Biogeographical and ecological factors affecting the altitudinal variation of mountainous communities of coprophagous beetles (Coleoptera: Scarabaeoidea): a comparative study

The altitudinal variation in the richness and composition of communities of coprophagous beetles in a mountainous landscape in Mexico is analyzed and the results obtained are compared with those of similar studies carried out in other parts of the world. Two nonexclusive processes are proposed as responsible for the assemblage of mountain fauna: horizontal colonization by elements originating from lineages distributed at higher latitudes and vertical colonization by lineages distributed at the same latitude but at different altitudes. The current analysis supports the hypothesis that when the horizontal colonization dominates, mountain faunas show a clear altitudinal substitution between large taxa with different evolutionary histories (e.g., Scarabaeinae and Aphodiinae) and the gradient of reduction in species richness is attenuated. This occurs in mountains of different continents and depends primarily on the degree of isolation and general orientation of the mountain ranges. Conversely, when vertical colonization dominates, mountain faunas show only slight altitudinal substitution, and the reduction in richness is greater.