Murray State Theses and Dissertations
Anthropogenic activities have led to degradation in streams throughout much of Western North America. In particular, cattle grazing has led to a loss of riparian vegetation resulting in higher water temperatures and an increase in nutrient runoff. The effects of degradation on food quality and quantity for aquatic consumers could have large implications for stream communities. Since omnivores feed at multiple trophic levels, they may be resilient to altered food webs, which may allow them to stabilize communities in degraded environments where resources have been reduced. To test the hypothesis that omnivores positively impact community stability in degraded conditions, I established artificial mesocosms with varying levels of two disturbance factors: shade (greater shade simulating an intact riparian zone) and nutrients (increased nutrients representing agricultural fertilizer inputs), and the presence or absence of the omnivorous speckled dace (Rhynichtyus osculus), an important consumer in western US streams. Nutrient and shade treatments dictated bottom-up effects on all tanks. Algal biomass increased across all treatments with the greatest increase occurring in tanks with additions of nutrients. Treatments with fish had a higher benthic macroinvertebrate abundance driven by the presence of midge larvae (Chironomidae), however, these same treatments had the lowest abundance of mayflies (Baetidae). Stable isotope analysis confirmed that Speckled Dace were likely switching prey and utilizing the most abundant prey resource. Fish stable istotope δ15N values were higher and had a wider breadth in tanks with higher nutrients. Non-metric multidimensional scaling (NMDS) showed that the communities within degraded tanks with fish grouped with control tanks without fish during the middle of the experiment, indicating that Speckled Dace presence increased the resilience of degraded treatment communities. However, there were no significant differences between communities among any tanks at week 8, indicating a high level of recovery among all communities. In sum, this study suggests that omnivores can play a role in the resilience of degraded aquatic communities, although further research is needed to better understand how this role varies over time and with different types and magnitudes of degradation.
Year manuscript completed
Year degree awarded
Ecology, freshwater science, fisheries
Howard H Whiteman
Michael B Flinn
Christopher J Mecklin
Oliver M Beckers
Moore, Hannah Marie, "Bottom-up effects of degradation outweighs stabilizing potential of omnivores" (2022). Murray State Theses and Dissertations. 261.