Seasonal fluctuation of groundwater level influences local litter‐dwelling ant richness, composition, and colonization in the Amazon rainforest

Abstract

Groundwater fluctuation follows the rainfall regime and is a natural source of disturbance by limiting the soil volume available for ant nesting. However, in areas with shallow water‐table unpredicted floods are more frequent, which may also affect the distribution of litter ant species. Here, we evaluated the behavioural responses and diversity changes of litter‐dwelling ants related to groundwater level fluctuation in the central Amazon tropical rainforest. The natural occurrence of vertically stratified litter (above the ground level) accumulated at the base of stemless palms was a control sample in a series of paired samples. We used baits to measure ant activity and Winkler extractors to measure ant diversity in 10 riparian plots during the rainy (shallow water‐table) and dry (deep water‐table) season. We also added processed litter to count the number of new colonies found in both habitats. We found fewer ant species and less occurrence during the rainy season. The assemblage composition was more heterogeneous during rainy season compared to same locations during dry season. However, ant activity such as recruitment and investment in resource monopolization showed an opposite pattern. The investments in reproduction followed ant recruitment to baits, with more colonies found in the leaf‐litter during the dry season. All changes were strongly decreased or absent from the control locations. Our results suggest that unpredicted floods mediated by water‐table fluctuation may act as a disturbance to most ant litter species but may favour resource monopolization and litter colonization.