Influence of topography on the distribution of ground-dwelling ants in an Amazonian forest

In this study we determined the effects of topography on the distribution of ground-dwelling ants in a primary terra-firme forest near Manaus, in central Amazonia. Ants were collected along stream valleys and on forest plateaus by using pitfall traps, sardine baits, and by extracting ants from litter samples. Although the number of species per plot (species density) did not differ between different topographic regions, in total, more species were recorded in valleys than on plateaus. Species evenness also tended to be greater in valleys than on plateaus. Dominant species were relatively rare in valleys, possibly because litter, an important food resource and nesting site, was present in smaller quantity in valleys than on plateaus. Ant abundance was about two times greater on plateaus than in valleys, whereas nest densities were nearly three times higher. Part of this difference was attributed to differences in soil texture and vegetation structure associated with topography. Ordination of plots according to ant species composition showed a separation between valley and plateau plots, These results indicate that local topography promotes heterogeneity in species distribution, and explains part of the observed and strong, within-forest variability in the abundance and diversity of ground-dwelling ants.