Sax Dov F, Gaines Steven D, Brown James H
Department of Ecology, Evolution, and Marine Biology, University of California, Santa Barbara, California 93106, USA.
Am Nat. 2002 Dec;160(6):766-83. doi: 10.1086/343877.
Species richness is decreasing at a global scale. At subglobal scales, that is, within any defined area less extensive than the globe, species richness will increase when the number of nonnative species becoming naturalized is greater than the number of native species becoming extinct. Determining whether this has occurred is usually difficult because detailed records of species extinctions and naturalizations are rare; these records often exist, however, for oceanic islands. Here we show that species richness on oceanic islands has remained relatively unchanged for land birds, with the number of naturalizations being roughly equal to the number of extinctions, and has increased dramatically for vascular plants, with the number of naturalizations greatly exceeding the number of extinctions. In fact, for plants, the net number of species on islands has approximately doubled. We show further that these patterns are robust to differences in the history of human occupation of these islands and to the possibility of undocumented species extinctions. These results suggest that species richness may be increasing at subglobal scales for many groups and that future research should address what consequences this may have on ecological processes.
全球范围内物种丰富度正在下降。在次全球尺度上，即在任何定义的面积小于全球的区域内，当归化的非本地物种数量大于灭绝的本地物种数量时，物种丰富度将会增加。确定这种情况是否发生通常很困难，因为物种灭绝和归化的详细记录很少；然而，这些记录在海洋岛屿上往往是存在的。我们在此表明，对于陆鸟来说，海洋岛屿上的物种丰富度相对保持不变，归化物种数量大致等于灭绝物种数量；而对于维管植物来说，物种丰富度则急剧增加，归化物种数量大大超过灭绝物种数量。事实上，对于植物而言，岛屿上物种的净数量大约翻了一番。我们进一步表明，这些模式不受这些岛屿人类居住历史差异以及未记录物种灭绝可能性的影响。这些结果表明，在次全球尺度上，许多生物类群的物种丰富度可能正在增加，并且未来的研究应该探讨这可能对生态过程产生何种后果。
