Department of Organismic Biology, University of Salzburg, Salzburg, Austria.
PLoS One. 2011;6(12):e29071. doi: 10.1371/journal.pone.0029071. Epub 2011 Dec 16.
Linking local communities to a metacommunity can positively affect diversity by enabling immigration of dispersal-limited species and maintenance of sink populations. However, connectivity can also negatively affect diversity by allowing the spread of strong competitors or predators. In a microcosm experiment with five ciliate species as prey and a copepod as an efficient generalist predator, we analysed the effect of connectivity on prey species richness in metacommunities that were either unconnected, connected for the prey, or connected for both prey and predator. Presence and absence of predator dispersal was cross-classified with low and high connectivity. The effect of connectivity on local and regional richness strongly depended on whether corridors were open for the predator. Local richness was initially positively affected by connectivity through rescue of species from stochastic extinctions. With predator dispersal, however, this positive effect soon turned negative as the predator spread over the metacommunity. Regional richness was unaffected by connectivity when local communities were connected only for the prey, while predator dispersal resulted in a pronounced decrease of regional richness. The level of connectivity influenced the speed of richness decline, with regional species extinctions being delayed for one week in weakly connected metacommunities. While connectivity enabled rescue of prey species from stochastic extinctions, deterministic extinctions due to predation were not overcome through reimmigration from predator-free refuges. Prey reimmigrating into these sink habitats appeared to be directly converted into increased predator abundance. Connectivity thus had a positive effect on the predator, even when the predator was not dispersing itself. Our study illustrates that dispersal of a species with strong negative effects on other community members shapes the dispersal-diversity relationship. When connections enable the spread of a generalist predator, positive effects of connectivity on prey species richness are outweighed by regional extinctions through predation.
将本地社区与超社区联系起来可以通过促进扩散受限物种的移民和维持汇种群来积极影响多样性。然而，连通性也可以通过允许强竞争者或捕食者的传播而对多样性产生负面影响。在一项以五个纤毛虫物种为猎物和一个桡足类作为高效泛食性捕食者的微宇宙实验中，我们分析了连通性对超社区中猎物物种丰富度的影响，这些超社区要么没有连接，要么只连接了猎物，要么同时连接了猎物和捕食者。捕食者扩散的存在与否与低和高连通性交叉分类。连通性对本地和区域丰富度的影响强烈取决于捕食者是否可以通过走廊扩散。通过拯救物种免受随机灭绝，连通性最初对本地丰富度产生积极影响。然而，随着捕食者在超社区中扩散，这种积极影响很快变为负面，因为捕食者传播。当本地社区仅与猎物相连时，连通性对区域丰富度没有影响，而捕食者的扩散则导致区域丰富度明显下降。连通性水平影响丰富度下降的速度，在弱连通的超社区中，区域物种灭绝延迟了一周。虽然连通性使猎物物种能够从随机灭绝中获救，但由于捕食而导致的确定性灭绝并不能通过从无捕食者避难所重新移民来克服。重新移民到这些汇栖息地的猎物似乎直接转化为增加的捕食者数量。即使捕食者本身没有扩散，连通性对捕食者也有积极影响。我们的研究表明，具有强烈负面影响的物种的扩散会影响扩散多样性关系。当连接使泛食性捕食者传播时，连通性对猎物物种丰富度的积极影响会被捕食导致的区域灭绝所抵消。
