Data from: Stronger effect of gastropods than rodents on seedling establishment, irrespective of exotic or native plant species origin

Experimental evidence about how generalist consumers affect exotic plant invasions is equivocal, but most tests have been limited to few plant species, single herbivore guilds, and single locations. Using a seed-addition experiment, we studied effects of gastropods and rodents on recruitment success of 37 exotic and 37 native plant species affiliated to three different functional groups (i.e. grasses, legumes and no-legume herbs). We replicated our seed addition x herbivore exclusion experiment at multiple grassland sites, located within a few km of each other in two regions, coastal Central California (USA) and southern Saxony-Anhalt (Germany). The two study regions differed in climate, land-use, invasion history and species pools which allowed us to disentangle general from context-specific effects. In both regions, herbivory by gastropods had a stronger impact on the proportion of recruited seedlings and the proportion of recruited species than rodent herbivory, but this effect was much more pronounced in California than in Germany. Especially, seedling recruitment of non-legume herbs and legumes suffered from gastropod herbivory. Contrastingly, the effect of rodents was negative at the German sites and positive at the Californian sites, likely driven by context-specific differences in the rodent assemblages. Across both study regions, exotics had higher seedling recruitment than natives, indicating that higher recruitment success constitutes an inherent feature of exotic species. After two years, more exotic than native species established at grassland sites in California while the opposite was true for the German grassland sites. Consistently across regions, native and exotic species did, however, not differ in their response to herbivory, suggesting that generalist consumers suppress recruitment and colonization of plant species irrespective of their origin. Our results demonstrate the importance of a multi-species, multi-site approach to separate general responses of exotic and native plants to generalist herbivory from local, regional or species-specific peculiarities.关于广食性消费者（generalist consumers）如何影响外来植物入侵的实验证据尚无定论，但绝大多数相关测试仅局限于少数植物物种、单一草食动物类群（herbivore guilds）以及单一研究地点。本研究借助种子添加实验（seed-addition experiment），探讨了腹足类（gastropods）与啮齿类（rodents）对隶属于3个不同功能群的37种外来植物与37种本土植物的招募成功率的影响，这3个功能群分别为禾草类、豆科类与非豆科草本类。我们在两个区域内的多个草原样地中重复开展了种子添加×草食动物排除实验，每个区域内的样地彼此相距仅数公里，两个区域分别为美国加利福尼亚中部沿海地区（coastal Central California (USA)）与德国萨克森-安哈尔特州南部（southern Saxony-Anhalt (Germany)）。 两个研究区域在气候、土地利用方式、入侵历史以及物种库（species pools）上均存在显著差异，这使得我们能够厘清通用效应与特定环境特异性效应之间的区别。在两个区域中，腹足类的草食作用对幼苗招募比例以及招募物种比例的影响均强于啮齿类，但该效应在加利福尼亚州远较德国更为显著。其中，非豆科草本植物与豆科植物的幼苗招募尤其容易受到腹足类草食作用的抑制。与之形成对比的是，啮齿类的草食作用在德国样地表现为负效应，而在加利福尼亚样地则表现为正效应，这一现象很可能由啮齿类群落组成的环境特异性差异所驱动。 综合两个研究区域的整体结果来看，外来物种的幼苗招募成功率均高于本土物种，这表明更高的招募成功率是外来植物的固有特征。实验开展两年后，加利福尼亚州的草原样地中成功定植的外来物种数量多于本土物种，而德国草原样地则呈现出相反的结果。不过，在两个区域中，本土与外来物种对草食作用的响应并无显著差异，这说明广食性消费者会抑制植物物种的招募与定植，且该抑制作用与植物的来源无关。 本研究结果证实，采用多物种、多样地的研究方法，能够有效区分外来与本土植物对广食性草食动物的通用响应，以及局部、区域或物种特异性的特有特征。