Abstract: Nearly half of the ant species present in a tropical forest are directly in contact with the ground for nesting or foraging, with evidence of vertical stratification among ground layers (i.e., surface, litter, and soil). How ants in each layer respond to environmental factors and to seasonality remains little studied. We hypothesized that ant species distribution varied spatially and seasonally among the three ground layers and that their distribution was distinctly affected by various abiotic and biotic factors. Ants were collected in an Ecuadorian premontane tropical forest and their distribution was analyzed spatio-temporally: vertically (between the ground surface, leaf-litter, and mineral soil, using pitfalls, Winkler, and soil cores), horizontally (every meter along a 100 m transect) and seasonally (between the dry and the rainy seasons). Four environmental parameters were measured every meter along the transect: canopy openness, slope, leaf-litter depth, and leaf-litter volume. Correlations between species distribution, richness, abundance, and environmental variables were calculated. Species richness was high, with 176 species collected along the transect. Our results show a clear vertical stratification, with distinct faunal composition in each layer and a strong seasonal effect. Stable distribution of several dominant species between seasons suggests a low nest relocation rate. During the dry season, higher ant richness and abundance were found in pitfall traps suggesting higher activity on the surface of the forest floor. Similarly, higher ant richness and abundance found in the soil during the dry season suggest the migration of drought-sensitive species downwards deeper into the soil. Species richness and dominant species distribution were related to distinct factors according to the layer considered; we found strong correlations between the quantity of leaf-litter and dominant ant species distribution and species richness in the leaf-litter layer, while no correlation was found with any factor in the soil layer. Our results show that ant faunal composition and the response of ants to environmental factors vary vertically at small spatial scale and seasonally, which emphasizes the importance of distinguishing layers in the ground matrix.

Preview not available.