Brown J H, Valone T J, Curtin C G
Department of Biology, University of New Mexico, Albuquerque, NM 87131, USA.
Proc Natl Acad Sci U S A. 1997 Sep 2;94(18):9729-33. doi: 10.1073/pnas.94.18.9729.
Natural ecosystems contain many individuals and species interacting with each other and with their abiotic environment. Such systems can be expected to exhibit complex dynamics in which small perturbations can be amplified to cause large changes. Here, we document the reorganization of an arid ecosystem that has occurred since the late 1970s. The density of woody shrubs increased 3-fold. Several previously common animal species went locally extinct, while other previously rare species increased. While these changes are symptomatic of desertification, they were not caused by livestock grazing or drought, the principal causes of historical desertification. The changes apparently were caused by a shift in regional climate: since 1977 winter precipitation throughout the region was substantially higher than average for this century. These changes illustrate the kinds of large, unexpected responses of complex natural ecosystems that can occur in response to both natural perturbations and human activities.
自然生态系统包含许多相互作用的个体和物种，以及它们与非生物环境之间的相互作用。这样的系统预计会表现出复杂的动态变化，其中小的扰动可能会被放大，从而导致巨大的变化。在这里，我们记录了自20世纪70年代末以来发生的干旱生态系统的重组。木本灌木的密度增加了两倍。几种以前常见的动物物种在当地灭绝，而其他以前稀有的物种数量增加。虽然这些变化是荒漠化的症状，但它们并非由牲畜放牧或干旱（历史上荒漠化的主要原因）引起。这些变化显然是由区域气候的转变引起的：自1977年以来，整个地区的冬季降水量大大高于本世纪的平均水平。这些变化说明了复杂自然生态系统可能会对自然扰动和人类活动产生的那种巨大的、意想不到的反应。
