Imported crazy ant extirpates imported fire ant, reduces and homogenizes grassland ant and arthropod assemblages

A recently introduced, ecologically dominant, exotic ant species, Nylanderia nr. pubens, is invading the Southeastern United States and Texas. We evaluate how this invader impacts diversity and abundance of co-occurring ants and other arthropods in two grasslands. N. nr. pubens rapidly attains densities up to 2 orders of magnitude greater than the combined abundance of all other ants. Overall ant biomass increases in invaded habitat, indicating that N. nr. pubens exploits resources not fully utilized by the local ant assemblage. At high density, as N. nr. pubens spreads, it eliminates the current ecologically dominant invasive ant, red imported fire ants (Solenopsis invicta). Compared to imported fire ant dominated habitat, non-ant arthropod species richness and abundance are reduced by invasion with impacts differing by trophic category. Further, N. nr. pubens reduces abundance and species richness of the remainder of the ant assemblage and does so in a non-random manner: impacting species with small sized workers much less than species with larger workers. Nest usurpation may drive this pattern. In these and other ant assemblages with a large exotic component, the exotics tend to be small bodied species. As a result, through a remarkable process of biogeographic homogenization, N. nr. pubens almost completely eliminates regionally distributed species, but leaves globally distributed species largely unaffected, thereby systematically favoring introduced over native diversity. This process may be general to ant assemblages with many exotic species colonized by opportunistically nesting, invasive ant species. S. invicta impacts wildlife and arthropod assemblage structure and is nearly ubiquitous in non-forested habitats of the Southeastern United States and Texas. Its displacement by N. nr. pubens has critical implications for the natural systems of this region.