Data from: Herbivory enhances the resistance of mangrove forest to cordgrass invasion

The biotic resistance hypothesis proposes that biotic interactions, such as competition and herbivory, resist the establishment and spread of non-native species. The relative and interactive role of competition and herbivory in resisting plant invasions, however, remains poorly understood. We investigated the interactive role of competition and herbivory (by the native rodent Rattus losea) in resisting Spartina alterniflora (cordgrass) invasions into mangrove forests. In southern China, although exotic cordgrass numerically dominates intertidal mudflats and open gaps in mangrove forests, intact forests appear to be highly resistant to cordgrass invasion. A field transplant and rodent exclusion experiment showed that while the impact of rodent grazing on cordgrass was weak on mangrove forest edges and open mudflats, rodent grazing strongly suppressed cordgrass in mangrove understory habitats. A greenhouse experiment confirmed a synergistic interaction between grazing and light availability (a proxy for mangrove shading/competition) in suppressing cordgrass establishment, with the strongest impacts of grazing in low light conditions that likely weakened cordgrass to survive and resprout. When both were present, as in mangrove understory habitats, grazing and low light acted in concert to eliminate cordgrass establishment, resulting in resistance of mangrove forests to cordgrass invasion. Our results reveal that grazing by native herbivores can enhance the resistance of mangrove forests to cordgrass invasion in southern China, and suggest that investigating multifactor interactions may be critical to understanding community resistance to exotic invasions.生物抵抗假说（biotic resistance hypothesis）提出，种间竞争（competition）、植食作用（herbivory）等生物交互作用可抵御外来物种（non-native species）的定殖与扩散。然而，竞争与植食作用在抵御植物入侵过程中的相对作用及交互效应，目前仍有待深入阐明。本研究针对本土啮齿类黄毛鼠（Rattus losea）介导的植食作用与种间竞争的交互效应，探究其对红树林（mangrove forests）抵御互花米草（Spartina alterniflora，cordgrass）入侵的调控作用。在中国南方地区，尽管外来互花米草在潮间带泥滩（intertidal mudflats）及红树林林隙中占据数量优势，但完整的红树林生态系统似乎对互花米草入侵具有极强的抵抗能力。野外移植与啮齿动物排除实验（field transplant and rodent exclusion experiment）结果显示，尽管啮齿动物的啃食对红树林林缘及开放泥滩中的互花米草影响微弱，但在红树林林下生境中，啮齿动物啃食可显著抑制互花米草的生长。温室实验（greenhouse experiment）进一步证实，植食作用与光照可用性（light availability，可作为红树林遮阴/种间竞争的替代指标）之间存在协同交互效应（synergistic interaction），可共同抑制互花米草的定殖：在低光照条件下，啃食的抑制效应最强，这可能会削弱互花米草的存活与重新萌发能力。当两种因子共同存在时，如红树林林下生境，啃食与低光照可协同阻断互花米草的定殖，最终使红树林获得对互花米草入侵的抵抗能力。本研究结果表明，本土植食动物的啃食作用可增强中国南方红树林对互花米草入侵的抵抗能力，同时提示，探究多因子交互作用（multifactor interactions）或许是理解群落抵御外来物种入侵机制的关键所在。