Olden, Julian DJameson, Emily2024-10-162024-10-162024-10-162024Jameson_washington_0250O_27413.pdfhttps://hdl.handle.net/1773/52521Thesis (Master's)--University of Washington, 2024Anthropogenic modification of lake shorelines can eliminate or sharply reduce the elements of shorelines that provide structural diversity in littoral habitats, such as macrophyte and woody debris densities. These changes have been linked to alterations in species abundances, diet patterns, and nearshore food web structure at altered and unaltered shoreline locations within a lake. Few studies, however, have quantitatively examined the association between lakeshore development and food web network structure across lakes with varying levels of lakeshore development. Considering the lake-specific food web networks across multiple lakes could reveal differences in interactions and structural patterns not captured in within-lake studies. In this study, I quantified community structure and species’ positions in food webs across lakes with varying degrees of lakeshore residential development to identify associations between the two. I selected 12 lakes in the Puget Sound lowlands, and for each conducted standardized habitat surveys by measuring littoral and riparian habitat complexity, and recording dock density along the lakeshore, pelagic chlorophyll-a concentration, and lake area. To estimate feeding habits of fish, I employed both stable isotope analysis and stomach content analysis. Additionally, I used stable isotope analyses to examine diet patterns in aquatic macroinvertebrates. I integrated data from both techniques with preexisting information from the literature within a relatively new analytical framework, EcoDiet, to estimate the proportion of each prey type in the diets of fish and predacious macroinvertebrates within the food web. To quantify species’ roles within the food web I calculated diet breadth, diet evenness, and betweenness centrality (relative importance in connecting disparate parts of the food web, hereafter centrality) for each predatory species. I then quantified food web metrics from the estimated lake-specific food webs using network analyses to calculate the connnectance, mean link strength, and mean degree within each food web. Finally, I assessed the correlations among these network metrics and the measured environmental variables using redundancy analysis (RDA), principal component analysis (PCA), and bivariate regressions. My results suggest that while pelagic chlorophyll-a concentration and the presence of largemouth bass were associated with changes in diet patterns within the food web, lakeshore development had little effect on overall food web connectance. Yellow perch and pumpkinseed exhibited a positive correlation between centrality and both pelagic chlorophyll-a concentrations and the presence of largemouth bass. Thus, both yellow perch and pumpkinseed were more important in connecting basal resources to upper trophic levels when primary production was high and largemouth bass were present in the lakes. Fish species exhibited different associations with lakeshore development and diet breadth and diet evenness. For instance, yellow perch (Perca flavescens) diet breadth and diet evenness were positively correlated with lakeshore residential development, whereas largemouth bass (Micropterus salmoides) diet breadth was negatively correlated, and pumpkinseed (Lepomis gibbosus) displayed little change in diet breadth or diet evenness. The net effect of these species-specific responses was a weak and positive association between food web connectance and both dock density and lake area. Because none of the lakes in this study were undisturbed (the least developed lake having residential development on 25% of its lakeshore), it is possible that changes to food web connectance occur at lower levels of lakeshore residential development than was measured in this study. High network connectance can stabilize food webs, therefore, the weak correlation between connectance and lakeshore residential development suggests that food web stability may be similar among the disturbance levels measured in this study. Future research could directly examine the relationship between lakeshore development, food web network structure, and stability across a wider range of lakeshore development.application/pdfen-USnoneAquatic sciencesFisheriesThesis