Odorous house ants: "drivers" or "passengers" of ecological change?

Invasive ants are often cast as “drivers” that cause ecological change or “passengers” that do not cause but benefit from ecological change. Natural colonies of odorous house ants (Tapinoma sessile) are thought to be subdominant and have little to no effect on neighboring ant species. In contrast, large urban supercolonies are thought to be dominant with a negative effect on resident species’ abundance and diversity. Our multi-habitat ant survey investigated this hypothesis and aids in understanding how Tapinoma sessile transitions from natural to urban environments. Ant community dynamics were measured in natural, semi-natural, and urban environments with comparisons made between plots with odorous house ants present and absent. We inspected all debris inside sampled plots and determined the number of species and colonies. Data was processed uncovering differences of ant community dynamics. Species diversity and abundance was high in natural and semi-natural settings with little difference between plots with or without Tapinoma sessile. When habitat transitioned into an urban landscape, both species diversity and abundance were significantly lowered with no significant effect from odorous house ant presence. Within the urban habitat, Tapinoma sessile presence further decreased ant diversity and abundance. These results support a quantifiable proportion of both “driver” and “passenger” roles for the odorous house ant in context of the urban environment.