Invasion by red imported fire ants depletes soil microarthropod communities in agricultural systems

Biological invasion is one of the major challenges to changing ecosystems worldwide. Red fire ants are a prime example of invasive soil animals. However, the impacts of their invasion on the native soil animal communities are still poorly understood. Here, we investigated how the biomass and diversity of soil microarthropods (incl., Collembola and Acari) vary between areas affected by red fire ants at different degrees (i.e., OA, occurrence area, 0–20 m from the nest; PCA, prevention and control area, 20–50 m; POA, potential occurrence area, 50–100 m). We also tested whether the potential effects of ant invasion on other animals are associated with changes in soil properties in the invaded areas. Our results showed a decline of 64% in species richness, 74% in density, and 72% in biomass of microarthropods in OA in comparison with POA. This reduction was mainly driven by the decrease of Acari, while no reduction in Collembola biomass was observed. Despite soil properties being significantly different between ant-impacted areas, structural equation models indicated that the direct association of invasion with microarthropod communities is stronger than the indirect association mediated by soil properties. Therefore, we consider that direct biological interaction is more likely the major mechanism behind the observed changes in microarthropod communities. The effects of red fire ants were different among taxonomic and functional groups, with litter-dwelling Collembola, Oribatida, and Mesostigmata (Acari) affected more negatively than soil-dwelling and surface-dwelling Collembola. Further, red fire ants affected the turnover component of beta-diversity (i.e., replacement of species) for both Collembola and Acari. However, the impact on the nestedness component, which is related to species local extinction and population decline, was only detected for Acari. Our study shows that red fire ant invasion is associated with the depletion of soil microarthropod community, and especially highlights that Acari are more vulnerable to this invasion compared to Collembola. The divergent response between different taxonomic and functional groups of microarthropods and the consequent shift in microarthropod communities may have important significance to soil ecological functioning in the impacted areas.