Testing effects of invasive fire ants and disturbance on ant communities of the longleaf pine ecosystem

Authors: Roeder, Karl; PENUELA USECHE, VIVIANA - Florida Department Of Environment; LEVEY, DOUGLAS - National Science Foundation (NSF); RESASCO, JULIAN - University Of Colorado

Submitted to: Ecological Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/11/2021
Publication Date: 3/23/2021
Citation: Roeder, K.A., Penuela Useche, V., Levey, D.J., Resasco, J. 2021. Testing effects of invasive fire ants and disturbance on ant communities of the longleaf pine ecosystem. Ecological Entomology. https://doi.org/10.1111/een.13033.
DOI: https://doi.org/10.1111/een.13033

Interpretive Summary: Invasive species and habitat disturbance are among the most important drivers of biodiversity loss. However, it is hard to determine if invasion or disturbance, alone and/or combined, are the true cause. In this study, we tested a variety of hypotheses to answer this question using the red imported fire ant, a devastating invasive species that is common in the southeastern United States. We randomly assigned treatments of (1) unmanipulated, (2) soil disturbance, (3) fire ant removal, and (4) soil disturbance + fire ant removal to experimental blocks and measured how native ant communities changed. After two years, fire ant abundance was up to 95% lower in removal plots compared to unmanipulated, control plots. The number of native ant species also decreased 42% in removal plots, but the abundance of some co-occurring species increased. Soil disturbance alone did not affect ants. While non-target impacts of the fire ant removal treatment complicate interpretation, our results suggest reducing fire ants allowed the partial recovery of some native species. Further recovery of native ants may be limited, though, by landscape-level effects of fire ants suppressing co-occurring ants below historical levels.

Technical Abstract: 1. Invasive species and habitat disturbance are among the most important drivers of biodiversity loss and ecological change. Their individual effects, however, are difficult to disentangle because invasion and disturbance are often intimately linked. Here we test alternative hypotheses to determine if the invasive red imported fire ant, Solenopsis invicta, is a “driver” or simply a “passenger” of ecological change in a longleaf pine ecosystem. 2. We randomly assigned treatments of (1) unmanipulated, (2) soil disturbance, (3) fire ant removal, and (4) soil disturbance + fire ant removal to experimental blocks and measured how ant communities changed over two years in thirty-six 15-m2 plots. 3. Fire ant abundance in removal plots was on average 42% lower in pitfall traps and 95% lower on baits compared to unmanipulated, control plots. Co-occurring ant species richness also decreased 42% in removal plots with significant changes in community composition. Soil disturbance alone did not affect ant communities. Fire ant diet breadth—measured using carbon and nitrogen stable isotopes—increased up to 4.7-fold in soil disturbance + removal plots (i.e. 0.84‰2 to 3.94‰2). 4. While non-target impacts of the fire ant removal treatment complicate interpretation, our results suggest fire ants follow an alternative “interacting drivers” model in which partial recovery of some species occurs when populations of an invasive species are reduced. Further recovery of native ants may be limited by persisting, landscape-level effects of fire ants suppressing co-occurring ants below historical levels.