Department of Integrative Biology, University of Texas at Austin, Austin, TX, United States of America.
Wildlife Conservation Society, Bronx, NY, United States of America.
PLoS One. 2019 Jul 10;14(7):e0217549. doi: 10.1371/journal.pone.0217549. eCollection 2019.
The degree to which interspecific competition structures diverse communities is an oft-debated topic. An approach to answering this question is to examine spatial patterns of coexistence among putatively competing species. The degree to which interspecies competition predominates in a community can have important effects on our ability predict the response of that community to perturbations, most notably climate change, when shifting species' ranges may result in novel species assemblages. We present a study on the avifauna of the Eastern Himalayas. We hypothesize that in a community where competitive interactions predominate, there will be a relationship between pairwise altitudinal overlaps and morphological differences between species. Moreover, we hypothesize that both morphological traits and altitudinal traits depart from a Brownian motion evolution model, resulting in species trait covariances having a phylogenetic component. We find a significant relationship between morphological dissimilarity and altitudinal overlaps of species pairs. We also find that closely related species are significantly more altitudinally stratified than a null model would predict. However, as more distantly related species pairs are included in the analysis, this pattern disappears, indicating that competitive interactions predominate only in closely related species. This is further suggested by the fact that altitudinal ranges themselves are phylogenetically overdispersed at the genus level, as are morphological traits. This effect disappears when the entire phylogeny is examined, with morphology and altitude being phylogenetically underdispersed. Model fitting suggests that individual clades have evolved towards local clade-specific fitness peaks, while within-clade results show evidence of niche partitioning. We interpret these results as a tension between competition on shorter time scales and selection on longer time scales, where competition forces closely-related species away from fitness peaks in order to allow for niche separation and hence coexistence, suggesting that this effect is partially responsible for the recent diversification of Eastern Himalayan avifauna.
种间竞争在多大程度上构建了多样化的群落是一个经常被讨论的话题。回答这个问题的一种方法是研究假定竞争物种之间共存的空间模式。在一个群落中，种间竞争的程度对我们预测该群落对干扰的反应能力有重要影响，尤其是气候变化，当物种的分布范围发生变化时，可能会导致新的物种组合。我们提出了一项关于东喜马拉雅地区鸟类的研究。我们假设，在一个竞争作用占主导地位的群落中，物种之间的成对海拔重叠和形态差异之间将存在关系。此外，我们假设形态特征和海拔特征偏离布朗运动进化模型，导致物种特征协方差具有系统发育成分。我们发现物种对之间的形态差异与海拔重叠之间存在显著关系。我们还发现，与一个空模型预测的结果相比，亲缘关系密切的物种在海拔上的分层更为明显。然而，当更多的远缘物种对被纳入分析时，这种模式就消失了，这表明竞争作用只在亲缘关系密切的物种中占主导地位。这进一步表明，海拔范围本身在属级水平上表现出系统发育过度分散，形态特征也是如此。当整个系统发育树被检查时，这种效果就消失了，形态和海拔表现出系统发育下分散。模型拟合表明，个别分支进化到了局部分支特异性的适应峰，而分支内的结果则显示出生态位划分的证据。我们将这些结果解释为短时间尺度上的竞争和长时间尺度上的选择之间的紧张关系，在这种关系中，竞争迫使亲缘关系密切的物种远离适应峰，以允许生态位分离，从而共存，这表明这种效应部分解释了东喜马拉雅地区鸟类近期多样化的原因。
