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Title: Opposite effects of nutrient enrichment and an invasive snail on the growth of invasive and native macrophytes.
Author: Yan Y, Oduor AMO, Li F, Xie Y, Liu Y.
Journal: Ecol Appl; 2024 Jan; 34(1):e2737. PubMed ID: 36104847.
Abstract:
Many ecosystems are now co-invaded by alien plant and herbivore species. The evolutionary naivety of native plants to alien herbivores can make the plants more susceptible to the detrimental effects of herbivory than co-occurring invasive plants, in accordance with the apparent competition hypothesis. Moreover, the invasional meltdown hypothesis predicts that in multiply invaded ecosystems, invasive species can facilitate each other's impacts on native communities. Although there is growing empirical support for these hypotheses, facilitative interactions between invasive plants and herbivores remain underexplored in aquatic ecosystems. Many freshwater ecosystems are co-invaded by aquatic macrophytes and mollusks and simultaneously experience nutrient enrichment. However, the interactive effects of these ecological processes on native macrophyte communities remain an underexplored area. To test these effects, we performed a freshwater mesocosm experiment in which we grew a synthetic native community of three macrophyte species under two levels of invasion by an alien macrophyte Myriophyllum aquaticum (invasion vs. no invasion) and fully crossed with two levels of nutrient enrichment (enrichment vs. no enrichment) and herbivory by an invasive snail Pomacea canaliculata (herbivory vs. no herbivory). In line with the invasional meltdown and apparent competition hypotheses, we found that the proportional aboveground biomass yield of the invasive macrophyte, relative to that of the native macrophyte community, was significantly greater in the presence of the invasive herbivore. Evidence of a reciprocal facilitative effect of the invasive macrophyte on the invasive herbivore is provided by results showing that the herbivore produced greater egg biomass in the presence versus in the absence of M. aquaticum. However, nutrient enrichment reduced the mean proportional aboveground biomass yield of the invasive macrophyte. Our results suggested that herbivory by invader P. canaliculata may enhance the invasiveness of M. aquaticum. However, nutrient enrichment of habitats that already harbor M. aquaticum may slow down the invasive spread of the macrophyte. Broadly, our study underscores the significance of considering several factors and their interactions when assessing the impact of invasive species, especially considering that many habitats experience co-invasion by plants and herbivores and simultaneously undergo various other disturbances, including nutrient enrichment. 许多生态系统正经历着外来植物与外来食草动物的共同入侵。根据似然竞争假说, 与外来入侵植物相比, 因缺乏长期协同进化历史导致的本地植物的天真性 (naivety) 使其更容易受到外来食草动物入侵的负面影响。此外, 入侵崩溃假说预测: 在多物种入侵的生态系统中, 入侵物种能够互相加剧彼此对本地群落的负面影响。尽管越来越多的实验证据支持这些假说, 但水生生态系统中外来植物与外来食草动物如何相互促进其入侵仍未得到充分探索。尽管许多淡水生态系统正同时经历着富营养化、外来水生植物与外来食草动物的入侵, 但这些生态过程如何相互作用影响本地大型水生植物群落仍不明确。为了验证该问题, 本研究设置了一个淡水生态系统的中宇宙实验。实验为三因子两水平全因子设计, 即对由三种大型水生植物组成的本地群落施加外来植物粉绿狐尾藻 (Myriophyllum aquaticum)入侵(入侵vs不入侵)、富营养化(养分富集vs不富集)与外来入侵动物福寿螺 (Pomacea canaliculata)取食(取食vs不取食)处理。研究发现:与似然竞争假说和入侵崩溃假说的预测一致, 福寿螺显著提高了粉绿狐尾藻在群落中的生物量占比; 与未被粉绿狐尾藻入侵的本地群落相比, 福寿螺在被粉绿狐尾藻入侵的群落中具有更高的产卵量; 然而, 养分富集降低了粉绿狐尾藻在群落中的生物量占比。该研究表明: 外来入侵动物福寿螺的取食能够增强外来植物粉绿狐尾藻在群落中的入侵性; 但是, 水体富营养化可能减缓外来植物粉绿狐尾藻在其入侵生境的扩散。从广义上讲, 该研究强调在评估入侵物种的影响时, 需同时考虑到多个因素及其相互作用的重要性, 特别针对是那些正经历着外来植物与外来食草动物共同入侵, 且同时存在其他扰动因素(如富营养化)的生境。.

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