Maintenance of Tropical Tree Diversity by Herbivores and Pathogens: A Test of the Janzen-Connell Hypothesis

[04:20031 . Coley]热带森林最显著的特征之一是它们的多样性。对于热带森林树木多样性的维持，最被广泛引用的解释是Janzen-Connell假说，该假说认为，种子捕食者、食草动物和病原体通过优先攻击接近同种成树的种子或幼树来维持多样性。这种攻击率的差异导致了在成年附近较高的幼崽死亡率，并增加了成功的同种新兵之间的距离。因此，树木的天敌被提出来阻止竞争优势，这使得更大的树种多样性得以持续。尽管简森-康奈尔假说在理论上很重要，但很少有研究寻找接近成年的种子或幼苗死亡率较高的预测模式。在了解以成虫为中心的天敌预测机制方面，人们的关注就更少了。本研究将通过以下问题批判性地评估这一假设：1)损害是否取决于与成年同种虫的距离，2)损害是否对生长和生存产生负面影响，以及3)造成大部分损害的食草动物和病原体是否以成人为中心的宿主专家。了解控制热带森林多样性的机制可以应用于热带雨林和人工林的管理。为了不失去管理的森林保护区的多样性，政策应该考虑到詹森-康奈尔效应。例如，鼓励通过种植或选择性采伐来补充，应考虑到与最近同种植物的距离。单一栽培，例如通常在种植园中发现的，往往具有极高的害虫损害水平。初步研究表明，限制损害的一种方法是混合种植，同一物种的任何两个个体之间至少有50米的间距。

9420031 Coley One of the most striking features of tropical forests is their great diversity. The most widely cited explanation for the maintenance of tropical forest tree diversity is the Janzen-Connell hypothesis, which suggests that seed predators, herbivores and pathogens maintain diversity by preferentially attacking seeds or young trees that are close to conspecific adults. This difference in the rate of attack results in higher juvenile mortality near adults and increases the distance between successful conspecific recruits. Thus, the natural enemies of trees are proposed to prevent competitive dominance, which allows a greater diversity of tree species to persist. Despite the theoretical importance of the Janzen-Connell hypothesis, few studies have looked for the predicted pattern of higher seed or seedling mortality near adults. Even less attention has been directed at understanding the predicted mechanism of natural enemies centered on the adults. This study will critically evaluate this hypothesis by asking: 1) whether damage depends on distance from adult conspecifics, 2) whether damage negatively impacts growth and survival, and 3) whether the herbivore and pathogens responsible for the majority of damage are host specialists centered on adults. Understanding the mechanisms which control diversity of tropical forests has applications to management of rain forests as well as cultivated plantations. In order not to lose diversity in managed forest reserves, policies should take into account the Janzen-Connell effects. For example, encouraging recruitment through plantings or selective cutting should consider distance to nearest conspecifics. Monocultures, such as are typically found in plantations, tend to have extremely high levels of damage from insect pests. Preliminary work suggests that one method for limiting damage would be to have mixed planting, with a minimum of 50m between any two individuals of the same species.