Ant Diversity and Stratification in an Amazonian Rainforest

This study focuses on species occupying the three strata of an Amazonian rainforest: the ground and leaf litter, the understorey and the canopy. We employed only two sampling techniques: Winkler extraction for ground-dwelling ants and direct observations for understorey and canopy species on large branches cut off by a climber. We identified 494 ant species from 10 subfamilies and 77 genera over ≈3.0 ha (Chao1 = 607 species; 95% CI: 566-670 species). Although we found fewer arboreal ants compared to approaches using insecticide fogging, this study confirms similarities between the ant diversity in Amazonian and Mesoamerican rainforests. The functional traits of these ants (i.e., diet, nest-site preference, population size of the colony) allowed us to identify seven clusters. Cluster 1 is a "hodgepodge" grouping arboreal or ground-dwelling species with different-sized colonies (76 species). Cluster 2 primarily includes small colonies of ground-nesting generalist feeders (142 species). Cluster 3 comprises all arboreal species from the understorey inhabiting myrmecophyte domatia or palm trees plus arboreal species with medium-sized colonies (37 species). Cluster 4 includes all territorially dominant arboreal ants plus one ground-dwelling species (21 species). All fungus-growing species belong to Cluster 5, which also contains ground-nesting generalist feeders and generalist predators (148 species). All doryline army ants are grouped in Cluster 6 along with one ponerine known for its nomadic behavior (15 species). Almost all specialized predators belong to Cluster 7 (55 species); however, Cluster 5 includes two ponerine species that prey exclusively on termites. Based on a nonmetric multidimensional scaling (NMDS), we confirmed that the position of these clusters corresponded fairly well to the three forest strata. Thus, analyzing functional traits enables the trophic position of most ants and their place in the vertical strata of Neotropical rainforests to be determined.