Water-energy dynamics, habitat heterogeneity, history, and broad-scale patterns of mammal diversity

Abstract

Numerous hypotheses on diversity patterns are often presented as if they were mutually exclusive. However, because of multicollinearity, correlational analyses are not able to distinguish the causal effects of different factors on these patterns. For this reason, we examine the interrelationships among current climate, habitat heterogeneity and evolutionary history by partitioning the variation in both total and non-volant mammal species richness in the Iberian Peninsula. Thus, it is possible to determine the variation accounted for by each one of these three components that is not shared by the others, and the respective overlaps. More specifically, we hypothesize that (H1) in warm temperate zones, a small increase in the available energy has strong negative effects on mammal richness if water availability is limiting; (H2) there are functional relationships between woody plant species richness (WOOD) and the richness of mammal species; (H3) there is a signal of evolutionary history in contemporary patterns of species richness, and (H4) mammal richness and the historical variable mean root distance (MRD) respond to the same driving forces. Additionally, we also test for spatial autocorrelation. We found a sharp nonlinear decrease in mammal richness with increasing energy and a monotonic increase with increasing water availability. Moreover, an interaction term between these two climate factors appeared to be statistically significant, so H1 could not be rejected. WOOD remained significant after partialling out both current climate and MRD at the family level (MRDf), supporting H2. The relationship between mammal diversity and MRD averaged by species richness was found to be spurious, but there appeared a significant historical signal using MRDf (this supports H3). The overlaps among these factors are consistent with H4 and suggest that water-energy dynamics have probably been active drivers throughout evolutionary history with habitat heterogeneity, and biotic interactions playing an important role.