Data from: Functional trait differences and trait plasticity mediate biotic resistance to potential plant invaders

1. Biotic resistance represents an important natural barrier to potential invaders throughout the world, yet the underlying mechanisms that drive such resistance are still debated. In theory, native communities should repel both functionally similar invaders which compete for the same resources, and invaders which possess less competitive traits. However, environmental stress, trade-offs across vital rates and competition-induced plastic trait shifts may modify expected competitive outcomes, thereby influencing invasion dynamics.
2. In order to test these theoretical links between trait distributions and biotic resistance, we performed a mesocosm experiment with 25 non-native ornamental species invading native plant communities. Each non-native species was grown with and without the native community under two watering treatments (regular and reduced). We measured biotic resistance as the difference in performance of non-native individuals grown with and without the community in terms of their survival, growth and reproduction. We quantified overall functional dissimilarity between non-native ornamental individuals and native communities based on the combination of plant height, specific leaf area and seed mass. Then, assuming each of these traits is also potentially linked to competitive ability, we measured the position of non-natives on trait hierarchies. While height is positively correlated with competitive ability for light interception, conservative leaf and seed characteristics provide greater tolerance to competition for other resources. Finally, we quantified plastic trait shifts of non-native individuals induced by competition.
3. Indeed, the native community repelled functionally similar individuals by lowering their survival rate. Simultaneously, shorter ornamental individuals with larger specific leaf areas were less tolerant to biotic resistance from the community across vital rates, although the effect of trait hierarchies often depended on watering conditions. Finally, non-natives responded to competition by shifting their traits. Most importantly, individuals with more competitive traits were able to overcome biotic resistance also through competition-induced plastic trait shifts.
4. Synthesis. Our results highlight that both functional dissimilarity and trait hierarchies mediate biotic resistance to ornamental plant invaders. Nevertheless, environmental stress as well as opposing trends across vital rates are also influential. Furthermore, plastic trait shifts can reinforce potential invaders’ competitive superiority, determining a positive feedback.

1. 生物抗性（biotic resistance）是全球范围内抵御潜在入侵物种的重要天然屏障，但其背后的驱动机制仍存在争议。理论上，本地群落应当能够排斥两类入侵物种：一类是功能与本地物种相似、会争夺相同资源的入侵者，另一类是竞争力较弱的入侵者。然而，环境压力、生命率间的权衡效应，以及竞争诱导的性状可塑性变化（plastic trait shifts），可能会改变预期的竞争结果，进而影响入侵动态。
2. 为验证性状分布与生物抗性之间的上述理论关联，我们开展了一项中型实验生态系统（mesocosm）实验，以25种外来观赏物种入侵本地植物群落。我们设置了两种浇水处理（正常供水与减少供水），将每种外来物种分别在有、无本地群落的条件下进行栽培。我们以外来个体在有、无本地群落时的生存、生长与繁殖表现差异来量化生物抗性。基于株高、比叶面积（specific leaf area）和种子质量（seed mass）三项性状的组合，我们量化了外来观赏个体与本地群落之间的整体功能差异。随后，假设上述每项性状均可能与竞争能力相关，我们测定了外来物种在性状层级（trait hierarchies）上的位置。尽管株高与光捕获相关的竞争能力呈正相关，但保守型叶片与种子特征则对其他资源的竞争具有更强的耐受能力。最后，我们量化了竞争诱导的外来个体性状可塑性变化。
3. 研究结果显示，本地群落通过降低功能相似个体的存活率来实现排斥。与此同时，株高较矮、比叶面积更大的观赏个体，在各项生命率维度上对本地群落产生的生物抗性的耐受能力更弱，尽管性状层级的影响通常取决于浇水条件。最后，外来物种会通过改变自身性状来响应竞争。最为关键的是，具备更强竞争性状的个体，还可通过竞争诱导的性状可塑性变化来克服生物抗性。
4. 综合分析。本研究结果表明，功能差异与性状层级共同介导了观赏植物入侵者面临的生物抗性。然而，环境压力以及生命率间的相反趋势同样具有重要影响。此外，性状可塑性变化可强化潜在入侵物种的竞争优势，形成正向反馈循环。