Distribution of epigeic and hypogeic ants (Hymenoptera: Formicidae) in ombrophilous forests in the Brazilian Amazon

Abstract

In the Amazon basin, ants are often associated with environmental or edaphic factors. However, these associations may vary between the epigeic and hypogeic strata. Here, we investigated differences in richness and composition of epigeic and hypogeic ant assemblages along an environmental gradient in the Brazilian Amazon. The four studied sites cover different topographic and soil characteristics. We sampled 25 plots of 250 m2 using 10 samples of epigeic pitfalls and 10 samples of hypogeic pitfalls installed at two depths (10 and 30 cm). The pitfalls remained in the fi eld for 48 hours. In the same plots, soil clay content and terrain altitude were also measured. We collected 219 species or morphospecies, of which 14 were exclusively hypogeics. We found higher local richness in the epigeic compared to hypogeic assemblages. We also found an interaction between clay content and strata for ant species composition. Overall, the species turnover was related to clay content, but the eff ect depended on the strata, with hypogeic fauna being more heterogeneous, compared with epigeic fauna. Despite the relationship between clay content and ant´s assemblage’s composition, we did not find strong environment predictors for both strata, which suggests that other factors may structure ant assemblages in these sites. This reinforces the need for studies to defi ne which environmental gradiente determines the distribution of Amazonian epigeic and hypogeic ants.