Historical and contemporary climate jointly determines seed plant diversity patterns in eastern Eurasia

Large-scale spatial patterns of species richness are one of the central issues in ecology. Although hypotheses based on effects of contemporary climate, evolutionary history and historical climate change have been employed to explain the mechanisms underlying species richness patterns, variation in relative contribution of different hypothesis remains a major challenge. Here, using newly-compiled distribution data with a spatial resolution of 100 * 100 km2 for 43,023 seed plant species in eastern Eurasia, we mapped species richness patterns for plants with different growth forms (i.e., woody vs. herbaceous) and range sizes (i.e., wide-ranged vs. narrow-ranged species), and compared the contribution of four hypotheses on these patterns, i.e., freezing tolerance hypothesis, historical climate change hypothesis, Janzen hypothesis and diversification rate hypothesis. We found that species richness of all seed plants presented a clear latitudinal gradient and was the highest in southwestern China and Central Asian mountains. Notably, species richness patterns and their dominant hypotheses differed between species groups. Historical climate change dominated richness patterns of overall, herbaceous and wide-ranged herbaceous species. The freezing tolerance hypothesis dominated those for all woody and wide-ranged woody species, while the Janzen hypothesis dominated narrow-ranged woody and herbaceous species. Our study suggests that different hypotheses contribute to large-scale species richness patterns via their dominant effects in different species groups. Interestingly, our study did not support the diversification rate hypothesis, but demonstrated high contribution of historical climate change to plant diversity, providing new perspectives on the mechanisms of plant diversity patterns in eastern Eurasia.