Congruent spatial patterns of ant and tree diversity in Neotropical savannas

The strength of plant-animal diversity relationships tends to be idiosyncratic and, in many cases, its mechanisms are poorly understood. Consequently, the relevance of plant diversity patterns as surrogates of animal diversity patterns is still debated. We evaluated if ants and trees show congruent patterns of species richness and turnover at a regional scale, and the extent to which cross-taxon congruence can be attributed to direct interactions between the two taxa. We surveyed the ant and tree communities in 31 sites scattered over the world's largest tropical savanna (the Cerrado), and found that tree and ant species richness are positively correlated. Furthermore, the greater the dissimilarity in tree community composition (turnover) between any two sites the greater the dissimilarity in ant community composition between these same sites. However, most of the explained variation in ant species richness and turnover was due to the joint influences of the environmental and spatial factors on tree species richness and turnover. Ants and trees shared similar environmental correlates of species richness and turnover, including especially net primary productivity, which in our study region is positively correlated with latitude. Congruent patterns of ant and tree diversity thus appear to have aroused because these two taxa are influenced similarly by environmental and spatial gradients. Nevertheless, we caution against the use of trees as surrogate of ant diversity patterns in Neotropical savannas, given that the observed spatial covariation in species richness and turnover was not strong to the point that tree diversity can reliably predict ant diversity patterns.