Seabloom Eric W, Harpole W Stanley, Reichman O J, Tilman David
National Center for Ecological Analysis and Synthesis, 735 State Street, Santa Barbara, CA 93103, USA.
Proc Natl Acad Sci U S A. 2003 Nov 11;100(23):13384-9. doi: 10.1073/pnas.1835728100. Epub 2003 Oct 31.
The dynamics of invasive species may depend on their abilities to compete for resources and exploit disturbances relative to the abilities of native species. We test this hypothesis and explore its implications for the restoration of native ecosystems in one of the most dramatic ecological invasions worldwide, the replacement of native perennial grasses by exotic annual grasses and forbs in 9.2 million hectares of California grasslands. The long-term persistence of these exotic annuals has been thought to imply that the exotics are superior competitors. However, seed-addition experiments in a southern California grassland revealed that native perennial species, which had lower requirements for deep soil water, soil nitrate, and light, were strong competitors, and they markedly depressed the abundance and fecundity of exotic annuals after overcoming recruitment limitations. Native species reinvaded exotic grasslands across experimentally imposed nitrogen, water, and disturbance gradients. Thus, exotic annuals are not superior competitors but rather may dominate because of prior disturbance and the low dispersal abilities and extreme current rarity of native perennials. If our results prove to be general, it may be feasible to restore native California grassland flora to at least parts of its former range.
入侵物种的动态变化可能取决于它们相对于本地物种在争夺资源和利用干扰方面的能力。我们检验了这一假设，并探讨了其对于全球最严重的生态入侵之一中本地生态系统恢复的影响，即在加利福尼亚州920万公顷的草原上，外来一年生禾本科植物和杂草取代了本地多年生禾本科植物。这些外来一年生植物的长期存续一直被认为意味着它们是更具优势的竞争者。然而，南加利福尼亚州一片草原上的种子添加实验表明，对深层土壤水分、土壤硝酸盐和光照需求较低的本地多年生物种是强大的竞争者，在克服了幼苗补充限制后，它们显著降低了外来一年生植物的数量和繁殖力。本地物种在实验设定的氮、水和干扰梯度下重新侵入了外来草地。因此，外来一年生植物并非更具优势的竞争者，而是可能由于先前的干扰以及本地多年生植物的低扩散能力和当前的极度稀少而占据主导地位。如果我们的结果具有普遍性，那么将加利福尼亚州本地草原植物群落恢复到其以前分布范围的至少一部分可能是可行的。
