Department of Organismic Biology, University of Salzburg, Salzburg, Austria.
Oecologia. 2011 Nov;167(3):723-32. doi: 10.1007/s00442-011-2013-1. Epub 2011 May 18.
There is considerable theoretical evidence that a trade-off between competitive and colonization ability enables species coexistence. However, empirical studies testing for the presence of a competition-colonization (CC) trade-off and its importance for species coexistence have found mixed results. In a microcosm experiment, we looked for a CC trade-off in a community of six benthic ciliate species. For each species, we measured the time needed to actively disperse to and colonize an empty microcosm. By measuring dispersal rates and growth rates of the species, we were able to differentiate between these two important components of colonization ability. Competitive ability was investigated by comparing species' growth with or without a competitor in all pairwise species combinations. Species significantly differed in their colonization abilities, with good colonizers having either high growth rates or high dispersal rates or both. Although species showed a clear competitive hierarchy, competitive and colonization ability were uncorrelated. The weakest competitors were also the weakest colonizers, and the strongest competitor was an intermediate colonizer. However, some of the inferior competitors had higher colonization abilities than the strongest competitor, indicating that a CC trade-off may enable coexistence for a subset of the species. Absence of a community-wide CC trade-off may be based on the lack of strong relationships between the traits underlying competitive and colonization ability. We show that temporal effects and differential resource use are alternative mechanisms of coexistence for the species that were both slow colonizers and poor competitors.
有相当多的理论证据表明，竞争能力和定植能力之间的权衡关系使物种能够共存。然而，检验竞争-定植权衡关系是否存在及其对物种共存的重要性的实证研究得出了混合的结果。在一个微宇宙实验中，我们研究了六种底栖纤毛虫物种群落中的竞争-定植权衡关系。对于每个物种，我们测量了主动扩散到空微宇宙并定植所需的时间。通过测量物种的扩散率和增长率，我们能够区分定植能力的这两个重要组成部分。通过在所有两两物种组合中比较有或没有竞争者时的物种生长情况，研究了竞争能力。物种在定植能力上存在显著差异，良好的定植者要么具有高生长率，要么具有高扩散率，或者两者兼而有之。尽管物种表现出明显的竞争层次结构，但竞争和定植能力之间没有相关性。最弱的竞争者也是最弱的定植者，而最强的竞争者是中等定植者。然而，一些较弱的竞争者具有比最强的竞争者更高的定植能力，这表明竞争-定植权衡关系可能使一部分物种共存。群落范围内不存在竞争-定植权衡关系可能基于竞争和定植能力的基础性状之间缺乏强关系。我们表明，对于那些既是缓慢定植者又是竞争弱者的物种，时间效应和差异资源利用是共存的替代机制。
