Dung beetle β‐diversity across Brazilian tropical dry forests does not support the Pleistocene Arc hypothesis

Abstract

Tropical dry forests (TDFs) are one of the most threatened ecosystems worldwide. Two hypotheses have been proposed to explain the origin of TDFs in South America: the Amazonian TDF hypothesis and the Pleistocene Arc hypothesis (PAH). There is a need to evaluate the distribution patterns of different organisms across the TDF distribution. We tested the following hypotheses: the species composition is determined by historical‐evolutionary events, and therefore, the TDFs have a similar species composition as predicted by the PAH. Alternatively, the species composition is determined by recent ecological processes, and therefore, the TDFs have a sharing of species to their respective adjacent dominant habitat, with no support for the PAH. We expect that climatic factors drive the species richness, abundance and species dissimilarity (β‐diversity) between TDFs and adjacent habitats across the latitudinal gradient. We sampled dung beetles across six Brazilian states in TDF fragments and adjacent dominant habitats and obtained the climatic conditions across the gradient. We used the β‐diversity partition and generalised linear models to test our hypotheses. We sampled 8,625 dung beetles representing 102 species. Sorensen dissimilarity was higher among TDFs than between TDFs and adjacent habitats and was mostly due to the substitution of species. Annual mean temperature had a positive effect on abundance in TDFs but did not affect species richness. Species substitution (Podani’s approach) between TDFs and adjacent habitats decreased with mean diurnal range of temperature, while nestedness patterns (Baselga’s approach) increased with annual precipitation. Depending on the approach used (Baselga’s vs. Podani’s), we can obtain different results across the latitudinal gradient. The composition and structure of dung beetle assemblages in TDFs are mostly determined by more recent regional‐to‐local ecological processes since each TDF has a unique evolutionary history and a different dung beetle species composition. Our results do not support the Pleistocene Arc hypothesis.