Davies Kendi F, Harrison Susan, Safford Hugh D, Viers Joshua H
Department of Environmental Science and Policy, University of California, Davis, California, USA.
Ecology. 2007 Aug;88(8):1940-7. doi: 10.1890/06-1907.1.
At small scales, areas with high native diversity are often resistant to invasion, while at large scales, areas with more native species harbor more exotic species, suggesting that different processes control the relationship between native and exotic species diversity at different spatial scales. Although the small-scale negative relationship between native and exotic diversity has a satisfactory explanation, we lack a mechanistic explanation for the change in relationship to positive at large scales. We investigated the native-exotic diversity relationship at three scales (range: 1-4000 km2) in California serpentine, a system with a wide range in the productivity of sites from harsh to lush. Native and exotic diversity were positively correlated at all three scales; it is rarer to detect a positive relationship at the small scales within which interactions between individuals occur. However, although positively correlated on average, the small-scale relationship between native and exotic diversity was positive at low-productivity sites and negative at high-productivity sites. Thus, the change in the relationship between native and exotic diversity does not depend on spatial scale per se, but occurs whenever environmental conditions change to promote species coexistence rather than competitive exclusion. This occurred within a single spatial scale when the environment shifted from being locally unproductive to productive.
在小尺度上，本地多样性高的区域通常对入侵具有抗性，而在大尺度上，本地物种较多的区域容纳的外来物种也更多，这表明不同的过程在不同空间尺度上控制着本地物种和外来物种多样性之间的关系。虽然本地与外来多样性之间的小尺度负相关关系有一个令人满意的解释，但我们缺乏一个关于这种关系在大尺度上转变为正相关的机制性解释。我们在加利福尼亚蛇纹石地区的三个尺度（范围：1 - 4000平方公里）上研究了本地与外来多样性的关系，该系统中不同地点的生产力范围很广，从恶劣到繁茂。本地和外来多样性在所有三个尺度上都呈正相关；在个体间相互作用发生的小尺度上检测到正相关关系的情况更为罕见。然而，尽管总体上呈正相关，但本地与外来多样性之间的小尺度关系在低生产力地点为正，在高生产力地点为负。因此，本地与外来多样性关系的变化并不取决于空间尺度本身，而是每当环境条件发生变化以促进物种共存而非竞争排斥时就会发生。当环境从局部低生产力转变为高生产力时，这种情况在单一空间尺度内就会出现。
