Exchanges of enemies between native and non-native plants

逃离原生范围的天敌（食草动物和病原体）往往被认为是增加非原生植物的入侵性，如敌人释放假说所描述的。然而，一旦进入一个新的地区，外来入侵者就会从入侵范围内的物种中获得新的敌人。同时，来自入侵者原始范围的敌人（包括生物控制剂）可能是偶然或故意共同引入的;这些物种也可能攻击当地的土著人。因此，很少有入侵者是没有天敌的，其中许多是与共同发生的本土植物共享的。 共同的敌人可以对入侵者产生重大影响，通过生物抗性减少他们的成功。同样，共同的敌人可能通过溢出（引入的敌人从外来宿主传播到本地宿主）和溢出（本地敌人传播到外来宿主，然后传播回原始宿主）参与对本地宿主的反馈;这些反馈构成入侵者生态影响的重要组成部分，但未得到充分研究。然而，并非所有的入侵种群都受到这种相互作用的影响。首先，亲缘关系较远的本地人和外来人之间交换的可能性可能较低。第二，在空间上与敌人源隔离的植物可能会经历减少的交换。第三，敌人的数量可能因地区而异，从而导致交换的地理趋势。第四，即使敌人是共同的，对损害的容忍可能会减少它们在有利栖息地的影响。最后，如草食性的影响可能是最关键的小种群的入侵者，这是最不成功的入侵失败的阶段。 在这里，我建议调查的关键因素，影响本地人和外来物种之间的敌人的交流，以及两者的性能的后果。我们将通过实验测试共同敌人的遗传学，空间隔离和地理变异的重要性，将评估耐受性在减轻这些影响中的作用，并将调查影响小种群成功的因素。通过阐明入侵植物周围复杂的相互作用网络，这项新的研究将阐明共同的敌人对外来物种传播的重要性及其对共存本地物种的影响，并将有助于我了解入侵植物与其天敌之间相互作用的长期目标。

Escape from native-range natural enemies (herbivores and pathogens) often is argued to increase the invasiveness of non-native plants, as described by the Enemy Release Hypothesis. However, once in a new region, exotic invaders acquire new enemies recruited from invaded-range species. As well, enemies from the invader's original range (including biocontrol agents) may be accidentally or deliberately co-introduced; these species also may attack local natives. As a result, few invaders are free of natural enemies, many of which are shared with co-occurring native plants. Shared enemies can have significant impacts on invaders, reducing their success through biotic resistance. As well, shared enemies may participate in feedbacks on natives through spillover (spread of introduced enemies from exotic hosts to natives) and spillback (spread of native enemies to exotics followed by spread back onto their original hosts); these feedbacks constitute an important but underexplored component of invaders' ecological impacts. However, not all invasive populations may be equally affected by such interactions. First, the probability of exchange is likely to be lower between more distantly-related natives and exotics. Second, plants that are spatially isolated from sources of enemies may experience reduced exchange. Third, populations of enemies may vary regionally, resulting in geographic trends in exchange. Fourth, even if enemies are shared, tolerance to damage may reduce their effects in favourable habitats. Finally, impacts such as herbivory are likely to be most critical for small populations of invaders; this is the stage at which most unsuccessful invasions fail. Here, I propose to investigate key factors that affect the exchange of enemies between natives and exotics, and the consequences for the performance of both. We will experimentally test the importance of phylogeny, spatial isolation, and geographic variation for shared enemies, will evaluate the role of tolerance in mitigating these impacts, and will investigate factors affecting the success of small populations. By illuminating the complex web of interactions surrounding invasive plants, this novel research will clarify the importance of shared enemies to the spread of exotics and their impacts on co-occurring natives, and will contribute to my long-term objective of understanding interactions between invasive plants and their natural enemies.