Term of Award

Summer 2018

Degree Name

Master of Science in Biology (M.S.)

Document Type and Release Option

Thesis (open access)

Copyright Statement / License for Reuse

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.

Department

Department of Biology

Committee Chair

James Roberts

Committee Member 1

Stephen Vives

Committee Member 2

Christine Hladik

Committee Member 3

Mark Scott

Abstract

Effective management of freshwater fishes requires a mechanistic understanding of the drivers of assemblage composition; in other words, what determines who is where and when. Stream fish assemblages are potentially influenced by environmental factors that act on multiple spatiotemporal scales, but the relative influence of these drivers may vary between geophysically distinct regions. This study sought to determine the patterns and drivers of fish taxonomic and functional assemblage composition in the coastal plain, a region possessing unique hydrologies, faunas, and physiochemical conditions. I addressed this goal using two complementary chapters, both of which utilized environmental and biotic data collected from twenty-six wadeable coastal plain streams in the Altamaha, Ogeechee, and Savannah River basins in Georgia during the summers of 2016 and 2017. In the first chapter, I compared the relative influence of both regional landscape-scale (e.g. land use, ecoregion memberships) and local habitat-scale (e.g. water chemistry, stream morphology) environmental factors on species richness and taxonomic assemblage composition. In the second chapter, I tested the abilities of six longstanding ecological models to predict observed longitudinal changes in habitat and fish assemblages in coastal plain streams. Results from this study indicate that both species richness and taxonomic composition of assemblages were influenced by environmental conditions acting at multiple scales, including drainage area, channel sinuosity, water chemistry, and substrate. In addition, coastal plain fish assemblages sorted spatially into two distinctive assemblage types (i.e. “fluvial” and “nonfluvial”) that were characterized by differences in key environmental variables, most of them local in scale. Taxonomic assemblage composition remained stable over time, despite significant annual differences in hydrology. As frequently observed elsewhere, I detected increasing species richness in larger, downstream reaches. However, other longitudinal gradients in environmental conditions and species’ traits showed variable influence for stream size, providing substantial support for the River Continuum Concept, modest support for the Habitat Template Concept, and little support for four other models. I posit that this was because of the naturally harsh physiochemical regime and variable hydrology of coastal plain systems which limited the action of longitudinal filtering mechanisms observed in other regions. This study allows for a better understanding of how and why coastal plain stream fish assemblages are structured taxonomically and functionally, and lends insight into how communities may respond to environmental changes.

Research Data and Supplementary Material

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