Syndromes in suites of correlated traits suggest multiple mechanisms facilitating invasion in a plant range-expander

Various mechanisms can facilitate the success of plant invasions simultaneously, but may be difficult to disentangle. We compared plants of the range-expanding species Bunias orientalis from populations of native, invasive and exotic, not yet invasive origin in a field common garden over two years. Plants were grown under two nitrate-regimes and multiple traits regarding growth, defence, antagonist loads and reproduction were measured. We used a rank-based clustering approach to assign correlated traits to distinct suites. These suites were analysed for “syndromes” that are expressed as a function of population origin and/or fertilisation treatment and might represent different invasion mechanisms. Indeed, distinct suites of traits were differentially affected by these factors. Our results suggest that different pre-adaptation properties, such as certain growth characteristics and intraspecific chemical variation, as well as post-introduction adaptations to antagonists and resource availability in novel habitats are candidate mechanisms that facilitate the success of invasive B. orientalis in parallel. We conclude that rank-based clustering is a robust and expedient approach to integrate multiple traits for elucidating invasion syndromes within individual species. Studying a multitude of traits at different life-history and establishment stages of plants grown under distinct resource treatments reveals species-specific trade-offs and resource sinks and simplifies the interpretation of single trait functions for plant invasiveness.

多种机制可共同推动植物入侵的成功，但这些机制往往难以厘清彼此的相对贡献。本研究在为期两年的田间同质园试验（common garden）中，对来自原生境、入侵境以及外来未入侵境种群的分布区扩张物种疣果匙荠（Bunias orientalis）植株开展了比较分析。实验设置了两种硝酸盐供应水平，测定了植株的生长、防御、天敌负荷以及繁殖等多项性状。我们采用基于秩的聚类方法（rank-based clustering approach），将相关性状归为不同的性状组。针对这些性状组，我们分析了随种群起源或施肥处理表达的“性状综合征（syndromes）”，这类综合征或可代表不同的入侵机制。确实，不同的性状组会受到上述因素的差异化影响。研究结果表明，多种潜在机制可共同促进入侵性疣果匙荠的成功，包括不同的预适应特性（如特定的生长特征与种内化学变异），以及物种引入后对新生境中天敌压力与资源可利用性的适应性演化，这些均为潜在的入侵促进机制。综上，基于秩的聚类方法是一种稳健且高效的多性状整合手段，可用于阐明单一物种内部的入侵性状综合征。在不同资源处理条件下，针对植物不同生命史与建植阶段的多项性状展开研究，可揭示物种特有的性状权衡与资源库动态，同时简化单一性状功能对植物入侵性影响的解读。