Collaborative Research: The structure of arthropod food webs: consequences of nutrient-loading scenarios for productivity, trophic composition and food-chain length.

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The effects of contrasting nutrient-input regimes on food-web structure in natural habitats remain poorly understood, despite the increasing fraction of landscapes experiencing nutrient runoff from agriculture and development. The intellectual merit of this project lies in its expansion of food-web theory to include complex nutrient dynamics that affect not only plant productivity but also interactions among consumers. The investigators will examine the effects of nutrient subsidies on food web dynamics in coastal salt marshes dominated by Spartina cordgrasses using a blend of manipulative field experiments and surveys of marshes that vary in nitrogen inputs. The long-term goal is to understand the relationship between primary productivity and food chain length and trophic composition in a system characterized by extensive omnivory and intra-guild predation.The broader impacts of this study extend beyond the testing and development ofecological theory. Because coastal wetlands play a critical role in the ecology and geology of wave-protected shorelines and are the nursery grounds for commercial fish and shellfish, their conservation is of major concern. Urban development and agriculture are jeopardizing these wetlands; nitrogen runoff increases plant growth, which subsequently has profound effects on all other salt marsh inhabitants. The resilience of salt marshes to repeated bouts of nitrogen addition is poorly understood. The proposed research will provide diverse educational opportunities for a postdoctoral researcher, graduate and undergraduate students. The investigators plan to participate in the District of Columbia Summer Youth Employment Program to hire two high school students from the metropolitan Washington, DC area each summer. This program matches residents of the District of Columbia with employers so that the students may gain exposure to new career opportunities.