Impacts of invasive ants on native ant communities (Hymenoptera: Formicidae)

The most commonly documented consequence of alien ant invasions is the displacement and local extinction of native ant species. However, several processes may lead to low native ant diversity in the presence of non-native species. Invasive ants may, indeed, competitively exclude native ants. Conversely, invasive ants may not be able to spread into diverse, competitively dominant native ant communities. Finally, complementary distribution of invasive and native ants may be non-interactive and instead driven by divergent responses to heterogeneous environmental factors. Here, I review studies of non-native ants that have associated negative impacts on native ant communities, discuss how native ant communities are reorganized in invaded habitats, summarize reports of vulnerable and resistant ant species, and examine evidence for mechanisms of reduced native ant diversity. Invasive ants are often, but not always, associated with lower native ant abundance, reduced species diversity, and randomly structured, homogenized native ant communities. Native ants are unlikely to co-occur with invasive ants 1) in habitats with environmental conditions suitable to and / or modified for the invader, 2) during the height of an invasion when an invading species is at its peak density, 3) when native ants are ecologically similar to the invading species and lack potent chemical defenses. Little evidence supports the biotic resistance hypothesis for native ants. Instead, suitable environmental conditions are primary determinants of the establishment and success of invasive ants. While invasive ants generally thrive in disturbed areas, many studies document the spread of invasive ants into undisturbed habitats and support the notion that invasive ants can drive declines in native ant diversity. More experimental studies are needed to explicitly test the importance of interactive and noninteractive processes in determining the spread of invasive ants and their impacts on native ant diversity.