OOS 40-9 - The impact of a pesticide, pendimethalin, on interspecific competition between two Daphnia species

Thursday, August 9, 2012: 10:50 AM
B113, Oregon Convention Center
Richard A. Erickson1, Jessica L. Oates2, Todd A. Anderson2 and Stephen B. Cox3, (1)Upper Midwest Environmental Sciences Center, United States Geological Survey, La Crosse, WI, (2)The Institute of Environmental and Human Health and Department of Environmental Toxicology, Texas Tech University, Lubbock, TX, (3)Department of Environmental Toxicology, Texas Tech University, Lubbock, TX

Anthropogenic chemicals occur ubiquitously throughout the environment, impacting communities and ecosystems. Traditional ecotoxicology has examined toxicant effects at the individual level under acute exposure conditions, and population level studies have only recently been incorporated into ecotoxicology. These studies increase the environmental realism of ecotoxicology, but fail to include community level effects. We examined how toxicants affected competition between Daphnia manga and D. pulex over a 24-day period in laboratory conditions. Three doses were used based upon a 48-hr dose-response curve for D. pulex: a control, a low concentration (10% of the LC50), and a high concentration (the LC10). We compared the effects of the herbicide pendimethalin on Daphnia populations within monocultures and bicultures through time. Our results were then incorporated into a matrix population model.


We found that both doses of pendimethalin had minimal impacts on populations within the monoculture treatments. In contrast, both doses of pendimethalin changed the competitive ability between the two species. Under control settings, D. pulex outcompeted D. manga. Under the low dose exposure, both species coexisted. Under the high dose exposure, D. manga outcompeted D. pulex. Thus, D. pulex, the more sensitive species, lost its competitive advantage to D. manga when pendimethalin was present.  These findings demonstrate how pesticides may facilitate competitive coexistence, similar to the presence of predators. Furthermore, our study provides an example of how quantitative ecology and ecological theory may be incorporated into ecotoxicology.