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. 进化增强竞争能力（Evolution of Increased Competitive Ability, EICA）假说预测，专食性草食动物的释放会使入侵植物演化出更强的生长能力。对该假说最具说服力的检验，来自同时评估专食性草食取食与种间竞争交互效应的研究路径。然而这类研究极为罕见，因此目前仍不清楚，同时脱离地下与地上草食动物的侵害，会如何影响入侵植物的竞争能力。
2. 本研究中，我们检验了入侵区黑芥（Brassica nigra）是否已演化出增强的竞争能力，以及其竞争能力的表达是否分别或同时受到专食性地下、地上草食动物的影响。为此，我们分别种植了来自8个入侵区种群与8个本土区种群的黑芥植株，设置了与本土植物群落共存或无竞争两种处理，同时设置了无专食性草食动物损伤、仅受专食性地下草食动物萝卜蝇（Delia radicum）取食、仅受专食性地上草食动物小菜蛾（Plutella xylostella）取食，以及同时受两者取食的四种损伤处理。我们通过测定单株黑芥的生物量积累与开花情况，来评估其生长表现。
3. 结果部分支持EICA假说：在无竞争条件下，入侵区黑芥的开花量高于本土区同种个体。但与EICA假说的预测相悖，在无地上草食动物取食且无竞争的条件下，入侵区黑芥的地上生物量低于本土区黑芥。此外，当同时受到地下与地上草食动物取食时，入侵区黑芥对竞争植物群落的抑制作用强于本土区黑芥。
4. 综合分析：我们的研究结果表明，植物的入侵性可能并非仅由个体体型增大驱动。在入侵区同时遭受地下与地上草食动物取食的情境下，或许会增强那些未完全脱离草食动物侵害的外来入侵植物的群落抑制效应。