between beta diversity and differences in productivity at various taxonomic ranks on a global scale. Matrix correlation is performed between species composition measured as beta diversities using Sørensen similarity index and MODIS NDVI/productivity measured as Bhattacharyya distances through Mantel permutation tests. The correlation coefficients and Mantel test significance levels are reported at the global ecoregion, biogeographical realm, and biome levels respectively. Significant correlations are found at all three taxonomic ranks. Results from realm and biome tests suggest that the highest correlations are reached at the temperate regions when species rank is used. Our findings suggest that species' natural spatial boundaries, such as the biogeographical realms or biogeographic kinship play a critical role in shaping the correlation patterns between beta diversity and productivity differences at the global scale. The relationship between species diversity including alpha (richness) and beta (taxa turnover) and the productivity is important to both ecological and biogeographical theories and biological conservation practices. Considerable studies on the relationships at different spatial, ecological and taxonomic scales have been conducted during the past decades. On alpha diversity, two general patterns have emerged: (1) at the local scale, competitive exclusion theory predicts a unimodal relationship between productivity and diversity (2) at a regional or global scale, species-energy theory reports that diversity-productivity relationships are often monotonically increasing (Wright are also postulated to explain the patterns and seek casual relationships between species diversity and productivity. We observed that most of the studies are limited either to a particular taxon groups or to a particular region; and diversity is measured as species richness only. The overall pattern of the correlation between species diversity, especially the beta diversity and the changes in productivity at the …