Data from: Testing weed risk assessment paradigms: intraspecific differences in performance and naturalisation risk outweigh interspecific differences in alien Brassica

1.Risk assessments of alien species are usually conducted at species level, assuming that all individuals of a given species pose similar risks. However, this may not be the case if there is substantial within-species variation that could influence invasion success. 2.We used a seed addition experiment, comprising 25 taxonomically stratified varieties of three Brassica species introduced to roadside habitats in Canterbury, New Zealand, to quantify variation in performance among species, subspecies and varieties. We aimed to assess if species was the most appropriate taxonomic level at which to evaluate invasion risk. 3.Differences among varieties within species explained approximately 30 times more of the variation in performance (number of individuals/quadrat) than differences among species. Some of the variation among varieties was attributable to differences in seed viability. 4.Nevertheless, differences among taxonomic groups explained only 7% of the total variation in performance; 28% was attributable to differences among plots, reflecting broad-scale environmental variation, while 65% was attributable to differences among quadrats nested within plots, highlighting the importance of fine-scale variation in the availability of suitable microsites. 5.Policy Implications. Our seed addition experiment quantified variation in performance of 25 taxonomically stratified Brassica taxa introduced to roadside habitats. Varieties (nested within species) differed in performance far more than did species. This suggests risk assessments carried out at species level may overlook important subspecific variation in invasion risk. This is particularly true for conventionally bred and genetically modified species, which may contain taxa posing risks different to that at which the species is assessed. Consideration should be given to subjecting unassessed subspecies and varieties of plants to risk assessments similar to those applied to species.1. 外来物种风险评估通常以物种水平（species level）开展，默认同一物种种群内所有个体的入侵风险均一致。然而，若物种内存在显著影响入侵成功性的种内变异（within-species variation），则该假设可能不成立。 2. 我们以引入至新西兰坎特伯雷地区路边生境的3种芸苔属（Brassica）植物的25个按分类学分层的变种（variety）为研究对象，开展种子添加实验（seed addition experiment），以量化物种、亚种（subspecies）及变种间的生长表现差异。本研究旨在评估物种水平是否为评估入侵风险的最适分类学等级。 3. 物种内变种间的差异对生长表现（样方（quadrat）内个体数）变异的解释度约为物种种间差异的30倍。部分变种间的变异可归因于种子活力（seed viability）的差异。 4. 尽管如此，分类群间的差异仅能解释总生长表现变异的7%；28%的变异源于样地间的差异，反映了大尺度环境异质性；剩余65%则源于样地内嵌套样方间的差异，凸显了适宜微生境（microsites）可利用性的细尺度变异的重要性。 5. 政策启示。本种子添加实验量化了引入至路边生境的25个分类学分层芸苔属（Brassica）类群的生长表现变异。物种内嵌套的变种间生长表现差异远大于物种种间差异。这表明以物种水平开展的风险评估可能会忽略入侵风险中重要的亚种及种下变异。对于常规选育及转基因物种而言，这一问题尤为突出，因为此类物种可能包含与该物种整体评估风险不同的类群。因此，应考虑对未评估的植物亚种及变种开展与物种水平类似的风险评估工作。