Environmental conditions can modify the intensity and sign of ecological interactions. The stress gradient hypothesis (SGH) predicts that facilitation becomes more important than competition under stressful conditions. To properly test this hypothesis, it is necessary to account for all (not a subset of) interactions occurring in the communities and consider that species do not interact at random but following a specific pattern. We aim to assess elevational changes in facilitation, in terms of species richness, frequency and intensity of the interaction as a function of the evolutionary relatedness between nurses and their associated species. We sampled nurse and their facilitated plant species in two 1000–2000 m. elevation gradients in Mediterranean Chile where low temperature imposes a mortality filter on seedlings. We first estimated the relative importance of facilitation as a mechanism adding new species to communities distributed along these gradients. We then tested whether the frequency and intensity of facilitation increases with elevation, taking into account the evolutionary relatedness of the nurse species and the facilitated species.

中文翻译：

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植物-植物促进作用随着海拔梯度的系统发育相关性降低而增加

环境条件可以改变生态相互作用的强度和迹象。压力梯度假设（SGH）预测，在压力条件下，促进比竞争更重要。为了正确检验这一假设，有必要考虑到社区中发生的所有相互作用（而不是其中的一部分），并认为物种并不是随机相互作用而是遵循特定模式。我们的目标是根据护士及其相关物种之间进化相关性的函数，根据物种的丰富性，相互作用的频率和强度来评估便利性的海拔变化。我们在两个1000–2000 m中对护士及其辅助植物进行了采样。智利地中海的海拔高度梯度，那里的低温对幼苗施加了死亡过滤器。我们首先估计了促进作用作为将新物种添加到沿这些梯度分布的社区中的机制的相对重要性。然后，我们考虑到护士物种和受助物种的进化相关性，测试了促进的频率和强度是否随海拔升高而增加。