The fields of toxicology and ecology are largely separate disciplines in the questions asked and the approaches taken. However, the two fields share a common goal of trying to understand how anthropogenic chemicals affect species and communities via direct and indirect food web effects. This common goal is especially strong for understanding how chemical stressors affect amphibian assemblages because of current conservation concerns over their global decline. Past studies of stress on amphibians have focused largely on the effects on single species under laboratory conditions. While this work has provided a great deal of excellent data, we ultimately wish to know what happens under more natural conditions. This proposal addresses these needs by using a series of field experiments that examine seven species of amphibians and common environmental stressor that are associated with amphibian declines. The work will focus on understanding how predators, and competitors interact with natural and anthropogenic stressors to affect aquatic communities. The broader impacts consist of training of graduate and undergraduate students (including under-represented groups). The benefits to society include a better understanding of how human stressors affect natural communities and global amphibian declines. Our results will be disseminated by the PI and students in journals, conferences, and the popular press. The experimental results will be developed into teaching modules for regional middle and high school teachers. Collectively, this research offers a great opportunity to advance our basic understanding of ecological systems and have a strong, positive impact on society.
Scientific merit The goal of this research project was to investigate the effects of common contaminants (i.e. pesticides) on the communities of species that live in wetlands. This project lasted 6 years and during that time we made a large number of discoveries that met and exceeded the original goals of the work. One focus of our work has been to examine the different pathways through a food web by which pesticides can potentially impact different species of aquatic organisms. In a series of studies, we found that low concentrations of an insecticide can initiate a chain of events that ultimately causes less food to be available tot tadpoles, which can cause substantial amounts of death. In related studies, we discovered that very low concentrations of pesticides can be highly lethal to amphibians when combined as mixtures. Our research has contributed a large amount of basic toxicology data (i.e. LC50 data) on the herbicide Roundup and the insecticide endosulfan. In doing so, we discovered that endosulfan can have dramatic lag effects, such that a standard 4-day test will often not accurately document the total mortality that tadpoles will experience just a few days later. We have also discovered that natural stressors, such as predators and competitors, can substantially alter the toxicity of some pesticides. This is a relatively unknown in aquatic animals. In addition to conducting research on pesticides, we also had the opportunity to begin some studies on the deadly amphibian fungus, known as the chytrid fungus. In a series of experiments, we examined potential interactive effects between the fungus, predators, competitors, and pesticides. Finally, our research has inspired a number of reviews papers and book chapters that examine the role of pesticides on aquatic organisms. Broader impacts During the years of this project, I have presented 43 invited talks and 25 conference talks. We have also trained a large number of post-docs, graduate students, undergraduate students, and high school teachers. For the past 4 years, we have conducted an annual High School Teachers Workshop, which brings in teachers for a week of training in how to do science and teach science.
