Do Differential Responses to Desiccation, Herbivory and Light Determine the Habitat Specializations of Rainforest Trees Along a Rainfall Gradient?

生态系统为人类提供了许多服务。纵观历史，森林满足了人类的许多需求。森林为城市地区提供水源。来自温带和热带森林的木材在美国和世界经济中也扮演着至关重要的角色。此外，森林还蕴藏着惊人的生物多样性。这些观察结果尤其适用于热带森林，尽管它们显然很重要，但转换的速度是不可持续的。虽然人们普遍认识到热带森林表现出高度的多样性，但也确实，相距仅几公里的地点在树木(和动物)物种上存在很大差异。为了保护和管理这种森林，我们必须了解决定树木分布和丰富度的因素。虽然人们很早就认识到热带树木的分布模式非常复杂，但决定其分布的因素还不是很清楚。许多人认为降雨和干旱是重要因素，但缺乏科学证据。在低地热带森林，树木分布的主要决定因素可能是干旱(降雨)、昏暗林下的光照可获得性和植物敌人(食草动物)。在这个项目中，研究人员将通过实验评估这三个因素在确定巴拿马地峡地区树木分布方面的相对重要性。巴拿马提供了一个很好的实验室，因为潮湿的加勒比海一侧的树种在干燥的太平洋一侧基本上不存在(反之亦然)，导致这种模式的过程尚不清楚。量化降雨、光照和食草动物对树木分布的影响在世界各地的热带森林保护和管理中有着广泛的应用。

Ecosystems provide many services to humankind. Throughout history, forests have fulfilled many human needs. Forests provide water stores for urban areas. Wood, from temperate and tropical forests, also plays a vital role in the US and world economies. Moreover, forests also harbor astonishing biodiversity. These observations apply especially to tropical forests that, despite their evident importance, are converted at an unsustainable rate. While it is widely appreciated that tropical forests display high diversity, it also is true that sites separated by only kilometers differ considerably in tree (and animal) species. In order to protect and manage such forests, we must understand the factors that determine the distributions and abundances of trees. Although the very complex patterns of distribution of tropical trees have long been recognized, the factors that determine distribution are not understood. Many argue that rainfall and drought are important factors, but scientific demonstrations are lacking. In lowland tropical forests, the principal determinants of tree distributions probably are drought (rainfall), light availability in the dim understory and plant enemies (herbivores). In this project, investigators will evaluate experimentally the relative importance of these three factors in determining tree distributions across the Isthmus of Panama. Panama provides an excellent laboratory since the tree species on the wet, Caribbean side are largely absent on the dry, Pacific side (and vice versa) and the processes that cause this pattern are unknown. Quantifying the impact of rainfall, light and herbivores on tree distributions has broad applications for the protection and management of tropical forests worldwide.