Collaborative Research: Intermediate Regulations of Aquatic Ecosystems: Pursuing the Generality of the Trophic Cascade Hypothesis

这项建议旨在扩展水库和小型蓄水池正在进行的工作，寻求对营养级联假说的一般性进行评估。这一假设目前正在北温带开阔水域和近岸海底群落中得到验证。东南部水库是这项工作的重点，与北部湖泊的显著不同之处在于，开阔水域的杂食性动物--蜥蜴--大量出现。既不受鱼类捕食者(由于令人印象深刻的繁殖力加上对捕食者的脆弱窗口)也不受它们的浮游动物猎物(在仲夏浮游动物崩溃后，沙鱼转向碎屑和浮游植物)的控制，蜥蜴通过“中间向外”的过程来调节群落组成，而不是受到自上而下或自下而上的力量的调节。这些研究人员设计了一系列空间尺度(1立方米到100公顷)的实验，以评估砂鱼是否可以控制浮游动物的数量，从而补充蓝鳍金枪鱼(通过对浮游动物的剥削竞争)和大口黑鱼(通过减少它们的蓝鳍金枪鱼猎物)。过去5年收集的初步证据有力地支持了这样一种观点，即沙鱼很可能推动俄亥俄州水库的群落组成，从而成为一种很可能以“中间向外”方式运行的“关键”物种。这项研究的实验方法将通过评估由弱生物联系组成的水库食物网的概念强度来评估级联假说的一般性。

This proposal seeks to extend ongoing work in reservoirs and small impoundments, pursuing an evaluation of the generality of the trophic cascade hypothesis. This hypothesis is currently being tested in north temperate open-water and inshore, benthic communities. Southeastern reservoirs, the focus of this work, differ dramatically from northern lakes in that an open-water omnivore, gizzard shad, occurs in abundance. Neither controlled by fish predators (owing to impressive fecundity coupled with a narrow window of vulnerability to predators) nor by their zooplankton prey (following the mid-summer zooplankton crash, shad switch to detritus and phytoplankton), gizzard shad regulate community composition via "middle-out" processes, rather than being regulated by top-down or bottom-up forces. These investigators have designed a series of experiments across a range of spatial scales (1 m3 to 100 hectares) to evaluate whether gizzard shad can control zooplankton populations and hence recruitment of bluegill (via exploitative competition for zooplankton) and largemouth bass (by reducing their bluegill prey). Preliminary evidence gathered during the past 5 years strongly supports the perspective that gizzard shad may well drive community composition in Ohio reservoirs, thus serving as a "critical" species that may well operate in a "middle-out" fashion. The experimental approach of this study will evaluate the generality of the cascade hypothesis by assessing its conceptual strength in reservoir food webs comprised of weak biotic linkages.