Date of Award

12-2004

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Ecology and Environmental Sciences

Advisor

Eleanor Groden

Second Committee Member

Francis A. Drummond

Third Committee Member

Michael Kinnison

Abstract

In the early to mid-201h century, Mvrmica rubra Latreille established in various communities in Maine, mostly along the coast. Since its establishment, the ant has spread both locally via vegetative colony budding and regionally via human commerce to no fewer than 30 Maine communities, including one inland site. Studies were undertaken in the summer of 2002 to address questions of the ants' population structure in its introduced range by testing for intercolony aggression within and between local infestations. Using captive nests maintained in their original nest soil, M. rubra was tested against its close neighbors, neighbors of lorn within the same infestation, and at two locations within a distinct infestation elsewhere on the island. Aggressive behaviors were quantified, and results suggest a multicolonial population structure, with ants tolerating their close neighbors (perhaps fragments of their own colony), showing measurable aggression toward their 1Om neighbors, and significantly more aggression again toward distant neighbors from which they were separated geographically at the outset. Pitfall and Berlese funnel sampling in four paired sites in Acadia National Park in 2002 showed little impact of M. rubra on the resident (non-ant) arthropod community, with the exception of a significant increase in isopod abundance. Impacts on the native ant fauna were severe, reflecting almost complete displacement and a significant reduction in species richness and diversity. Independent sampling of the homopteran community (tended by M. rubra and native ants for their honeydew exudates) showed an enhanced richness and abundance of several groups where M. rubra was present. Proportionally fewer homopterans were left untended within invaded habitat, suggesting that these insects are "ant-limited" and confirming our results that M. rubra may enhance such populations. Finally, a total of 27 aggression assays against nativelresident ants in Acadia National Park were performed in an attempt to quantify and characterize behavioral interactions between M. rubra and the native ant community. On average, M. rubra was able to quickly dominate the native foragers and displace them from baits, though some species were more adept at defense, generally by virtue of a well developed sting or chemical spray. A separate experiment testing discovery time and recruitment at the boundary of a local infestation showed that M. rubra foragers discover and recruit more quickly to a food resource. Taken together, these findings suggest that M. rubra, by virtue of its numerical dominance, has broken the "dominance-discovery" trade-off that serves to partition food resources, allowing native ant coexistence (Fellers, 1987).

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