Competition is a prominent mechanism driving population dynamics and structuring community assemblage, which can be investigated by linking shifts in species’ ecological niche and the densities of sympatric species because the ecological release from competitive constraints is a density-dependent process. In this work we determine how a steppe passerine community segregates their ecological niches and evaluate the role of competition in inducing changes in the ecological niche of species. We built multidimensional ecological niches (with Gaussian kernel density estimators) using data on the habitat features used by 10 bird species collected from seven sites in the natural steppes of Central Spain over 2 consecutive years. We computed distance and niche similarity metrics to explore the ecological niche partitioning of the bird community. Next, we ran multivariate linear regression models to evaluate the effects of conspecific and heterospecific density (as proxies of intraspecific and interspecific competition, respectively) on niche breadth and/or position of the three most abundant species. We found low niche overlap in the community assemblage but varying levels of niche similarity among pairs of species, which could increase the likelihood of current competition operating in the community. However, we found no effect of heterospecific density on niche breadth or position, although conspecific density was negatively related to niche breadth. Contrary to predictions of competition theory, increased density of conspecifics caused niche contraction. Our results from a multispecies system contribute to advanced knowledge of the biotic mechanisms structuring wildlife communities within the framework of ecological niche theory.

中文翻译：

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同种密度的增加导致多特异性雀形目动物组合中的生态位收缩

竞争是驱动种群动态和构建群落组合的重要机制，可以通过将物种生态位的变化与同域物种的密度联系起来进行研究，因为竞争约束的生态释放是一个密度依赖的过程。在这项工作中，我们确定了草原雀形目群落如何隔离其生态位，并评估竞争在诱导物种生态位变化中的作用。我们利用连续两年从西班牙中部自然草原七个地点收集的 10 种鸟类的栖息地特征数据，构建了多维生态位（使用高斯核密度估计器）。我们计算距离和生态位相似性度量来探索鸟类群落的生态位划分。接下来，我们运行多元线性回归模型来评估同种和异种密度（分别作为种内和种间竞争的代表）对三种最丰富物种的生态位宽度和/或位置的影响。我们发现群落组合中的生态位重叠度较低，但物种对之间的生态位相似性程度不同，这可能会增加群落中当前竞争的可能性。然而，我们发现异种密度对生态位宽度或位置没有影响，尽管同种密度与生态位宽度负相关。与竞争理论的预测相反，同种密度的增加导致生态位收缩。我们来自多物种系统的结果有助于在生态位理论框架内构建野生动物群落的生物机制的先进知识。