Plant–animal interactions fall within a mutualism–antagonism continuum, exerting a wide range of effects on plant reproductive success. These effects become even more complex and diverse when several disparate animal species interact with the same plant species. Despite the increasing number of studies about the influence of herbivory on plant performance, the outcomes mediated by pollination and the combined impact of multiple herbivores on pollination-specialized plants are underexplored. In this study, we chose the Mediterranean dwarf palm Chamaerops humilis (Arecaceae) to illustrate the isolated and joint effect of two contrasting introduced herbivores, the palm borer Paysandisia archon (Lepidoptera, Castniidae) and feral goats, on pollinator abundance and plant reproductive success. To this aim, we monitored moth herbivory and goat herbivory in four palm populations in Mallorca (Balearic Islands) during 2019 and 2020. The effect of herbivory varied widely depending on both the herbivore and the pollinator species. Moth herbivory had a positive effect on pollinator abundance and fruit initiation, whereas goat herbivory had a negative effect on inflorescence production, pollinator abundance and fruit initiation. In addition, both herbivores exerted unexpected nonadditive effects on palm reproduction. Palms attacked by both herbivore species produced many more inflorescences (up to 18-fold) but had a lower fruit initiation success (close to zero) than unattacked palms or those attacked by a single herbivore species. Interestingly, only one of the two main pollinator species (the nitidulid beetle Meligethinus pallidulus) was impacted by herbivory. Our study highlights the need to investigate the possible nonadditive effects of all coexisting herbivores on plant performance, especially when establishing conservation plans and pest control strategies.

中文翻译：

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两种截然不同的引进食草动物对专门授粉棕榈树繁殖的非累加效应

植物-动物相互作用属于共生-对抗连续体，对植物繁殖成功产生广泛影响。当几种不同的动物物种与同一植物物种相互作用时，这些影响变得更加复杂和多样化。尽管关于食草动物对植物性能影响的研究越来越多，但授粉介导的结果以及多种食草动物对授粉特化植物的综合影响仍未得到充分探索。在这项研究中，我们选择了地中海矮棕榈Chamaerops humilis（槟榔科）来说明两种截然不同的引进食草动物（棕榈蛀虫Paysandisia archon ）的孤立和联合效应（鳞翅目，Castniidae）和野山羊，关于传粉者丰度和植物繁殖成功率。为此，我们在 2019 年和 2020 年监测了马略卡岛（巴利阿里群岛）四个棕榈树种群的蛾食草动物和山羊食草动物。食草动物的影响因食草动物和传粉昆虫的种类而异。蛾类食草对传粉者丰度和果实萌生有积极影响，而山羊食草性对花序产生、传粉者丰度和果实萌生有负面影响。此外，两种食草动物都对手掌繁殖产生了意想不到的非加性效应。与未受攻击的棕榈树或受单一食草动物物种攻击的棕榈树相比，受到两种食草动物物种攻击的棕榈树产生了更多的花序（高达 18 倍），但果实启动成功率较低（接近于零）。有趣的是，Meligethinus pallidulus ) 受到食草动物的影响。我们的研究强调需要调查所有共存的食草动物对植物性能可能产生的非累加效应，尤其是在制定保护计划和害虫控制策略时。