Early invasion dynamics of the Japanese pavement ant, Tetramorium sushimae, in the Saint Louis, Missouri metropolitan area

Invasive species are non-native species that undergo rapid population growth and incur significant biological costs. Worldwide, they are the second leading cause of species extinctions. Invasive ants are particularly destructive, constituting 5 of the world's 100 worst invasive species. A major push in the study of biological invasions has been to understand their incipient stages, because once thoroughly established, invasions are nearly impossible to eradicate. The Japanese pavement ant, Tetramorium tsushimae, is a recently discovered invasive species found throughout the St. Louis metropolitan area and one of the few successful early stage ant invasions known. The primary goal of this research is to use this species to understand how early biological invasions proceed by using methods in population genetics, animal behavior, and community ecology. The first chapter is a literature review on what is known about the early stages of ant invasions. The second chapter uses microsatellite variation measured from nests collected throughout the invaded range to quantify population genetic structure. I demonstrate that the invasion is likely the result of a single invasion event originating in St. Louis, MO and subsequently spreading through human-mediated and natural dispersal throughout the present range of Eastern Missouri and Western Illinois. The third chapter quantifies intra-specific aggression in North American T. tsushimae. The Japanese pavement ant demonstrates low levels of intra-specific aggression (i.e. unicoloniality) throughout the invaded range. Aggression is correlated to microsatellite genetic distance; aggression increases as nest pairs are less genetically similar. The fourth chapter addresses the ecological effect of the Japanese pavement ant on native ants by comparing community structure in invaded and uninvaded prairie and turf grass ecosystems. When paired with the results of an artificial introduction competition experiment, this research indicates that the Japanese pavement ant has a significant negative effect on native ant species. The Japanese pavement ant is a successful, unicolonial, and dominant invasive species that is being spread geographically through human activity. As a model system, this research can provide insight into the ecology and evolution of early stage ant invasions; thereby aiding in creating effective and efficient conservation policy.