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

本建议旨在扩大正在进行的水库和小型水库的工作，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放水域和近岸底栖生物群落中进行测试。东南部的水库是这项工作的重点，与北部的湖泊有很大的不同，因为那里有大量的开放水域杂食性动物沙棘鱼。沙棘鱼既不受鱼类捕食者的控制（由于令人印象深刻的繁殖力，加上对捕食者的脆弱窗口很窄），也不受浮游动物猎物的控制（在仲夏浮游动物崩溃之后，沙棘鱼转向碎屑和浮游植物），沙棘鱼通过“中间”过程调节群落组成，而不是由自上而下或自下而上的力量调节。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，以评估沙棘鱼是否可以控制浮游动物的数量，从而招募蓝鳃鱼（通过对浮游动物的开发竞争）和大口黑鲈（通过减少蓝鳃鱼的猎物）。在过去5年中收集的初步证据有力地支持了这样一种观点，即沙棘鱼可能会很好地驱动俄亥俄州水库的群落组成，因此作为一种“关键”物种，可能会以“中间”的方式运作。本研究的实验方法将通过评估其在由弱生物联系组成的水库食物网中的概念强度来评估级联假说的普遍性。

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.