Data from: Why close relatives make bad neighbors: phylogenetic conservatism in niche preferences and dispersal disproves Darwin’s Naturalization Hypothesis in the thistle tribe

The number of exotic plant species that have been introduced into the United States far exceeds that of other groups of organisms, and many of these have become invasive. As in many regions of the globe, invasive members of the thistle tribe, Cardueae, are highly problematic in the California Floristic Province, an established biodiversity hotspot. While Darwin's naturalization hypothesis posits that plant invaders closely related to native species would be at a disadvantage, evidence has been found that introduced thistles more closely related to native species are more likely to become invasive. To elucidate the mechanisms behind this pattern, we modelled the ecological niches of thistle species present in the province and compared niche similarity between taxa and their evolutionary relatedness, using fossil-calibrated molecular phylogenies of the tribe. The predicted niches of invasive species were found to have higher degrees of overlap with native species than noninvasive introduced species do, and pairwise niche distance was significantly correlated with phylogenetic distance, suggesting phylogenetic niche conservatism. Invasive thistles also displayed superior dispersal capabilities compared to noninvasive introduced species, and these capabilities exhibited a phylogenetic signal. By analysing the modelled ecological niches and dispersal capabilities of over a hundred thistle species, we demonstrate that exapted preferences to the invaded environment may explain why close exotic relatives may make bad neighbours in the thistle tribe.引入美国的外来植物物种数量远超其他生物类群，且其中多数已演变为入侵物种。与全球多数区域一样，蓟族（Cardueae）的入侵类群在加州植物区省（California Floristic Province）——这一公认的生物多样性热点区域——内造成的危害尤为严重。达尔文归化假说（Darwin's naturalization hypothesis）指出，与本土物种亲缘关系紧密的植物入侵者将处于竞争劣势，但现有研究证据显示，与本土物种亲缘关系更接近的外来蓟族植物，反而更易成为入侵物种。为阐明该现象背后的作用机制，本研究以蓟族的化石校准分子系统发育树为依据，对该区域内蓟类物种的生态位开展建模，并对比各分类群间的生态位相似度与其演化亲缘关系。研究结果表明，入侵物种的预测生态位与本土物种的生态位重叠程度，显著高于非入侵性外来物种；且成对生态位距离与系统发育距离呈显著相关，这印证了系统发育生态位保守性（phylogenetic niche conservatism）的存在。相较于非入侵性外来蓟类，入侵蓟类还具备更优越的扩散能力，且这类扩散能力存在系统发育信号（phylogenetic signal）。通过对百余种蓟类物种的建模生态位与扩散能力进行分析，本研究证实：对入侵环境的预适应偏好，或可解释为何亲缘关系较近的外来蓟族植物会成为“糟糕的邻者”。