UC Riverside

Ants have often been described as keystone species for the critical roles they play that contribute to ecosystem functioning. Evidence from Europe and Australia has improved our understanding of the impacts of disturbance, including pollution, on native ant communities. However, there is a lack of information available for North American ant communities. The overall goal of this dissertation was to assess the effects of selenium, a globally widespread element and environmental contaminant in certain regions of the U.S., on the survival, behavior and reproduction of the invasive Argentine ant, Linepithema humile. The findings of this research highlight the unexpected role of pollution to act as a potential barrier to range expansion for invasive ant species.

Chronic ingestion of four environmentally common forms of selenium at environmentally reported concentrations, were found to cause mortality among Argentine ant workers. The extent of mortality was found to be dependent on the form of selenium. In addition, mortality and bioaccumulation of selenium increased with the duration of exposure and concentration. Furthermore, Argentine ants were not deterred by lethal concentrations of selenium in the diet, regardless of background sucrose concentrations.

The transfer of selenium via a tri-trophic system was assessed. Aphid honeydew, a major component of the diet for Argentine ants in their introduced range, was found to serve as a route of selenium transfer to ant colonies.

Sub-lethal concentrations of selenium were found to impact reproduction for Argentine ant colonies, where colonies exposed to selenium sucrose diets experienced reduced queen fecundity, queen mortality, and reduced viability for offspring. Selenium did not alter the competitive ability of Argentine ant workers during interactions with the native species, Dorymyrmex bicolor, but sub-lethal concentrations did contribute to a longer food discovery time for the native species.

Native ant communities residing in a selenium-contaminated habitat were also documented. Ant species composition differed across sites, but selenium did not appear to have an overall impact on diversity. Ant concentrations differed by species, but were comparable to levels found among other arthropod trophic groups. Results suggest that these ants residing have evolved a high tolerance to this particular pollutant.