Historical and ecological determinants of dung beetle assemblages in two arid zones of central Mexico

This work focuses on coprophagous beetles (Scarabaeinae and Aphodiini) from two arid zones located in the center of Mexico: Barranca de Metztitlán, Hidalgo, and Zapotitlán-Salinas, in the high zone of the Tehuacán-Cuicatlán depression. The first site has a rich representation (in terms of species, individuals, and biomass) of beetle fauna from the dry Mexican Altiplano, whereas the beetles from Zapotitlán correspond to a reduced subset of the fauna from the Balsas and the middle and lower zones of the Tehuacán-Cuicatlán depression. Although flowering plants from both arid zones show the same biogeographical affinities, there is a significant contrast in the degree of endemism, with the highest plant endemism in the Tehuacán-Cuicatlán Valley, and no a single endemic species within beetles. In this work, we propose a biogeograpical-historical explanation for this contrasting phenomenon. Beetles assemblages from both zones included in this study are characterized by the marked dominance, both in terms of individuals and biomass, of one species of the genus Canthon. Success of the dominant Canthon species can be explained by their thermoregulation mechanisms, whereas dominance of other medium-sized species could be associated with the availability of trophic resources as a result of anthropic influence.