Non-native ant invader displaces native ants but facilitates non-predatory invertebrates.
Many invasive ants, such as the European fire ant (Myrmica rubra), are particularly successful invaders due to their ability to form multi-nest, multi-queen 'supercolonies' that appear to displace native invertebrates in invaded regions. Myrmica rubra has invaded many areas in the Northeastern United States, including Western New York. Myrmica rubra invasion corresponds with decreases in native invertebrates, particularly ants, an effect which may be attributable to direct displacement, or because M. rubra prefers habitat unsuitable for native ants. We surveyed Western New York parklands to investigate native ant and non-ant invertebrate abundance in M. rubra-invaded and uninvaded areas. We then tested these observations with an ant pesticide treatment targeting M. rubra to investigate the direct impacts of M. rubra on the native ant and invertebrate community. A consistent, negative relationship was found between M. rubra and native ants in both the observational and experimental research, and native ant species only appeared in the pesticide-treated plots (with reduced M. rubra abundance). These data strongly suggest that M. rubra actively displaces the native ants with invasion instead of segregating by habitat. Myrmica rubra effects on non-ant invertebrates appeared more nuanced, however, in both the observational and experimental research. The absence or removal of M. rubra corresponded with decreased predatory invertebrate populations and increased non-predatory invertebrates. It appears that M. rubra has altered invertebrate communities in Western New York. Native invertebrate communities may be able to rebound with time, but our data suggest native recovery unlikely without management intervention.