Enemies Maintain Hyperdiverse Tropical Forests
Enemies Maintain Hyperdiverse Tropical Forests
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DOI：
10.1086/664183
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发表时间：
2012-03-01
影响因子：
2.9
通讯作者：
Terborgh, John
中科院分区：
文献类型：
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作者：
Terborgh, John
了解热带森林树木的多样性一直是生态学家面临的一个重大挑战。在缺乏补偿机制的情况下，两种强大的力量，漂移和竞争，预计将迅速侵蚀多样性，特别是在包含数十个或数百个稀有物种的社区。在这里，我回顾了四个补偿机制的证据，已被归入术语“密度依赖”或“负密度依赖”：（1）种内和（2）种间竞争和行动（3）密度响应和（4）距离响应的生物因子，如Janzen和Connell假设。为了实现本体论的整合，我研究证据的基础上，采用种子，幼苗和树苗。现有的证据压倒性地指出，主机的通才和主机限制的生物剂的行动，造成大多数种子和幼苗死亡率，这意味着物种多样性是通过自上而下的强迫保持。大多数寄主通性种子捕食者和食草动物的总体效果是均匀分布幸存的繁殖体。空间限制招聘的结果似乎主要是，如果不是唯一的，从主机限制代理，主要是microarthropods和真菌，攻击主机的距离依赖的方式Janzen和康奈尔提出的行动。接近繁殖同种的繁殖体几乎完全失败，这确保了通过少量的种子分散而成功繁殖。分散的种子和由此产生的幼苗的密度是如此之低，以至于通常排除了密度依赖的作用，至少在早期个体发育阶段是如此。我的结论是，Janzen和康奈尔基本上是正确的，多样性的维护结果自上而下的强迫作用在空间上不均匀的方式。
Understanding tropical forest tree diversity has been a major challenge to ecologists. In the absence of compensatory mechanisms, two powerful forces, drift and competition, are expected to erode diversity quickly, especially in communities containing scores or hundreds of rare species. Here, I review evidence bearing on four compensatory mechanisms that have been subsumed under the terms "density dependence" or "negative density dependence": (1) intra-and (2) interspecific competition and the action of (3) density-responsive and (4) distance-responsive biotic agents, as postulated by Janzen and Connell. To achieve ontological integration, I examine evidence based on studies employing seeds, seedlings, and saplings. Available evidence points overwhelmingly to the action of both host-generalist and host-restricted biotic agents as causing most seed and seedling mortality, implying that species diversity is maintained via top-down forcing. The overall effect of most host-generalist seed predators and herbivores is to even out the distribution of surviving propagules. Spatially restricted recruitment appears to result mainly, if not exclusively, from the actions of host-restricted agents, principally microarthropods and fungi, that attack hosts in a distance-dependent fashion as Janzen and Connell proposed. Near total failure of propagules close to reproductive conspecifics ensures that successful reproduction occurs through a scant rain of dispersed seeds. Densities of dispersed seeds and seedlings arising from them are so low as to generally preclude the operation of density dependence, at least during early ontogenetic stages. I conclude that Janzen and Connell were essentially correct and that diversity maintenance results from top-down forcing acting in a spatially nonuniform fashion.