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（alien species）的风险评估通常以物种水平开展，默认假定某一给定物种的所有个体均具有相似的风险。然而，若存在显著影响入侵成功（invasion success）的种内变异（within-species variation），这一假定可能并不成立。 2. 本研究采用种子添加实验（seed addition experiment），选取引入至新西兰坎特伯雷（Canterbury）路边生境（roadside habitats）的3个芸苔属（Brassica）物种下共25个按分类学分层的品种，以量化物种、亚种（subspecies）及品种间的表现差异。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层级。 3. 物种内各品种间的差异对表现变异的解释度约为物种间差异的30倍（表现以样方（quadrat）内个体数计）。部分品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（taxonomic groups）间的差异仅能解释总表现变异的7%；28%的变异归因于样地（plots）间的差异，反映了大尺度环境变异，而65%的变异则归因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（Policy Implications）：本种子添加实验量化了25个引入至路边生境的按分类学分层的芸苔属（Brassica）分类群的表现变异。物种内嵌套的品种间的表现差异远大于物种间差异。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间变异。对于常规选育及转基因（genetically modified）物种而言，这一问题尤为突出——这类物种可能包含与物种评估层级下风险不同的分类群。因此，应考虑对未经过评估的植物亚种及品种开展与物种级风险评估类似的评估工作。