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

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