Using the red-imported fire ant to study invasive species removal and reinvasion

Abstract

Invasive species are a major driver of native species declines, frequently resulting in a reduction of ecosystem function. Though control of invasive species is often beneficial, it can create other ecological issues. However, studying the results can give insight into the benefits of removal and most effective management techniques. A model invasive species to test the effects of removal is the red-imported fire ant (Solenopsis invicta, hereafter RIFA), which depredates and competes with native species. We hypothesized that following removal, RIFA would recolonize treated areas from untreated borders, resulting in reinvasion and higher densities due to elimination of competition from native species that would also be extirpated by treatments. To test our hypothesis, we compared RIFA relative abundance on large sites (>400 ha) treated with a granular insecticide (Extinguish Plus, Central Life Sciences, Schaumburg, IL) in southwest Georgia, USA. Extinguish Plus effectively removed RIFA, but the treated sites were reinvaded approximately 14 months after treatment with higher densities of RIFA than on untreated areas, potentially reflecting release from competition from native ants removed by treatments. Invasive species removal may elicit a rapid recolonization via a density-dependent response mechanism and potentially increase abundance of the target species. Management strategies integrating temporal and spatial replication of control measures and multiple management techniques will be most successful in controlling invasive species.