Understanding the factors that influence escape responses can provide valuable insight into the processes that structure communities and permit species coexistence. Non-native species introductions are becoming increasingly common, and can impose novel threats to the native communities they invade. Populations exposed to such environmental perturbations often exhibit elevated physiological stress levels (measured as levels of circulating glucocorticoids). Native fence lizards, Sceloporus undulatus, co-occur with fire ants, Solenopsis invicta across much of their invasive range. Attacks by fire ants on fence lizards are common and can be lethal. I conducted staged encounters between fence lizards and fire ants in the field to assess the role that physiological stress levels and prior exposure of native lizards to this invasive fire ants plays in driving lizard escape behavior.

Results/Conclusions

This study suggests that population-level exposure to fire ants and the physiological stress response to ant attack drive the behavioral response of lizards to fire ant attack. Lizards from fire ant invaded areas are more likely to respond to fire ant attack than lizards from uninvaded sites. Lizards from both sites exhibit elevated levels of the stress hormone, corticosterone (CORT) following attack by fire ants. CORT appears to be driving the behavioral response of fence lizards to fire ants; lizards that have their circulating CORT levels artificially elevated are more likely to respond to fire ant attack. This suggests that, rather than being a cause for concern, elevated levels of physiological stress within invaded populations may be playing an important role in driving the adaptive response of natives to novel threats.