Competition contributes to both warm and cool range edges

Competition plays an important role in shaping species’ spatial distributions. However, it remains unclear where and how competition regulates species’ range limits. In an experiment with plants originating from low and high elevations and conducted across an elevation gradient in the Swiss Alps, we find that both lowland and highland species can better persist in the presence of competition within, rather than beyond, their elevation ranges. These suggest that competition helps set both lower and upper elevation range limits of these species. Furthermore, the reduced ability of pairs of lowland or highland species to coexist beyond their range edges is mainly driven by diminishing niche differences; changes in both niche differences and relative fitness differences drive weakening competitive dominance of lowland over highland species with increasing elevation. These results highlight the need to account for competitive interactions and investigate underlying coexistence mechanisms to understand current and future species distributions.

种间竞争在塑造物种空间分布格局中发挥着关键作用。然而，目前尚不清楚竞争是通过何种路径、在哪些区域调控物种的分布范围极限。本研究依托瑞士阿尔卑斯山脉的海拔梯度开展野外实验，实验材料取自低海拔与高海拔生境的植物种群，结果显示：无论低地物种还是高地物种，在其自身海拔分布范围内遭遇种间竞争时，种群存续状况均优于分布范围之外的情形。这表明种间竞争共同参与设定了这些物种的海拔分布上下限。此外，低地或高地物种种对在其分布范围边缘之外的共存能力出现下降，这一现象主要由生态位差异（niche differences）的缩减所驱动；随着海拔升高，生态位差异与相对适合度差异（relative fitness differences）的共同变化，导致低地物种相较于高地物种的竞争优势逐步削弱。本研究结果凸显：若要明晰物种当前及未来的分布格局，必须纳入种间竞争相互作用的考量，并深入探究物种共存的内在机制。