Department of Biology, McGill University, Montreal, Canada.
PLoS One. 2012;7(8):e44555. doi: 10.1371/journal.pone.0044555. Epub 2012 Aug 30.
While the effect of habitat connectivity on local and regional diversity has been analysed in a number of studies, time-dependent dynamics in metacommunities have received comparatively little consideration. When local patches of a metacommunity are identical in environmental conditions but differ in initial community composition, dispersal among patches may result in homogenization of local communities. In a microcosm experiment with benthic ciliates, we tested the hypothesis that the effect of connectivity on diversity is time-dependent and only transitory, with the degree of connectivity affecting the time to homogenization but not the final outcome. Six microcosms were connected to a metacommunity with one of three levels of connectivity. The six patches differed in initial community composition but were identical in environmental conditions. We found a time-dependent and transitory effect of connectivity on local and regional richness and on local Shannon diversity, while Bray-Curtis dissimilarity and regional Shannon diversity were persistently affected by connectivity. Local richness increased and regional richness decreased with connectivity during the initial phase of the experiment but soon converged to similar values in all three connectivity treatments. Local Shannon diversity was unimodally related to time, with maximum diversity reached sooner with high than with medium or low connectivity. Eventually, however, local diversity converged to similar values irrespective of connectivity. At the regional scale, Shannon diversity was persistently lower with high than with low connectivity. While initial differences in community composition vanished with medium and high connectivity, they were maintained with low connectivity resulting in persistently high beta and regional diversity. The effect of connectivity on ciliate community composition translated down to the algal resource, as stronger dominance of the superior competitor with high and medium connectivity resulted in stronger depletion of the resource.
虽然已有许多研究分析了生境连通性对局部和区域多样性的影响，但后生境群落的时变动态却得到了相对较少的关注。当后生境群落的局部斑块在环境条件上相同时，但在初始群落组成上存在差异时，斑块间的扩散可能导致局部群落同质化。在一个以底栖纤毛虫为对象的微宇宙实验中，我们检验了这样一个假设，即连通性对多样性的影响是时变的且是暂时的，连通度的程度会影响到同质化的时间，但不会影响最终结果。六个微宇宙与一个具有三种连通度水平的后生境群落相连。这六个斑块在初始群落组成上存在差异，但在环境条件上是相同的。我们发现，连通度对局部和区域丰富度以及局部 Shannon 多样性具有时变的和暂时的影响，而 Bray-Curtis 不相似性和区域 Shannon 多样性则持续受到连通度的影响。在实验的初始阶段，连通度对局部丰富度和区域丰富度有时间依赖性和暂时的影响，但很快在所有三种连通度处理中 converged 到相似的值。局部 Shannon 多样性与时间呈单峰关系，高连通度下达到最大多样性的时间早于中连通度和低连通度。然而，最终局部多样性 converged 到相似的值，而与连通度无关。在区域尺度上，Shannon 多样性持续低于高连通度和低连通度。虽然在中连通度和高连通度下，群落组成的初始差异消失了，但在低连通度下，这些差异仍然存在，导致持续的高 beta 和区域多样性。连通度对纤毛虫群落组成的影响也反映在藻类资源上，因为高连通度和中连通度下，优势竞争者的优势更强，导致资源的消耗更严重。
