Vegetation Dynamics of Isolated Forest Fragments

特尔堡9707281最近的一些研究记录了孤立的森林碎片中植物物种的戏剧性损失，但物种损失的机制在很大程度上仍不清楚。调查人员将检查委内瑞拉玻利瓦州一个4300平方公里的水电站蓄水池拉戈古里有10年历史的陆桥岛屿树木群落的持续组成变化。拉戈古里岛的面积从1公顷到650公顷不等，被热带干燥的森林覆盖。初步工作表明，从功能角度来看，小型(1公顷)和中型(10-15公顷)拉戈古里岛的动物群落非常不平衡：它们缺乏脊椎动物捕食者、种子传播者、大型种子捕食者和传粉者，小型种子捕食者(啮齿类)和树栖叶食动物的密度异常高。这项拟议的研究将检验总体假设，即不平衡的动物群落正在产生力量，将导致拉戈古里群岛的树木群落发生变化，因为现有的树冠被陆桥岛屿孤立后建立的树木取代。更好地了解导致栖息地碎片灭绝的机制将有助于在受管理的和支离破碎的景观中进行保护规划。研究人员的结果表明，森林生态系统中没有顶级捕食者会导致猎物种群的失控增长，特别是草食动物，这进而严重改变了树木招募的模式。受食草动物影响的森林注定会在组成上发生不可阻挡的变化，导致动植物多样性的丧失。

TERBORGH 9707281 A number of recent studies document dramatic losses of plant species in isolated forest fragments, but the mechanisms of species loss remain largely unknown. The investigators will examine ongoing compositional change in the tree communities of 10-year old land-bridge islands in Lago Guri, a 4,300 km2 hydroelectric impoundment in the State of Bolivar, Venezuela. Lago Guri islands range in size from 1 ha to 650 ha and are covered by tropical dry forest. Preliminary work has shown that the animal communities of small (1 ha) and medium (10-15 ha) Lago Guri islands are strikingly imbalanced from a functional standpoint: they are deficient in vertebrate predators, seed dispersers, large seed predators, and pollinators, and contain abnormally high densities of small seed predators (rodents) and arboreal folivores. The proposed research will test the overall hypothesis that imbalanced animal communities are generating forces that will result in transformation of the tree communities of Lago Guri islands as the existing canopy is replaced by trees that established subsequent to isolation of the land-bridge islands. A better understanding of the mechanisms that drive extinctions in habitat fragments will facilitate conservation planning in managed and fragmented landscapes. The investigators' results suggest that the absence of top predators in forest ecosystems leads to runaway growth of prey populations, especially herbivores, which then severely alter the pattern of tree recruitment. Forests affected by herbivores are destined to change inexorably in composition with a resulting loss of diversity of both plants and animals.