The role of fire ants as seed dispersers in a native ecosystem

The red imported fire ant (Solenopsis invicta) is an aggressive invader that is negatively impacting native plant and animal communities as it spreads throughout the southeastern United States. The impacts of S. invicta on plant dispersal are of interest in the longleaf pine ecosystem, where it is feared that fire ants may become dominant, potentially depriving ant-dispersed seeds of native dispersers. This highly threatened ecosystem contains numerous elaiosome-bearing species and alterations in patterns of seed dispersal could influence the restoration potential of the diverse flora. Our study quantified the composition of the ant community in the longleaf pine ecosystem and examined the effectiveness of S. invicta as a seed disperser. Specifically, we trapped ants monthly for over one year to determine the relative abundance of fire ants and the relationship between fire ant dominance and ant community richness. We also observed removal of ant-dispersed seeds from caches to compare discovery time of the cache, as well as distance and destination of seeds removed, between fire ants and native ant species. Pitfall trapping efforts indicated no correlation between the abundance of fire ants and native ants, nor species richness, suggesting that at the densities of fire ants present at this site, fire ants are not competitively displacing native ants. Furthermore, seed removal rates and distance did not differ between native and fire ants, and fire ants were just as likely as natives to carry seeds into their nests, suggesting that fire ants may function similarly to native ants as seed dispersers.