| Aquatic ecosystems are very vulnerable to the effects of invasive species. Nonnative species have contributed to the extinction of many North American freshwater fishes. This dissertation research explores several aspects of the biology of an invading species, Catostomus commersoni, and a native, declining congener, C. plebeius, in an attempt to understand how C. commersoni displaces C. plebeius .; In chapters 1 and 2, the geographic distribution of genetic diversity of C. commersoni and C. plebeius, respectively, were examined to understand how dispersal affects population structuring within the species' ranges in New Mexico. The introduction of lineages into both the native and non-native range of the C. commersoni has lead to a complex relationship between geography and phylogenetic relationships at the edge of this species' range, with presence of two distinct lineages in the introduced population in the upper Rio Grande. For C. plebeius , significant geographic structuring was detected between the Mimbres/Sapillo populations, Palomas Creek and tributaries to the upper Rio Grande at both mitochondrial and nuclear loci. Results from the upper Rio Grande populations were consistent with low gene flow and incomplete lineage sorting.; In chapter 3, two nuclear microsatellite markers and one mitochondrial DNA marker were used to study hybridization between the two species. Of 436 larvae, young-of-year, and adults from the upper Rio Grande basin, no F1 or backcross hybrids were detected. This result indicated that widespread hybridization and/or introgression with C. commersoni is not responsible for the decline of C. plebeius.; Finally, in the fourth chapter, life history traits of these two species were compared. While there was little difference in size and growth of the two species in the first year of life, C. commersoni attained a longer lifespan, larger adult body size, and an order of magnitude greater fecundity than did C. plebeius. However, life table analysis suggested that by maturing one year earlier and experiencing lower mortality rates, C. plebeius had similar lifetime reproductive output as did C. commersoni. C. commersoni's high fecundity lead to its numerical dominance in the first year of life. |
