Vegetation Dynamics of Isolated Forest Fragments

特堡9707281 最近的一些研究记录了孤立森林片段中植物物种的急剧损失，但物种损失的机制在很大程度上仍然未知。 研究人员将研究委内瑞拉玻利瓦尔州4,300平方公里的水电蓄水池Lago Guri中10年历史的陆桥岛屿树木群落的持续组成变化。 Lago Guri群岛的面积从1公顷到650公顷不等，被热带干旱森林覆盖。 初步工作表明，小型（1公顷）和中型（10-15公顷）Lago Guri岛屿的动物群落从功能的角度来看非常不平衡：它们缺乏脊椎动物捕食者、种子传播者、大型种子捕食者和授粉者，而小型种子捕食者（啮齿动物）和树栖食叶动物的密度异常高。 拟议的研究将测试整体假设，即不平衡的动物群落正在产生力量，导致Lago Guri岛屿树木群落的转变，因为现有的树冠被陆桥岛屿隔离后建立的树木所取代。 更好地理解的机制，驱动栖息地碎片的保护将有助于管理和破碎化景观的保护规划。 研究人员的结果表明，森林生态系统中缺乏顶级捕食者导致猎物种群的失控增长，特别是食草动物，这严重改变了树木的招聘模式。 受食草动物影响的森林注定会在组成上发生无情的变化，从而导致植物和动物多样性的丧失。

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.