Faculty of Science, Institute for Environmental Studies, Charles University, Prague, Czech Republic.
Department of Zoology and Laboratory of Ornithology, Faculty of Science, Palacky University, Olomouc, Czech Republic.
J Anim Ecol. 2018 May;87(3):774-789. doi: 10.1111/1365-2656.12808. Epub 2018 Mar 6.
The role of interspecific competition for generating patterns in species' distribution is hotly debated and studies taking into account processes occurring at both large and small spatial scales are almost missing. Theoretically, competition between species with overlapping niches should result in divergence of their niches in sympatry to reduce the costs of competition. Many species show a mosaic distribution within sympatric zones, with the syntopic sites occupied by both species, and allotopic sites where only one species occurs. It is unclear whether such mosaics arise as a consequence of competition-driven niche segregation or due to the decline of their abundances towards range edges driven by environmental gradients. If the interspecific competition matters, we should observe (1) a shift in habitat preferences of one or both species between syntopy and allotopy, and (2) between allopatry and allotopy. Moreover, (3) species should show greater divergence in their habitat preferences in allotopy than in allopatry where (4) no differences in habitat preferences may occur. Finally, (5) shifts should be generally greater in the competitively subordinate species than in the dominant species. We used a unique dataset on abundance of two closely related passerine species, the Common Nightingale (Luscinia megarhynchos) and the Thrush Nightingale (Luscinia luscinia), collected across their syntopy, allotopy and allopatry. The predictions were tested within a generalized mixed-effects modelling framework. After accounting for environmental gradients perpendicular to the species' contact zone, we found a strong support for all but one prediction. Habitat preferences of both species shifted markedly between syntopy and allotopy, as well as between allopatry and allotopy. Whereas the species preferred the same habitats in allopatry, their preferences became strikingly different in allotopy where the abundance of the Common Nightingale increased towards dry and warm sites with low coverage of pastures, while the abundance of the Thrush Nightingale showed exactly opposite trends. Fifth prediction was not supported. Our results indicate that the competition between closely related species can result in considerable changes in habitat use across their geographic ranges accompanied with divergence in their habitat preferences in sympatry. Here, the species "escape" from competition to allotopic sites covered by habitats avoided by the competitor. Therefore, we argue that the interspecific competition is an important driver of species' distribution at both large and small spatial scales.
种间竞争在物种分布模式形成中的作用是一个备受争议的话题，而几乎没有考虑到大尺度和小尺度过程的研究。理论上，具有重叠生态位的物种之间的竞争应该导致它们在同域中的生态位分歧，以减少竞争的代价。许多物种在同域区表现出镶嵌分布，即在同域区既有两个物种的共位点，也有只有一个物种存在的异位点。目前还不清楚这种镶嵌现象是竞争驱动的生态位分离的结果，还是由于环境梯度导致的物种丰度向分布范围边缘下降的结果。如果种间竞争很重要，我们应该观察到（1）一个或两个物种在同域和异位之间的栖息地偏好发生变化，（2）在异域和异位之间。此外，（3）物种在异位时的栖息地偏好应该比在异域时表现出更大的差异，在异域时（4）可能不会出现栖息地偏好的差异。最后，（5）变化在竞争劣势物种中通常会大于在优势物种中。我们使用了一个独特的数据集，该数据集记录了两种密切相关的雀形目鸟类，普通夜莺（Luscinia megarhynchos）和画眉夜莺（Luscinia luscinia）的丰度，这些鸟类分布在它们的同域、异位和异域。这些预测在广义混合效应建模框架内进行了测试。在考虑到垂直于物种接触带的环境梯度后，我们发现除了一个预测外，其他预测都得到了强有力的支持。这两种物种的栖息地偏好都在同域和异位之间以及异域和异位之间发生了显著变化。尽管这两个物种在异域时偏好相同的栖息地，但在异位时，它们的偏好变得截然不同，普通夜莺的数量在干燥和温暖的地方增加，这些地方的牧场覆盖率较低，而画眉夜莺的数量则正好相反。第五个预测没有得到支持。我们的结果表明，亲缘关系密切的物种之间的竞争会导致它们在地理分布范围内的栖息地利用发生相当大的变化，并伴随着它们在同域中的生态位偏好的分歧。在这里，物种“逃避”到由竞争者避免的生境组成的异位点。因此，我们认为种间竞争是大尺度和小尺度物种分布的重要驱动因素。
