Date of Graduation

12-2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Biology (PhD)

Degree Level

Graduate

Department

Biological Sciences

Advisor/Mentor

Magoulick, Daniel D.

Committee Member

Evans-White, Michelle A.

Second Committee Member

Willson, John D.

Third Committee Member

Cothren, Jackson D.

Keywords

Aquatic Ecology; Community Ecology; Disturbance Ecology; Ecological Models; Meta-Food Webs; Stream Ecology

Abstract

Disturbances occur when an external force modifies a habitat, destroying living space, removing food resources, or altering or destroying habitat structure. In lotic systems, a primary source of disturbance is hydrologic disturbance, including drought and flood. Hydrologic disturbances lead to increased mortality rates and dispersal out of disturbed habitats, causing population sizes to decrease and changes to community structures. More research is needed on how disturbances impact stream species and communities, as disturbances are predicted to become more intense with climate change. This dissertation aims to understand how disturbance influences streams at both the population and community level, through a spatial occupancy model of Smallmouth Bass (Micropterus dolomieu), an analysis of food chain length and fish assemblage composition in flow regimes with different levels of hydrologic disturbance, and a meta-food web model with three multi-patch topologies. The spatial occupancy model was performed using Spatial Stream Network modeling on Smallmouth Bass at the southern extent of their range, the Ozark-Ouachita Interior Highlands. Hydrologic variation was the main driver of Smallmouth Bass occurrence. Smallmouth Bass were most likely to occur in groundwater streams with low levels of hydrologic variation. When modeling just groundwater streams, the only significant relationships were a positive relationship between occurrence and mean summer stream temperature and a negative relationship between occurrence and mean annual stream temperature. As hydrologic variation increased, in runoff and intermittent streams, relationships with environmental variables became more important and spatial autocorrelation explained a greater proportion of the model results. Food chain length was determined using stable isotopes and a redundancy analysis (RDA) was performed to determine if there were differences in fish assemblages between flow regimes. The more hydrologically variable runoff flashy streams had a shorter food chain length than the more stable groundwater flashy streams. This was likely due to differences in fish assemblages between the two flow regimes. The meta-food web model found that all multi-patch network topologies had a greater network robustness than patch robustness and a greater network robustness than single patches. Disturbance caused a decrease in network and patch robustness for all topologies, however dendritic topologies had lower resistance than linear or lattice topologies and decreased more. Dendritic networks also had a higher resilience and patch robustness increased a greater amount after disturbance ended than linear or lattice networks. This dissertation shows how disturbance can impact individual populations and entire communities. Hydrologic disturbance is a driving force in Smallmouth Bass distributions, significantly influences fish assemblage composition and food chain length, and impacts food webs in meta-food webs. The dendritic spatial structure of streams plays an integral role in each of these. As disturbances increase in frequency and intensity, it will be essential to understand how disturbances impact populations and communities and the differences in impacts as a result of spatial structure.

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