Department of Integrative Biology, University of Guelph, Guelph, ON, N1G 2W1, Canada.
Oecologia. 2012 Dec;170(4):1123-32. doi: 10.1007/s00442-012-2370-4. Epub 2012 Jun 6.
The global expansion of species beyond their ancestral ranges can derive from mechanisms that are trait-based (e.g., post-establishment evolved differences compared to home populations) or circumstantial (e.g., propagule pressure, with no trait-based differences). These mechanisms can be difficult to distinguish following establishment, but each makes unique predictions regarding trait similarity between ancestral ('home') and introduced ('away') populations. Here, we tested for trait-based population differences across four continents for the globally distributed grass Dactylis glomerata, to assess the possible role of trait evolution in its worldwide expansion. We used a common-environment glasshouse experiment to quantify trait differences among home and away populations, and the potential relevance of these differences for competitive interactions. Few significant trait differences were found among continents, suggesting minimal change during global expansion. All populations were polyploids, with similar foliar carbon:nitrogen ratios (a proxy for defense), chlorophyll content, and biomass. Emergence time and growth rate favored home populations, resulting in their competitive superiority over away populations. Small but significant trait differences among away populations suggest different introductory histories or local adaptive responses following establishment. In summary, the worldwide distribution of this species appears to have arisen from its pre-adapted traits promoting growth, and its repeated introduction with cultivation and intense propagule pressure. Global expansion can thus occur without substantial shifts in growth, reproduction, or defense. Rather than focusing strictly on the invader, invasion success may also derive from the traits found (or lacking) in the recipient community and from environmental context including human disturbance.
物种超越其祖先范围的全球扩张可以源自基于特征的机制（例如，与原种群相比，建立后进化的差异）或环境的机制（例如，繁殖体压力，没有基于特征的差异）。这些机制在建立后可能难以区分，但每种机制都对祖先（“本土”）和引入（“外来”）种群之间的特征相似性做出了独特的预测。在这里，我们测试了全球分布的草 Dactylis glomerata 在四大洲的基于特征的种群差异，以评估特征进化在其全球扩张中的可能作用。我们使用常见的温室实验来量化原种群和外来种群之间的特征差异，并评估这些差异对竞争相互作用的潜在相关性。发现各大洲之间的特征差异很小，这表明在全球扩张过程中几乎没有变化。所有种群都是多倍体，具有相似的叶片碳氮比（防御的代表）、叶绿素含量和生物量。出现时间和生长速度有利于本土种群，导致它们在与外来种群的竞争中具有优势。外来种群之间存在微小但显著的特征差异，这表明它们在建立后具有不同的介绍历史或局部适应反应。总之，该物种的全球分布似乎是由于其预先适应的特征促进了生长，以及其在栽培和强烈繁殖体压力下的重复引入。因此，全球扩张可能不会导致生长、繁殖或防御的重大转变。成功的入侵可能不仅源于入侵物种的特征（或缺乏），还可能源于受体群落中的特征以及包括人类干扰在内的环境背景。
