Forest‐Water Ecotones: Flooding Impacts on Ant Species Distribution

ABSTRACT Natural ecotones between forest and lake‐swamp succession impose severe environmental filters for ant fauna, compared to adjacent forest habitats. This filter effect may be more severe for soil than canopy fauna. We tested this hypothesis by investigating the patterns of species occurrence, richness and composition of soil and canopy ants in forest and lake‐swamp ecotones in a tropical river basin. We established two transects (250 m) at each site, one placed in the ecotone (i.e., flood zone) and the other inside the adjacent forest. Although upper and lower river basin had totally different ant species composition, the species occurrence, richness and composition distribution between habitats followed a similar pattern for both altitudes. Occurrence of soil ants and species richness was similar between interior and ecotone. The occurrence and species richness of canopy ants were both higher in the ecotones than in the forest interior. Ant species composition was similar between the ecotone and adjacent forest, for both soil and canopy fauna, and the ant species composition was different between seasons (dry and rainy) and between canopy and soil fauna. Most importantly, the environmental filter imposed by the ecotone and its unpredictable habitat conditions favoured fewer but opportunistic species, which drove the higher occurrence in these habitats. The years we studied were particularly dry and had a substantial decrease in lake depth. Hence, the abilities of species to best use unpredictable resources from the natural succession on the new dry grounds might have been defined by omnivorous, opportunistic and numerically dominant ants. The abiotic particularities of forest‐water ecotones are important in the temporal dynamics of ant species assemblages. Fluctuations in water dynamics can restrict soil assemblages, but subtle changes in soil flooding also affect canopy fauna and can have unpredictable effects due to intensified variations in seasonal dynamics.