The context-depency of biological invasions makes it difficult to understand why some species become succesfull invaders and others not. Such understanding requires studying closely-related invasive and non-invasive alien taxa sharing the same introduction history in the same environment. We identified this unusual situation in Kenya where the individuals that founded invasive Prosopis juliflora and non-invasive P. pallida populations are still present in original plantations. We evaluated field-measured traits, conducted glasshouse experiments simulating different nitrogen and water availability treatments, and did reciprocal transplants to compare functional traits and plasticity between the founders of both species (i.e. ‘invasive–non-invasive congeners' comparison), and between P. juliflora individuals from plantations and invaded sites (i.e. testing for rapid evolution during invasion). We found that planted individuals of P. julifora and P. pallida differed in a number of key traits related to performance and spread (root:shoot ratio, number of stems and susceptibility to seed damage) as well as in levels of phenotypic plasticity in growth responses to resource availability, which may explain their differential invasiveness. Offspring of invasive P. juliflora individuals had higher seed mass and production, germination, survival, produced more stems, matured earlier and had higher plasticity compared with those of founder individuals, indicative of rapid post-introduction evolution. By using this exceptional study system, we show that differences in values of only a few key traits, increased phenotypic plasticity and post-introduction evolution have all contributed to the success of P. juliflora as an invasive species in Kenya.

中文翻译：

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表型特征、它们的可塑性和快速进化对入侵成功的贡献：来自非凡自然实验的见解

生物入侵的背景依赖性使得难以理解为什么有些物种成为成功的入侵者而其他物种则不然。这种理解需要研究在同一环境中具有相同引入历史的密切相关的侵入性和非侵入性外来分类群。我们在肯尼亚发现了这种不寻常的情况，在该情况下，建立侵入性juliflora和非侵入性P. pallida种群的个体仍然存在于原始种植园中。我们评估了实地测量的性状，进行了模拟不同氮和水可用性处理的温室实验，并进行了相互移植以比较两个物种的创始人之间的功能性状和可塑性（即“侵入性-非侵入性同类物”比较），以及来自种植园和入侵地点的P. juliflora个体（即测试入侵期间的快速进化）。我们发现P. julifora和P. pallida 的种植个体在与性能和传播相关的许多关键性状（根：芽比、茎的数量和对种子损伤的易感性）以及生长表型可塑性水平方面存在差异对资源可用性的反应，这可以解释它们不同的侵入性。入侵P. juliflora 的后代与创始个体相比，个体具有更高的种子质量和产量、发芽、存活率、产生更多的茎、更早成熟且具有更高的可塑性，这表明引入后进化速度很快。通过使用这个特殊的研究系统，我们表明仅几个关键性状的价值差异、增加的表型可塑性和引入后的进化都有助于P. juliflora作为肯尼亚入侵物种的成功。