Forest fragmentation in central Amazonia and its effects on litter-dwelling ants

We assessed responses of ants nesting in twigs in the litter layer to habitat changes associated with forest fragmentation in central Amazonia. Ants were collected along transects located at nine distances (5, 20, 40, 60, 100, 200, 300, 400, 500 m) from the edges of two isolated 100-ha fragments and two continuous-forest sites. In total, 2880 m2 of litter were examined for the presence of ant colonies. We detected a significant decrease in litter depth with increasing distance to forest edge, and an increase and then decrease in the average diameter-at-breast-height (DBH) of large trees (DBH gtoreq 10 cm), and in tree basal area. Distance to forest edge significantly affected ant species composition and this effect was partly attributable to variation in litter depth. With the exception of one fragment, no significant changes in ant nest densities or species richness were found with increasing distance to forest edge. However, species richness of ants was greater in continuous forest than in both fragments. Furthermore, most species (65.8%) had greater nest densities in continuous forest. These results suggest that edge and isolation effects both play a role in structuring litter-dwelling ant communities in Amazonian forest remnants.