| The introduction and establishment of invasive species is one of the major causes of degradation of freshwater ecosystems. I conducted four separate studies addressing exotic species in two geographic areas, the Laja River in Central Mexico, and temperate lakes in the Great Lakes region. Interactions of exotics with native species were investigated from the perspectives of populations, communities, food web interactions and their expansion across the landscape.; I studied how rainbow smelt (Osmerus mordax) invasion can affect walleye (Sander vitreus) populations by reducing the recruitment of young-of-the-year fishes to the adult population in invaded lakes in Wisconsin. The potential of individual lakes for smelt colonization was also investigated, resulting in the identification of 188 lakes where management and invasion prevention efforts should be prioritized.; Through a study of the long term changes of the fish assemblage of the Laja River, I identified changes in the fish community resulting from human impacts. Significant declines in the number of benthivore, carnivore, and sensitive species, and increases in the number of exotic and tolerant species have occurred since the 1960's, resulting in a present-day exotic fish-dominated community, where sensitive species are scarce.; A stable isotope-based food web analysis of the fish communities in the Laja revealed how reservoirs alter the basal resources that fish communities depend on, and how invasive species overlap with natives in terms of resource use. These observations have important implications for understanding how fish communities in other rivers in central Mexico could be affected by exotics and reservoirs.; From a landscape perspective, using morphological, physical-chemical and biological information from Maine lakes where rainbow smelt are native, I developed a model to predict which individual lakes in the Great Lakes region would be suitable for smelt invasion. The model successfully predicted smelt presence/absence in Maine and was used to make broad scale predictions of smelt distribution for over 8000 lakes in Ontario and Wisconsin. The analysis identified 4447 and 553 lakes in Ontario and Wisconsin respectively, suitable for smelt invasion where preventive steps should be taken against the impact of this invasive species. |
