LAUSR

A successful invasion of novel habitat requires that non-native organisms overcome native abiotic and biotic resistance. Non-native species can overcome abiotic resistance if they arrive with traits well-suited for the invaded habitat or if they can rapidly acclimate or adapt. Non-native species may co-exist with native species if they require novel, underused resources or if they can out-compete similar native species. We investigated abiotic and biotic resistance to the progression of a Brachyponera chinensis invasion in the southeastern U.S. relative to the dominant native woodland ant ( Aphaenogaster ). We used observational data from long-term plots along the elevation gradient of the Southern Appalachian Mountain escarpment to investigate the patterns of B. chinensis invasion, and we used physiological thermal tolerance, aggression assays and stable isotope analysis to determine whether abiotic or biotic factors explained B. chinensis invasion. We found that B. chinensis exhibited an inflexible and relatively poor ability to tolerate cold temperatures, which corresponded with limited success at higher elevations in the Southern Appalachian Mountains. Though we found native ant resistance to B. chinensis invasion, it paled in comparison to the invasive ant’s ability to form huge, cooperating supercolonies that eventually eliminated the native ant. Without biotic resistance, susceptible native species may only be protected if they can tolerate abiotic conditions that the invasive species cannot. For Aphaenogaster species, high elevations and northern latitudes beyond B. chinensis ’ cold tolerance may be their only refuge.