From Second Creek to New Pangea: A Multi-Scale Analysis of Patterns and Trends in Aquatic Biodiversity

The Earth’s freshwater ecosystems are undergoing a period of dramatic change. The simultaneous expansion and contraction of aquatic species’ ranges is leaving an indelible mark on the evolutionary histories of the world’s freshwater species. This dissertation represents a compilation of research efforts that quantify, explain, and propose policy recommendations concerning current trends in aquatic biodiversity. Part II provides an appraisal of the status of the world’s freshwater fishes that asks two primary questions—are all taxonomic groups equally susceptible to extinction, and can we identify a unifying suite of extinction risk factors? Although I concluded, that extinction risk is not randomly distributed among freshwater fish families, the identification of a unifying set of extinction predictors remains elusive. In Part III, focusing on the U.S., a species list was compiled for each of the lower 48 states to represent their historic and future freshwater fish faunas. Species richness was calculated for each state, and the degree of change in faunal similarity was estimated between neighboring states. Comparisons indicated that states are likely to become more distinct from their neighbors in the future. In Part IV, I evaluate aquatic diversity trends along a natural gradient within the state of Tennessee. Changes in species richness and faunal similarity occurring between historic and future faunas were calculated between ecoregions. Species richness was found to decrease statewide. Similarity increased for virtually all ecoregion-taxonomic combinations indicating that Tennessee is losing its historic biological distinctiveness. Part V represents a study of biophysical homogenization at a fine spatial scale. I compared the frequency of debris dams in a forested reference stream to a stream in a heavily urbanized watershed. I found that debris dams occurred in greater frequency within the forested reference stream compared to the urban stream. A follow-up analysis determined that although there was a significantly greater amount of riparian canopy litter within the urban stream corridor, the quality and timing of litter inputs prevented debris dam genesis and retention. It is believed that the scouring flows that typically accompany highly impervious urban watersheds contributed to decreased frequency of debris dams in the urban stream.