PDF(Pubmed)
Abstract：
Dominant vegetation in many ecosystems is an integral component of structure and habitat. In many drylands, native shrubs function as foundation species that benefit other plants and animals. However, invasive exotic plant species can comprise a significant proportion of the vegetation. In Central California drylands, the facilitative shrub Ephedra californica and the invasive Bromus rubens are widely dispersed and common. Using comprehensive survey data structured by shrub and open gaps for the region, we compared network structure with and without this native shrub canopy and with and without the invasive brome. The presence of the invasive brome profoundly shifted the network measure of centrality in the microsites structured by a shrub canopy (centrality scores increased from 4.3 under shrubs without brome to 6.3, i.e. a relative increase of 42%). This strongly suggests that plant species such as brome can undermine the positive and stabilizing effects of native foundation plant species provided by shrubs in drylands by changing the frequency that the remaining species connect to one another. The net proportion of positive and negative associations was consistent across all microsites (approximately 50% with a total of 14% non-random co-occurrences on average) suggesting that these plant-plant networks are rewired but not more negative. Maintaining resilience in biodiversity thus needs to capitalize on protecting native shrubs whilst also controlling invasive grass species particularly when associated with shrubs.
摘要：
许多生态系统中的优势植被是结构和栖息地的组成部分。在许多旱地,本地灌木作为基础物种，有利于其他植物和动物。然而,外来入侵植物物种可以占植被的很大比例。在加州中部的旱地,促生灌木加州麻黄和浸润性棕草分布广泛且常见。利用该地区灌木和开放缺口构成的综合调查数据，我们比较了有和没有这种原生灌木冠层以及有和没有侵入性树冠的网络结构。侵入性溴化物的存在深刻地改变了由灌木冠层构成的微站点中中心性的网络度量（中心性得分从无溴化物的灌木下的4.3增加到6.3，即相对增加了42％）。这强烈表明，通过改变其余物种彼此连接的频率，诸如brome之类的植物物种可以破坏旱地灌木提供的本地基础植物物种的积极和稳定作用。正和负关联的净比例在所有微站点中都是一致的（平均约50％，总共有14％的非随机共现），这表明这些植物-植物网络被重新布线，但没有更多的负关联。因此，保持生物多样性的复原力需要利用保护本地灌木，同时还控制入侵草物种，特别是与灌木相关的入侵草物种。
