Species interactions such as facilitation and competition play a crucial role in driving species range shifts. However, density dependence as a key feature of these processes has received little attention in both empirical and modelling studies. Herein, we used a novel, individual‐based treeline model informed by rich in situ observations to quantify the contribution of density‐dependent species interactions to alpine treeline dynamics, an iconic biome boundary recognized as an indicator of global warming. We found that competition and facilitation dominate in dense versus sparse vegetation scenarios respectively. The optimal balance between these two effects was identified at an intermediate vegetation thickness where the treeline elevation was the highest. Furthermore, treeline shift rates decreased sharply with vegetation thickness and the associated transition from positive to negative species interactions. We thus postulate that vegetation density must be considered when modelling species range dynamics to avoid inadequate predictions of its responses to climate warming.

中文翻译：

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密度依赖的物种相互作用调节高山林线变化

促进和竞争等物种相互作用在驱动物种分布范围变化方面发挥着至关重要的作用。然而，密度依赖性作为这些过程的关键特征在实证研究和建模研究中都很少受到关注。在这里，我们使用了一种新颖的、基于个体的林线模型，该模型通过丰富的现场观测来量化密度依赖的物种相互作用对高山林线动态的贡献，高山林线动态是一个标志性的生物群落边界，被认为是全球变暖的指标。我们发现竞争和促进分别在茂密和稀疏的植被场景中占主导地位。这两种效应之间的最佳平衡是在林线海拔最高的中等植被厚度处确定的。此外，随着植被厚度以及相关的从正向到负向物种相互作用的转变，林线移动率急剧下降。因此，我们假设在对物种范围动态进行建模时必须考虑植被密度，以避免对其对气候变暖的反应做出不充分的预测。