Factors influencing community structure of riverine organisms. Implications for imperiled species management
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Riverine environments are dynamic with numerous biophysical components influencing community structure of riverine biota. Common theme among my dissertation chapters is the quantification of community structure related to biophysical components of riverine environments in an effort to identify mechanisms underlying community structure (e.g., species richness, species abundances, life history traits). Communities within two Texas river basins (i.e., Red River drainage, Colorado River drainage) include several species identified as imperiled species, either federally or by states. A goal for each chapter was to integrate patterns and processes of community structure with current efforts to list species under the Endangered Species Act or to mediate negative anthropogenic influences on species and communities. Chapter 1 addressed gaps in life history information, current distribution, and habitat associations for the Red River Shiner, an endemic cyprinid in the Red River basin. Information was used to estimate redundancy, resiliency, and representation of the Red River Shiner, following the framework of U.S. Fish and Wildlife Service in species status assessments and eventually listing decisions. Chapter 2 tested three theories related to largescale migrations of prairie stream fishes, using the federal candidate for listing Prairie Chub as a model organism. Chapter 3 was a fish community assessment of the upper Red River of Texas and Oklahoma and quantified historical to contemporary changes in occurrences and abundances of six species of greatest conservation need. Chapter 4 was a mussel community assessment of the Colorado River basin that identified georegion, along with associated substrates, stream gradient, and water quality, as more powerful predicator of community structure than smaller scale mesohabitat characteristics. Fish and mussel communities were not homogenously distributed within a basin, and I successfully quantified the heterogeneity and identify some of the potential mechanisms. However, mechanisms of community structure are still largely elusive and in need of further investigation.