NEW PAPER OUT! Testing effects of invasive fire ants and disturbance on ant communities of the longleaf pine ecosystem

1st pub for 2021 was just published in Ecological Entomology. This manuscript was a few years in the making as Julian Resasco and I originally talked about this back in ~2018. After a few job changes and moves, I am happy to say we finally finished it up!

Broadly, we were interested in how disturbance and invasive fire ant removal affected native ant communities. We took advantage of a framework proposed by MacDougal and Turkington that posited different ways invasive species could be characterized, either as “drivers” or “passengers” of change. The ‘driver’ model posits that species interact strongly and that native species are limited or excluded by competition with invasive species. Under this scenario, removal of an invasive species should increase native species richness and abundance. In contrast, the ‘passenger’ model posits that communities are primarily structured by factors other than interactions with invasive species (e.g. habitat disturbance) and that those factors are more beneficial to invasive species than native species. Under the ‘passenger’ model, removal of invasive species should have relatively little impact on native species.

But we also added a twist, an “interacting driver” model that was proposed as an alternative to the strict interpretations of “driver” and “passenger models” (Didham et al. 2005). The “interacting driver” model suggests additive or synergistic effects of habitat disturbance and invasive species that combine to reduce native species richness and abundance. Under this model, removal or reduction in abundance of invasive species should result in partial recovery of some native species.

To test these different hypotheses, 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. In doing so we found some interesting results. First, fire ant abundance in removal plots averaged 42% lower in pitfall traps and 95% lower on baits compared to unmanipulated, control plots (Fig. 1). No difference was found between disturbance and control plots though.

Second, species richness of co-occurring ants also decreased 42% in removal plots (Fig. 2), with significant changes in community composition. And again, no difference was found between disturbance and control plots.

Third, fire ant diet breadth—measured using carbon and nitrogen stable isotopes—increased up to 4.7‐fold in soil disturbance + removal plots. This last result is intriguing as it may suggest fire ants in removal plots consumed a greater variety of prey items and likely competed for resources with more co-occurring species.

Combined, 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. However, further recovery of native ants may be limited by persisting, landscape‐level effects of fire ants suppressing co‐occurring ants below historical levels.