Data from: In the presence of specialist root and shoot herbivory, invasive-range Brassica nigra populations have stronger competitive effects than native-range populations

1. The evolution of increased competitive ability (EICA) hypothesis predicts that release from specialist herbivores enables invasive plants to evolve increased growth. The most powerful tests of EICA hypothesis are provided by approaches that simultaneously assess the effects of specialist herbivory and competitive interactions. However, such approaches are extremely rare, and hence how simultaneous release from root and shoot herbivory influence competitive ability of invasive plants remains little understood. 2. Here, we tested whether invasive-range Brassica nigra plants have evolved increased competitive ability, and whether expression of competitive ability depends on separate and simultaneous effects of specialist root and shoot herbivory. To do this, we grew B. nigra plants from eight invasive-range and eight native-range populations in the presence versus absence of competition with a community of native plant species, and in the absence versus presence of separate and simultaneous damage by a specialist root herbivore (Delia radicum) and a specialist shoot herbivore (Plutella xylostella). Brassica nigra performance was assessed by measuring biomass production and flowering of individual B. nigra plants. 3. In partial support of the EICA hypothesis, invasive-range B. nigra had greater flowering than native-range conspecifics in the absence of competition. However, contrary to a prediction of the EICA hypothesis, invasive-range B. nigra produced less aboveground biomass than native-range B.nigra in the absence of shoot herbivory and competition. Moreover, with simultaneous root and shoot herbivory, invasive-range B. nigra suppressed a competing community more strongly than native-range B. nigra did.
4. Synthesis: Our results suggest that invasiveness may be driven by mechanisms other than increased individual size. Simultaneous root and shoot herbivory in the invasive range may enhance suppressive effects of introduced plant species that have not completely escaped herbivore damage in the introduced range.

1. 竞争能力增强演化（Evolution of Increased Competitive Ability，EICA）假说预测，入侵植物在逃逸专食性植食动物的为害后，会演化出更强的生长能力。对该假说最有力的检验，来自于同时评估专食性植食为害与种间竞争交互效应的研究方法。然而这类研究方法极为罕见，因此学界对入侵植物同时脱离地下与地上植食为害后，其竞争能力会如何变化仍知之甚少。
2. 本研究旨在检验入侵分布区的黑芥（Brassica nigra）是否已演化出更强的竞争能力，以及其竞争能力的表达是否受专食性地下与地上植食为害的单独及同时施加效应的调控。为此，我们分别种植来自8个入侵分布区种群和8个原生分布区种群的黑芥植株，设置有/无本土植物群落竞争的处理，并设置无/有专食性地下植食动物萝卜蝇（Delia radicum）为害、无/有专食性地上植食动物小菜蛾（Plutella xylostella）为害，以及两者同时为害的处理。通过测定单株黑芥的生物量积累与开花情况，评估其生长表现。
3. 本研究结果部分支持EICA假说：在无竞争的条件下，入侵分布区黑芥的开花量高于原生分布区的同种植株。然而，与EICA假说的预测相悖，在无地上植食为害与竞争的条件下，入侵分布区黑芥的地上生物量低于原生分布区黑芥。此外，当同时受到地下与地上植食为害时，入侵分布区黑芥对竞争群落的抑制作用强于原生分布区黑芥。
4. 总结：本研究结果表明，植物的入侵性可能由个体体型增大以外的其他机制驱动。在入侵分布区中，同时受到地下与地上植食为害，可能会增强那些未完全逃逸植食为害的外来植物的群落抑制效应。