Neighbor tolerance, not suppression, provides competitive advantage to non-native plants

High competitive ability has often been invoked as a key determinant of invasion success and ecological impacts of non-native plants. Yet our understanding of the strategies that non-natives use to gain competitive dominance remains limited. Particularly, it is unknown whether the two non-mutually exclusive competitive strategies, neighbor suppression and neighbor tolerance, are equally important for the competitive advantage of non-native plants. Here, we analyze data from 192 peer-reviewed studies on pairwise plant competition within a Bayesian multilevel meta-analytic framework and show that non-native plants outperform their native counterparts due to high tolerance of competition, as opposed to strong suppressive ability. Competitive tolerance ability of non-native plants was driven by neighbor's origin and was expressed in response to a heterospecific native but not heterospecific non-native neighbor. In contrast to natives, non-native species were not more suppressed by hetero- vs. conspecific neighbors, which was partially due to higher intensity of intraspecific competition among non-natives. Heterogeneity in the data was primarily associated with methodological differences among studies and not with phylogenetic relatedness among species. Altogether, our synthesis demonstrates that non-native plants are competitively distinct from native plants and challenges the common notion that neighbor suppression is the primary strategy for plant invasion success.

竞争能力常被视为非本土植物（non-native plants）入侵成功及其生态影响的关键决定因素。然而，学界对非本土植物借以获得竞争优势的策略仍知之甚少。具体而言，尚不明确两种非互斥的竞争策略——邻体抑制（neighbor suppression）与邻体耐受（neighbor tolerance）——是否对非本土植物的竞争优势同等重要。本研究基于贝叶斯多层元分析框架（Bayesian multilevel meta-analytic framework），对192项有关植物成对竞争的同行评议研究数据展开分析，结果表明非本土植物相较于本土同类植物表现更优，其原因在于较强的竞争耐受能力，而非突出的抑制能力。非本土植物的竞争耐受能力受邻体起源所驱动，仅在面对异种本土邻体时表现出耐受能力，而对异种非本土邻体则无此响应。与本土植物不同，非本土植物并未因异种邻体而比同种邻体受到更强的抑制，这一现象部分源于非本土植物种群内的种内竞争（intraspecific competition）强度更高。研究数据的异质性主要源于各研究间的方法学差异，而非物种间的系统发育亲缘关系。综上，本综合分析表明，非本土植物在竞争特性上与本土植物存在显著差异，并对“邻体抑制是植物入侵成功的核心策略”这一主流观点提出了挑战。