Top-Level Carnivores and Ecosystem Effects: Questions and Approaches
Top-Level Carnivores and Ecosystem Effects: Questions and Approaches
复制标题
顶级食肉动物和生态系统影响：问题和方法
DOI：
--
复制
发表时间：
1995
期刊：
影响因子：
--
通讯作者：
J. Estes
中科院分区：
文献类型：
--
作者：
J. Estes
顶级食肉动物包括各种各样的分类群，并出现在大多数自然生态系统中。本章考虑了三个主要问题：顶级食肉动物的生态和进化影响是什么，它们有多普遍，它们在什么条件下发生？要回答这些问题，首先必须确定食物网是否处于自上而下的控制之下，最终确定存在自上而下控制的物种、系统和环境。对于受自上而下力量影响的系统，食肉动物对自养生物的级联效应预计会随着营养复杂性的顺序而变化。在这个概念框架下，探讨了三个更具体的问题。首先，顶级食肉动物的直接和间接影响有多普遍？第二，食肉动物的直接影响对营养的影响有多大？对于那些(1)顶级食肉动物占据奇数营养级和(2)食物网紧密相连的系统，预计会产生广泛的影响。(3)营养级联对食物网中较低层物种的进化后果是什么？这些问题最好通过操纵或自然实验来回答，在这些实验中，食肉动物的存在或不存在在空间或时间上是不同的。对于许多物种和系统来说，自然实验被认为是解决这些问题的唯一实际手段，特别是那些关键参与者庞大且高度移动的物种和系统，或者那些对捕食者的操纵具有法律、政治或社会后果的物种和系统。
Top-level carnivores comprise a diverse array of taxa and occur in most natural ecosystems. This chapter considers three main questions: What are the ecological and evolutionary effects of top-level carnivores, how general are they, and under what conditions do they occur? To answer these questions one first must determine whether a food web is under top-down control, and ultimately, the species, systems, and circumstances for which top-down control exists. For systems affected by top-down forces, the cascading effect of carnivory on autotrophs is expected to vary with the order of trophic complexity. Given this conceptual framework, three more specific questions are explored. First, how general are the direct and indirect effects of top-level carnivores? Second, what is the breadth of trophic influence from the direct impact of carnivory? Broadly ranging effects are expected for systems in which (1) top-level carnivores occupy odd-numbered trophic levels and (2) the food web is strongly linked. (3) what are the evolutionary consequences of trophic cascades on species lower in the food web? These questions can best be answered via manipulative or natural experiments in which the presence or absence of carnivores varies in space or time. Natural experiments are advocated as the only practical means of addressing these questions for many species and systems, in particular those in which the key players are large and highly mobile, or those in which the manipulation of predators has legal, political, or social ramifications.