What drives species’ distributions along elevational gradients? Macroecological and ‐evolutionary insights from Brassicaceae of the central Alps

Abstract

Abstract Aim Geographic distribution limits of organisms are often affected by climate, but little is known of how the impacts of climate evolve within sets of related taxa. Here we identified the climate variables most closely associated with low‐elevation limits, optimal elevations, and high‐elevation limits of plant species’ distributions and compared evolutionary lability of niche values predicting the three aspects of distribution best. Location Central Alps. Time period Current. Major taxa studied The plant family Brassicaceae. Methods We modelled the occurrence of 110 brassicaceous species in the central European Alps and used response curves of predicted occurrence on climatic variables to reveal those variables most strongly associated with elevational distribution. We produced a phylogeny of the species, applied phylogenetic comparative analysis and tested whether niche values predicting the low and high limits and the optimum of elevational distribution were similar among related taxa. Results Upper limits were closely associated with the length of the vegetation season for the majority of species, while summer or spring temperatures were strongly allied with both the occurrence optimum and the lower limit. Furthermore, niche values predicting the upper limit and the optimum of elevational distribution were less conserved in contrast to niche values predicting the lower limit of distribution. Main conclusions These results highlight constraints on adaptation at the warm end of the climate niche and may explain observed range retractions at warm range edges due to ongoing climate change.