Diverging facets of grassland ant diversity along a Mediterranean elevational gradient

1. We address associations of taxonomic diversity (TD), functional diversity (FD), and phylogenetic diversity (PD) of ant assemblages with gradients of elevation to assess whether energetic limitations or deterministic or stochastic niche-building processes are more relevant to the assembly of communities. 2. We sampled ant assemblages using pitfall traps in grassland habitats along an elevational gradient of 1712 m in the Guadarrama Mountains of Central Spain. The relationships of alpha and beta diversity metrics with soil temperature, productivity, elevation, and geographical distances were examined with generalised additive (mixed) models. 3. The facets of diversity showed strong and partially coincident responses to the gradients, but the responses and the similarities among them weakened or disappeared when the effects of species richness were factored out. TD and FD changed roughly in a similar manner with elevation and productivity, but PD did not show clear responses to those factors. Taxonomic and functional richness increased with productivity and decreased with elevation. Mean pairwise functional and phylogenetic dissimilarities did not change along the gradients. Elevation and productivity gradients accounted for much of the beta TD among assemblages but only explained a moderate variation of functional traits and phylogenetic relationships, while geographical distances were more explanatory of beta PD. 4. The partial redundancies among facets of diversity suggest that the spatial variation of diversity is mainly related to the sheer number of species. However, both environmental filtering and limiting similarity could be acting in concordance to reduce the number of species present in communities.