The Relative Importance of Top-down and Bottom-up Forces along a Plant Productivity/quality Gradient in a Florida Salt Marsh: The Utility of the HSS, Trophodynamics, GGA, & MS Mode

University Of South Florida, Tampa FL

Investigators

Abstract

0090137 Peter Stiling Identifying the mechanisms that structure communities is an important goal of ecology, and considerable controversy surrounds the importance of resources (bottom-up) versus predators (top-down). The proposed research seeks to understand the ecological contexts in which alternative mechanisms predominate in structuring herbivore communities in salt marsh ecosystems, and will do so based on both observational and manipulative experiments. In particular, the extent to which data support four competing hypotheses (bottom-up control vs. top-down control vs. joint control vs. environmental stress) will be evaluated with respect to a gradient in productivity. Factorial field experiments will test if bottom-up effects on herbivores are stronger on low productivity plants whereas top-down effects on herbivores are stronger on high productivity plants. Modifying densities of parasitoids will control top-down effects and modifying plant quality through additions of nitrogen and labile carbon will control bottom-up effects. In addition, the proposed research will ascertain the conditions under which the effects of parasites cascade through the food web and affect plants, and the circumstances in which bottom-up effects on plants alter the rate of predation on herbivores by natural enemies.