NUTRIENT AND STRUCTURAL EFFECTS OF DETRITUS ON FOOD WEB INTERACTIONS IN AN INTERTIDAL MARSH

Abstract

In most systems the majority of plant primary production is not directly consumed by herbivores, but instead dies and enters the system as detritus. This study examines indirect (nutrient) and direct (structural) impacts of detritus on the aboveground community of arthropods associated with the Spartina alterniflora. I manipulated carbon, nitrogen, and detrital resources in a field experiment and measured the response of the aboveground and belowground communities. Herbivore density in the field was limited by carbon supplements that also decreased decomposition rates, and limited plant size as well as predator abundance. Nitrogen addition enhanced herbivore density by increasing decomposition rate, inorganic soil nitrogen pools, and plant quality. In the laboratory, thatch directly affected herbivore fitness by decreasing survivorship and male body size. Overall, results suggest that detritus has the potential to adversely affect aboveground herbivores directly by decreasing fitness and indirectly by reducing plant biomass and enhancing natural enemy abundance.