Assessing the impacts of invasive species can be difficult. One major reason for this is that, in the case of many biological invasions, we lack appropriate sampling or data from before the invasion. In most cases, we don’t know an invasive species is going to arrive, or what aspects of ecology it might impact in the area it is invading. For my doctoral research, I studied the impacts of invasive fire ants on native fence lizards in Tracy Langkilde’s lab at Penn State. Tracy’s work has shown that lizards in areas invaded by fire ants have higher behavioral responsiveness to ants (they twitch and flee from ants more), and have longer hind legs and higher stress responsiveness, which support this change in behavior and make it more effective. However, it has proven difficult to rule out that the differences we see between lizards from sites with and without fire ants were not due to patterns that might be present across the entire range of fence lizards.
In this paper, we conducted sampling across the latitudinal range of fence lizards, from Mobile, AL in the south to Pennsylvania in the north, and showed that the patterns in these traits are significantly different in areas invaded and uninvaded by fire ants. We were also able to integrate data from museum specimens to show that current patterns of hindlimb length are different from historical ones before fire ant invasion. These results suggest that fire ants have changed large-scale patterns in multiple fence lizard traits at sites hundreds of miles apart, all in less than 80 years. We find this exciting, because it shows that invasive species can have powerful impacts, but also that, at least in some systems, adaptive responses to invaders can occur relatively quickly and across a variety of traits.
Another great aspect of this work was the involvement of Mark Goldy-Brown, an Honors student at Penn State. Mark helped with all aspects of the project, including design, fieldwork, and writing the paper, even as he was conducting his own linked honors thesis examining geographical variation in how fire ant venom impacts fence lizards (stay tuned for more that!).
Thawley, C.J., M. Goldy-Brown, G.L. McCormick, S.P. Graham, and T. Langkilde. Early View. Presence of an invasive species reverses latitudinal clines of multiple traits in a native species. Global Change Biology.