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

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.</p

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

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

How do cold-adapted plants respond to climatic cycles? Interglacial expansion explains current distribution and genomic diversity in Primula farinosa L

Understanding the effects of past climatic fluctuations on the distribution and population-size dynamics of cold-adapted species is essential for predicting their responses to ongoing global climate change. In spite of the heterogeneity of cold-adapted species, two main contrasting hypotheses have been proposed to explain their responses to Late Quaternary glacial cycles, namely, the interglacial contraction versus the interglacial expansion hypotheses. Here, we use the cold-adapted plant Primula farinosa to test two demographic models under each of the two alternative hypotheses and a fifth, null model. We first approximate the time and extent of demographic contractions and expansions during the Late Quaternary by projecting species distribution models across the last 72 ka. We also generate genome-wide sequence data using a Reduced Representation Library approach to reconstruct the spatial structure, genetic diversity, and phylogenetic relationships of lineages within P. farinosa. Finally, by integrating the results of climatic and genomic analyses in an Approximate Bayesian Computation framework, we propose the most likely model for the extent and direction of population-size changes in P. farinosa through the Late Quaternary. Our results support the interglacial expansion of P. farinosa, differing from the prevailing paradigm that the observed distribution of cold-adapted species currently fragmented in high altitude and latitude regions reflects the consequences of postglacial contraction processes. [Approximate Bayesian computation; climate change; hindcasting; Late Quaternary glacial cycles; paleoclimate; Reduced Representation Library; species distribution models.