Date Approved

8-2012

Graduate Degree Type

Thesis

Degree Name

Biology (M.S.)

Degree Program

Biology

Abstract

Mesohabitats are visually distinct areas within a stream that provide habitat heterogeneity and increase invertebrate diversity. As such, mesohabitats represent an important spatial scale that underpins the emergent properties, ecology, and ecosystem structure and function of a stream. Within a Western Michigan stream, woody debris, macrophyte beds, and organic matter pools, were examined to determine if visual distinction also relates to a significant difference in abiotic and biotic parameters. Habitats were sampled from July, 2010 – June, 2011 for chemical-physical characteristics including velocity, temperature, pH, conductivity, turbidity and organic matter. Biotic sampling occurred during the same time span and included benthic chlorophyll-a and invertebrates. Principal components analysis (PCA) revealed that conductivity, temperature, and pH effect mesohabitats in similar ways and that mesohabitat types are characterized most strongly by water velocity and particulate organic matter (POM). Total POM was highest in pools and macrophyte beds with mean amounts of 5,800 (SE ± 530) g·m-2 and 1,935 (SE ± 346) g·m-2 respectively. Chlorophyll-a concentrations were not significantly different among mesohabitats. Invertebrate sampling revealed greater richness and diversity within macrophytes beds and woody debris compared to pools. Macrophytes had the highest mean invertebrate densities (18,3881 ind·m-2 SE± 41,741) and mass (14.54 g·m-2 SE±3.05). Chironomidae densities dominated all habitat types with one macrophyte bed sample surpassing 600,000 ind·m-2. When not including Chironomidae numbers, similarity of percent (SIMPER) results show Gammarus as the vi most dominant taxa separating habitats, and Baetis and Simulidae as the second and third most dominant taxa. Invertebrate assemblages significantly separated in multidimensional space with assemblages in woody debris correlating most strongly with higher water velocities, organic matter pools correlating most strongly with total POM, and macrophytes falling in-between the two. Based on these results, I propose three conclusions for Michigan sand-dominated streams: 1) that riparian trees, through the addition of woody debris, and macrophytes beds are acting as ecological engineers through the retention of POM, changes in stream velocity, and likely changes in stream morphology, 2) that mesohabitats are distinct in both abiotic and biotic factors and may prove beneficial as a patch scale for management implications, and 3) that mesohabitat heterogeneity, especially macrophyte beds and woody debris, is important for invertebrate abundance and diversity within sand-dominated streams.

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