Instituto de Ecología y Biodiversidad, Universidad de Chile, Casilla 653, Chile.
Ecology. 2011 Feb;92(2):282-8. doi: 10.1890/10-0643.1.
The abundance of exotic plants is thought to be limited by competition with resident species (including plants and generalist herbivores). In contrast, observations in semiarid Chile suggest that a native generalist rodent, the degu (Octodon degus), may be facilitating the expansion of exotic annual plants. We tested this hypothesis with a 20-year data set from a World Biosphere Reserve in mediterranean Chile. In this semiarid environment, rainfall varies annually and dramatically influences cover by both native and exotic annual plants; degu population density affects the composition and cover of exotic and native annual plants. In low-rainfall years, cover of both native and exotic herbs is extremely low. Higher levels of precipitation result in proportional increases in cover of all annual plants (exotic and native species), leading in turn to increases in degu population densities, at which point they impact native herbs in proportion to their greater cover, indirectly favoring the expansion of exotic plants. We propose that bottom-up control of consumers at our site results in top-down indirect facilitation of invasive annual herbs, and that this pattern may be general to other semiarid ecosystems.
人们认为，外来植物的丰度受到与本地物种（包括植物和一般性食草动物）竞争的限制。相比之下，智利半干旱地区的观察结果表明，本地的一般性食草啮齿动物——豚鼠（Octodon degus）可能有助于外来一年生植物的扩张。我们用智利地中海世界生物圈保护区 20 年的数据集检验了这一假说。在这种半干旱环境中，降雨量每年变化很大，极大地影响了本地和外来一年生植物的覆盖率；豚鼠种群密度影响外来和本地一年生植物的组成和覆盖率。在降雨量低的年份，本地和外来草本植物的覆盖率极低。较高的降水量会导致所有一年生植物（外来和本地物种）的覆盖率成比例增加，从而导致豚鼠种群密度增加，此时它们会根据其更大的覆盖率对本地草本植物产生影响，间接有利于外来植物的扩张。我们提出，在我们的研究地点，消费者的自下而上控制导致了对入侵性一年生草本植物的自上而下间接促进，而这种模式可能适用于其他半干旱生态系统。
