Mammal and butterfly species richness in Chile: taxonomic covariation and history
Understanding species richness spatial distribution is of fundamental importance to face the current biodiversity crisis that affects biotas around the world. Taxonomical covariation in species occurrence may offer the possibility to identify common factors that restrict species richness, as well as some guidelines to the identification of key areas for conservation purposes. To this aim, we analyze the geographic distribution of mammals and butterflies in Chile using 0.5° latitude and longitude quadrats. We found that, for both taxa, there is a strong bell-shaped latitudinal gradient in species richness with a peak at mid-latitudes (33-43° S). The results from multiple stepwise regression analysis shows that for both taxa productivity measured using the Normalized Difference Vegetation Index (NDVI) is the most important variable driving changes in species richness followed by glaciation and elevation depending on the taxa. Mid-domain effects were either weak or unimportant in affecting the richness pattern. Variance partitioning analysis shows that the spatial components alone are irrelevant to the richness pattern. We show that spatial covariation in richness of butterflies and mammals, is strongly influenced by spatial scale, possibly as the result of a scale-dependent effects on individual species ranges, whereas factors related to specific ecological characteristics, are more important at smaller scales. Because richness gradients are ultimately the product of speciation and colonization processes on longer time scales, we propose that species richness gradients in Chile may be explained by the interaction between historical processes associated to desertification and glaciation together with productivity. The former sets the domain within which productivity produces a similar richness pattern for both taxa despite their different phylogenetic histories and physiological requirements.