Background/Question/Methods Non-native species introductions are becoming increasingly common. We know remarkable little about the long-term consequences of the novel pressures invaders impose on the native species they encounter. In addition to being critical to the effective management of invaders, this information provides valuable insight into processes that structure communities and permit species coexistence. The red imported fire ant, Solenopsis invicta, is an invasive species of potential global consequence. I took advantage of the well-documented spread of fire ants across the USA, using a combination of field studies and museum specimens to examine how interactions between this novel antagonist and a native lizard species change across invasion time. I examined the behavioral response to fire ants of adults and naive juveniles from sites with different histories of fire ant invasion. In addition, I assessed how limb morphology affects escape behavior and changes across time since fire ant invasion.

Results/Conclusions Fence lizards, Sceloporus undulatus, co-occur with fire ants across much of their invasive range, and occupy similar habitats. Attacks by fire ants on fence lizards are common and can be lethal: as few 12 ants can kill an adult lizard within a minute. I found that fence lizards have adapted to this novel threat, employing strategies that improve their chances of surviving aggressive encounters, within 70 years of invasion. Adult lizards from populations invaded by fire ants longer ago are more likely to behaviorally respond to fire ant attack than those from naive or recently invaded sites. Lizards from these populations also have relatively longer hind limbs, which increase the effectiveness of this behavior for removing attacking ants. These data contribute to our growing awareness that ecological invasions can prompt adaptive responses, altering the nature of interactions between invaders and the natives they contact.