| Many studies have shown that fish can influence the structure and processes of aquatic ecosystems, but studies with replication at the ecosystem level are rare, as are studies involving wetlands. Some wetlands of the Prairie Pothole Region of North America support fish communities dominated by fathead minnows while others are fishless, providing an opportunity to assess the influence of these fish on wetland ecosystems. Additionally, extensive drainage of prairie wetlands has led to restoration of thousands of basins, but the success of these efforts is poorly known. I assessed the effects of fathead minnows and prior drainage on characteristics of prairie wetlands by studying 20 semipermanent wetlands in Minnesota from 1996–1999. I used a 2 x 2 factorial design to examine the effects of minnows (presence/absence) and drainage (restored/non-drained) on the abundances of aquatic invertebrates, aquatic macrophytes, and amphibians, as well as water-column levels of chlorophyll a, total phosphorus, total nitrogen, and turbidity. Results showed that presence/absence of fathead minnows is an important determinant of many biotic and abiotic characteristics of prairie wetlands. Wetlands with minnows had significantly fewer aquatic insects, large and small-bodied cladocerans, calanoid copepods, ostracods, and larval tiger salamanders, as well as a higher abundance of corixids and higher levels of turbidity and chlorophyll a. In contrast, higher concentrations of phosphorus in restored basins was the only consistent history effect, and no consistent fish x history interactions were detected. Additional research showed that the ecological characteristics of prairie wetlands can change rapidly in response to both minnow colonization and elimination. Thus, temporal variability in minnow presence/absence may be a source of temporal variability in other ecosystem components. Abiotic variables influence prairie wetlands, but this research indicates that these ecosystems may also be strongly influenced by the presence/absence of minnows. Inter-basin and inter-annual variability in minnow presence may be important for maintaining diverse assemblages of species at the landscape level, with fishless basins favoring certain assemblages of organisms and basins with minnows favoring others. From a management perspective, these effects should be considered prior to landscape manipulations that alter the regional proportion of basins supporting fathead minnow populations. |
