The direct and indirect effects of the red imported fire ant (Solenopsis invicta) on seed fate in the longleaf pine ecosystem

Abstract

AbstractInvasion of non-native ants potentially disrupts natural relationships of native ants and ant-dispersed plants. These relationships may be affected directly through seed collection, or indirectly though impacts on the native ant community. Solenopsis invicta (the red imported fire ant), a widespread invasive of the southeastern United States, negatively impacts human health, agriculture, and wildlife. The impacts of S. invicta on native plant communities are less understood, partially because the invasions are usually coupled with human disturbance of soil or vegetation. The longleaf pine ecosystem is one of the few native communities successfully invaded by S. invicta. In a natural stand of longleaf pine with native groundcover we determined the fate of seeds collected by S. invicta, and the change in the ant community and seed removal due to disturbance by timber harvesting activities. We used cafeteria-selection trials with seeds of native plants to determine rates of seed removal. We presented S. invicta with dyed elaiosome-bearing seeds and recovered seed in middens above ground, and we sampled nests below ground with a wax cast. To examine changes in the ant community following disturbance, we sampled the ant community before and after timber harvest using pitfall traps and observing seed removal.We found that S. invicta preferentially collects myrmecochorous (elaiosome-bearing) seeds. We recovered approximately 30 percent of the dyed seed on the surface in midden piles of which only 17 percent had elaiosomes removed. However, this response varies seasonally. No seeds were recovered in the fall, suggesting that S. invicta is either consuming or storing more seeds prior to cold weather. We recovered few seeds in the nest castes. Initial ant community composition sampling resulted in 24 species. S. invicta was strongly dominant in most plots, and removed 83% of all seeds taken by ants.