Ant assemblage and morphological traits differ in response to soil compaction

Soil compaction, a process that decreases the free space among soil particles and hinders the underground movement of soil organisms, is one of the increasing impacts of mankind on the world’s ecosystems. We investigated the responses of subterranean ants to soil compaction by testing the following predictions: (i) soil from a trail is more compressed, leading to (ii) a decrease in species richness and a selective shift in ant assemblage composition, which is made up by (iii) species with a smaller body size that can apply a greater relative strength to move through soil particles. We carried out this study in and outside of a recreational ecology trail in a forest fragment in Viçosa, MG, Southeastern Brazil. The compaction was higher in the soil from the trail than outside of it. No change was observed in species richness, but soil compaction promoted a shift in ant assemblage composition, with ant size decreasing with an increase in soil compaction. However, ants did not appear to apply a greater strength to soil particles for moving in habitats with a high soil compaction. Overall, organisms at superficial soil layers appeared to be sensitive to even moderate human impacts that promote a filtering of the ant assemblage species composition, with small body size being a required trait