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

确定群落结构的机制是生态学的一个重要目标，围绕资源(自下而上)和捕食者(自上而下)的重要性存在着相当大的争议。这项拟议的研究试图了解替代机制在构建盐沼生态系统中的食草动物群落时占主导地位的生态环境，并将基于观察性和操纵性实验来做到这一点。特别是，将根据生产率的梯度来评估数据支持四个相互竞争的假设(自下而上控制与自上而下控制、联合控制与环境压力)的程度。析因田间试验将测试是否自下而上对食草动物的影响在低生产率植物上更强，而自上而下对食草动物的影响在高生产率植物上更强。改变寄生蜂的密度将控制自上而下的效应，通过添加氮和活性碳来改变植物品质将控制自下而上的效应。此外，拟议的研究将确定寄生虫影响通过食物链并影响植物的条件，以及自下而上对植物的影响改变天敌捕食草食动物的速度的情况。

0090137Peter StilingIdentifying 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.