Niche and range size patterns suggest that speciation begins in small, ecologically diverged populations in North American monkeyflowers (Mimulus spp.)

Closely related species (e.g., sister taxa) often occupy very different ecological niches and can exhibit large differences in geographic distributions despite their shared evolutionary history. Budding speciation is one process that may partially explain how differences in niche and distribution characteristics may rapidly evolve. Budding speciation is the process through which new species form as initially small colonizing populations that acquire reproductive isolation. This mode of species formation predicts that, at the time of speciation, sister species should have highly asymmetrical distributions. We tested this hypothesis in North American monkeyflowers, a diverse clade with a robust phylogeny, using data on geographical ranges, climate, and plant community attributes. We found that recently diverged sister pairs have highly asymmetrical ranges and niche breadths, relative to older sister pairs. Additionally, we found that sister species occupy distinct environmental niche posi...近缘物种（如姊妹类群（sister taxa））即便拥有共同的演化历史，也常占据截然不同的生态位，且地理分布差异显著。芽生物种形成（budding speciation）是可部分解释生态位与分布特征如何快速演化的一类过程。芽生物种形成指新物种由初始小型定殖种群分化形成并获得生殖隔离（reproductive isolation）的过程。该物种形成模式预测：在物种形成当下，姊妹物种的分布应呈现高度不对称性。我们以北美沟酸浆属（North American monkeyflowers）这一物种丰富且系统发育框架稳健的类群为研究对象，结合地理分布范围、气候及植物群落属性数据对该假说进行了检验。结果发现，相较于较古老的姊妹类群对，新近分化的姊妹类群对拥有高度不对称的分布范围与生态位宽度。此外，我们发现姊妹物种占据的环境生态位位置存在显著差异……