LTER: Experimental Isolation of Direct and Indirect Mechanisms in the Trophic Cascade from Fish to Phytoplankton

捕食者会对生态群落产生强烈的影响， 但因果关系往往很难推断， 捕食者之间的直接和间接的物种相互作用， 猎物 最广泛证明的捕食者效应之一是 湖泊生态系统中的“营养级联”。 食浮游鱼罐头 减少了浮游动物的数量和大小，这导致了 浮游植物数量的增加。 这种级联通常 由几个直接和间接的物种相互作用组成， 虽然特定机制在引起 浮游植物的反应尚不清楚。可能机制 包括：1）减少浮游动物摄食率，2）增加 浮游动物释放营养物质，以及3）释放 鱼的营养。 初步实验和计算 表明后一种机制可能比 以前相信。 这项研究提出， 使用一系列嵌套的、分层的 实验将在湖泊中进行，这些湖泊是整个 湖泊捕食者的操控 通过补充整个湖泊 扰动与机械实验，更清晰 对水生食物网的理解将会出现。 由此产生的信息将有助于湖沼学理论， 将直接适用于湖有用的知识库 管理

Predators can have strong impacts on ecological communities, but causality is often difficult to infer because of the myriad direct and indirect species interactions between predators and prey. One of the most widely demonstrated predator effects is the "trophic cascade" in lake ecosystems. Planktivorous fish can reduce the abundance and size of zooplankton, and this results in an increase in phytoplankton abundance. This cascade usually consists of several direct and indirect species interactions, although the importance of specific mechanisms in causing the phytoplankton response is not clear. Possible mechanisms include: 1) reduction of zooplankton grazing rates, 2) increase in release of nutrients by zooplankton, and 3) release of nutrients by fish. Preliminary experiments and calculations suggest that the latter mechanism may be more important than previously believed. This research proposes to experimentally address these mechanisms using a series of nested, hierarchical experiments to be conducted in lakes which are sites of whole- lake predator manipulations. By complementing whole-lake perturbations with mechanistic experiments, a clearer understanding of aquatic food webs will emerge. Resultant information will contribute to limnological theory and will be directly applicable to the knowledge base useful in lake management.