Dr. Tim Stewart from Iowa State University's Department of Natural Resources Ecology & Management will be presenting this research as a part of the spring semester seminar series. The seminar will be located in E164 Lagomarcino Hall.
Abstract: Human-generated landscape changes have facilitated increased fish abundance in wetlands of the Iowa prairie pothole region. Invasive species of fishes (e.g., black bullhead) may cause declines in wetland condition by increasing water-column concentrations of nutrients and particulate matter, and by reducing abundance and taxonomic diversity of plants, invertebrates, and non-fish vertebrates. The primary objective of this study was to gain insight into fish impacts on wetland condition by evaluating their direct and indirect effects on the macroinvertebrate community and larval tiger salamander abundance. Relationships were quantified among trophic state variables (water-column concentrations of chlorophyll a, nitrogen, phosphorus, total suspended solids, turbidity), fish and salamander abundance, and abundance and taxonomic diversity of plants and invertebrates in 34 continuously-flooded wetlands in north-central Iowa. Results from path analysis supported the hypothesis that fish directly reduced salamander abundance by predation. Results from path analysis and non-metric multidimensional scaling also indicated that fish caused declines in invertebrate numerical densities and taxonomic diversity. However, fish apparently reduced invertebrate abundance and diversity by an indirect mechanism. Specifically, fish increased turbidity which in turn reduced abundance of plants that provide invertebrates with food and habitat. Fish abundance in wetlands increased across a gradient of increasing water depth. Therefore, deeper wetlands were generally in poorer condition than relatively shallow ecosystems. In summary, results provide supporting evidence that fish adversely affect wetland condition by degrading habitat and reducing biodiversity. Mechanisms for fish effects on biological communities appear to vary across taxonomic groups. Pothole wetland condition may be improved by physically disconnecting wetland basins and artificial drainage systems, especially constructed ditches. This action would eliminate migration corridors that allow fish to colonize wetlands, and would reduce surface water inputs that increase wetland depth and fish population persistence.