Mammals, edge effects, and the loss of tropical forest diversity
Mammals, edge effects, and the loss of tropical forest diversity
复制标题
DOI：
10.1890/03-0575
复制
发表时间：
2005-02-01
期刊：
影响因子：
4.8
通讯作者：
Mejía-Chang, M
中科院分区：
文献类型：
--
作者：
Asquith, NM;Mejía-Chang, M
相对于周围的大陆森林，巴拿马加通湖暴露在风中的森林岛屿上以树种的子集为主。我们探索了这些碎片中的树木多样性如何受到（1）哺乳动物群落的贫困和（2）岛屿形成后非生物条件变化的影响。 90年前。为了测试哺乳动物群落变化的影响，我们评估了五个森林中九种树种的种子和幼苗存活率：没有哺乳动物的小岛屿；小岛屿上有带刺的老鼠，但没有较大的哺乳动物；中型岛屿（中型哺乳动物群落）；巴罗科罗拉多岛（间歇性出现美洲狮和美洲虎）；和大陆森林（完整的哺乳动物群落）。为了测试非生物胁迫的影响，我们选择了暴露于风、防风和内部森林的实验地点。我们预测，哺乳动物群落多样性较低的碎片将具有以下特征：（1）分散和储存的种子较少，（2）种子的长期存活率较低，以及（3）哺乳动物食草幼苗的比率较高。在环境变化导致更多地暴露于旱季风的情况下，我们预测（4）发芽和幼苗建立以及（5）旱季幼苗存活率会较低。此外，我们预计，如果土壤湿度提高，（6）旱季幼苗的存活率会增加，但（7）湿季幼苗的存活率与风暴露无关。在较大的森林中，种子和幼苗的存活率较低，哺乳动物群落组成的差异影响不大。只养老鼠的小岛屿的种子存活率与大森林一样低。消除所有哺乳动物导致种子存活率更高，幼苗存活率也更高。暴露在风中的发芽率和幼苗存活率低于受保护地点，但灌溉对旱季幼苗存活率没有影响。加通湖碎片上的优势物种似乎经过了一系列过滤：种子首先要避免被刺鼠吃掉，度过第一个旱季，然后避免幼苗被老鼠食草。生物和非生物因素决定热带森林中幼苗的存活；这些因素的协同变化可能导致多样性的急剧丧失。
Relative to the surrounding mainland forests, a subset of tree species dominates wind-exposed, forested islands in Gatun Lake, Panama. We explored how tree diversity in these fragments has been affected by (1) impoverishment of the mammal community and (2) changes in abiotic conditions following island formation ca. 90 years ago. To test effects of changes in the mammal community, we assessed seed and seedling survival for nine tree species in five forests: small islands with no mammals; small islands with spiny rats but no larger mammals; medium islands (intermediate mammal community); Barro Colorado Island (intermittently present puma and jaguar); and mainland forests (intact mammal community). To test effects of abiotic stress, we chose experimental sites at wind-exposed, wind-protected, and interior forest sites. We predicted that fragments with less diverse mammal communities would be characterized by (1) fewer seeds dispersed and cached, (2) lower long-term seed survival, and (3) higher rates of seedling herbivory by mammals. Where alteration of the environment has caused greater exposure to dry-season winds, we predicted that (4) germination and seedling establishment and (5) dry-season seedling survival would be low. Further, we expected that (6) dry-season seedling survival would increase if soil moisture levels were raised, but that (7) wet-season seedling survival is independent of wind exposure.In the larger forests, seed and seedling survival were low, and differences in mammal community composition had little effect. Small islands that supported only rats had the same low seed survival as larger forests. Elimination of all mammals resulted in much higher seed survival, and slightly higher seedling survival. Germination and seedling survival were lower at wind-exposed than at protected sites, but irrigation had no effect on dry-season seedling survival. It appears that the dominant species on Gatun Lake fragments have passed through a series of filters: seeds must first avoid being eaten by spiny rats, survive the first dry season, and then avoid seedling herbivory by rats. Biotic and abiotic factors determine seedling survival in tropical forests; synergistic changes in these factors can thus lead to dramatic losses of diversity.