Experimental evidence for weak effects of fire ants in a naturally invaded pine-savanna ecosystem in north Florida

1. Fire ants naturally invade some undisturbed ecosystems of high conservation value and may negatively impact co-occurring ants. 2. Over 3 years, fire ants were added and removed from a longleaf pine savanna ecosystem that naturally supports a low density of fire ants. Impacts on co-occurring ants were monitored using pitfall traps. 3. Treatments resulted in significant differences in average fire ant abundance across all plots only in the first year of the experiment. Fire ants had little discernible impact. The abundance and species richness of co-occurring ants in removal plots never differed from unmanipulated control plots. The abundance of co-occurring ants was very slightly lower and ant species richness was slightly higher where Solenopsis invicta Buren colonies were added, but neither contrast was significant. 4. The poor conditions in this habitat for many native ants may explain this outcome. More broadly, the impact of fire ants on ant assemblages still appears to be secondary and largely a consequence of human impacts on the environment.