Niche Theory and Species Range Limits Along Elevational Gradients: Perspectives and Future Directions

Despite two centuries of research, the mechanisms underlying the formation of species' elevational range limits remain poorly understood. The climatic variability hypothesis highlights the role of climatic conditions in shaping species' thermal tolerance and distribution ranges, while the species interactions-abiotic stress hypothesis underscores the relative importance of biotic factors and abiotic stress along environmental gradients. We emphasize Darwin's perspective on the ubiquity of interspecific competition across climatic gradients and the importance of understanding how climate modulates biotic interactions to shape species distributions. Niche theory provides a comprehensive framework, combined with empirical research, to explore how environmental gradients influence species traits, leading to context-dependent species interactions that constrain distributions. In particular, the application of the concept of environmentally weighted performance can further elucidate these complex ecological mechanisms. Future research should integrate multiple approaches, including field and laboratory manipulative experiments, theoretical modeling, and interdisciplinary collaboration, to improve our understanding of species distributions in mountain regions and to inform biodiversity conservation strategies in the face of rapid environmental change.