Data from: Non-linear effects of phylogenetic distance on early-stage establishment of experimentally introduced plants in grassland communities

1. The phylogenetic distance of an introduced plant species to a resident native community may play a role in determining its establishment success. While Darwin’s naturalization hypothesis predicts a positive relationship, the preadaptation hypothesis predicts a negative relationship. Rigorous tests of this now so-called Darwin’s naturalization conundrum require not only information on establishment successes but also of failures, which is frequently not available. Such essential information, however, can be provided by experimental introductions. 2. Here, we analysed three datasets from two field experiments in Germany and Switzerland. In the Swiss experiment, alien and native grassland species were introduced as seeds only with and without disturbance (tilling). In the German experiment, alien and native grassland species were introduced both as seeds and as seedlings with and without disturbance (tilling), and with and without fungicide application. For the seedling introduction experiment, there was an additional herbivore-exclusion treatment. 3. Phylogenetic distance affected establishment in the three datasets differently, with success peaking at intermediate distances for the seed datasets, but decreasing with increasing distances in the seedling dataset. Disturbance favored seedling survival, most likely by weakening the resident community. 4. Synthesis: By analyzing experimental introductions, we show that the relationship between phylogenetic distance and establishment, at least for seedling emergence, may actually be non-linear with an optimum at intermediate distances. Therefore, Darwin´s naturalization hypothesis and the preadaptation hypothesis need not be in conflict. Rather, the mechanisms underlying them can operate simultaneously or alternately depending on the life stage and on the environmental conditions of the resident community.

1. 引入植物物种与本地常驻群落之间的系统发育距离（phylogenetic distance），可能会对其定殖成功与否产生影响。达尔文归化假说（Darwin’s naturalization hypothesis）预测二者呈正相关关系，而预适应假说（preadaptation hypothesis）则预测二者呈负相关关系。针对这一如今被称为“达尔文归化谜题”的科学问题开展严谨检验，不仅需要获取定殖成功的相关信息，还需要定殖失败的对应数据，而此类数据往往难以通过常规途径获取。不过，实验引种（experimental introductions）能够提供这类关键信息。
2. 本研究分析了源自德国与瑞士的两项野外实验的三套数据集。在瑞士的实验中，研究人员仅通过种子途径引入外来与本地草原植物物种，并设置了干扰（disturbance，即翻耕）与无干扰两组处理。在德国的实验中，研究人员同时通过种子与幼苗两种方式引入外来与本地草原植物物种，设置了翻耕干扰与无干扰、施用杀菌剂与不施用杀菌剂四组处理；针对幼苗引种实验，还额外增设了植食动物排除处理组。
3. 三套数据集显示，系统发育距离对定殖的影响存在显著差异：种子数据集的定殖成功率在中等距离处达到峰值，而幼苗数据集的定殖成功率则随距离增加而持续下降。翻耕干扰有利于幼苗存活，其机制大概率是削弱了本地常驻群落的竞争能力。
4. 研究总结：通过分析实验引种数据，本研究表明，系统发育距离与定殖成功率之间的关系（至少针对幼苗出苗阶段而言）可能呈非线性特征，且在中等距离处存在最优值。因此，达尔文归化假说与预适应假说并非必然对立。二者背后的作用机制可根据生物的生活史阶段以及本地群落的环境条件，同时或交替发挥作用。