Professor University of Washington Seattle, Washington, United States
Abstract: Lakes support diverse species communities and provide important economic, recreational, and cultural ecosystem services. Lakeshore development, including built infrastructure and landscaping activities, can reduce habitat diversity, macrophytes, and woody debris in littoral (nearshore) environments. These changes alter communities of aquatic macroinvertebrates and prey fish upon which top fish predators depend and may even decouple energy pathways between littoral and pelagic (open water) zones in lakes. Despite the widespread ways in which human activities have disturbed lake shorelines, the food web consequences of these impacts remain unclear. Our study investigated the effects of lakeshore development on food web network structure in lakes throughout the Puget Sound Lowlands. Food web network analysis provides a powerful framework to quantify the effects of perturbations on species interactions and community dynamics. Specifically, we determined lake-specific food web network structure, examined changes in structure across a lakeshore development gradient, and analyzed drivers of these changes.
We conducted standardized littoral and riparian habitat surveys in 12 lakes across a lakeshore development gradient (forested to urbanized). To quantify food web networks, we applied the analytical framework, EcoDiet, which combines diet information from three different data sources – existing literature data, stable isotope analysis (SIA), and stomach content analysis (SCA) – into a single hierarchical Bayesian model. We collected fish, macroinvertebrates, and aquatic and terrestrial plants to conduct SIA of carbon and nitrogen, and identified the stomach contents for fish. We then combined these data using EcoDiet to generate quantitative food web networks. We observed changes in overall network structure, across several key network metrics, as lakeshore development increased. Results suggest that food web connectivity weakens across a development gradient in response to anthropogenic perturbations. As macrophyte cover declined we saw shifts in food web structure due to changes in fish foraging preferences. Additionally, SIA indicated shifting use of littoral and pelagic resources by fish across the development gradient. In this study we use quantitative network analyses to unravel the complex web of species interactions in lakes, which could be a stepping-stone towards building predictive models to anticipate consequences of such disturbances.
