Exchanges of enemies between native and non-native plants

正如敌人释放假说所描述的那样，逃避本土范围的天敌(食草动物和病原体)通常被认为增加了非本土植物的侵袭性。然而，一旦进入一个新的地区，外来入侵者就会获得从入侵的物种中招募的新敌人。此外，来自入侵者原始范围的敌人(包括生物控制剂)可能会意外或故意地被引入；这些物种也可能攻击当地的原住民。因此，很少有入侵者没有天敌，其中许多天敌是与共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，通过生物抵抗来减少他们的成功。此外，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人)和溢出(本地敌人传播到外来宿主，然后传播回原来的宿主)参与对本地人的反馈；这些反馈构成了入侵者生态影响的一个重要但未被开发的组成部分。然而，并不是所有的入侵种群都同样受到这种相互作用的影响。首先，远亲关系较远的原住民和外来者之间交换的可能性可能较低。其次，在空间上与敌人源头隔绝的植物可能会经历更少的交换。第三，敌人的数量可能会因地区不同而不同，这导致了交换的地理趋势。第四，即使敌人是共同的，对损害的容忍可能会在有利的栖息地减少他们的影响。最后，像食草动物这样的影响对于少数入侵者来说可能是最关键的；这是大多数不成功的入侵失败的阶段。 在这里，我建议调查影响原住民和外来者之间敌人交换的关键因素，以及对两者表现的影响。我们将通过实验测试系统发育、空间隔离和地理变异对共同敌人的重要性，将评估容忍在减轻这些影响方面的作用，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，这项新颖的研究将阐明共同敌人对外来物种传播的重要性及其对共生原住民的影响，并将有助于我理解入侵植物与其天敌之间的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.