Interactions between non-native plants and their natural enemies in core and marginal populations

非本土植物在加拿大南部是一个严重的环境和经济问题；然而，很少有植物延伸到北纬地区。非原住民的北方活动范围可能直接受到寒冷气候的影响，但也可能受到与天敌(食草动物和病原体)相互作用的积极和消极影响。北方种群可能会通过逃避敌人而获得优势，这些敌人本身无法分散到北方地区或在那里生存；另一方面，生长缓慢的北方植物可能难以补充它们未能逃脱的任何敌人失去的组织，从而降低它们的成功。 在这项研究中，我将调查与天敌的相互作用是否有助于限制非本土植物的分布；我还将把这些结果与本土物种的影响进行比较，看看本土和外来物种是否受到不同因素的限制。我将在安大略省从五大湖到哈德逊湾低地的纬度梯度上进行实地试验和调查。在每个地点，我将测量食草动物和病原体造成的破坏的影响，以检验五个假设： 非本土植物在没有辅助的情况下无法在当前北方边界以外生存； H2：外来植物的边缘种群比内部种群更少受到天敌的攻击； H3：外来细菌在边缘地区的土壤中不如内陆地区的土壤明显； H4：外来物种边缘种群与内部种群对食草动物的耐受性降低； H5：竞争和食草性对外来物种边缘种群和内部种群性能的净影响不同。 结果将决定我们是否能够提高我们预测和管理外来物种进一步传播的能力，提供有关它们的敌人和竞争对手的信息。此外，了解边缘种群的过程将有助于预测入侵物种对未来气候变化的可能反应。

Non-native plants are a serious environmental and economic problem in southern Canada; however, few extend to northern latitudes. The northern range limits of non-natives may be set directly by cold climate, but also may be influenced both positively and negatively by interactions with natural enemies (herbivores and pathogens). Northern populations may gain an advantage by escaping enemies that are themselves unable to disperse to or survive in northern sites; on the other hand, slow-growing northern plants may have trouble replacing tissues lost to any enemies that they fail to escape, reducing their success. In this research, I will investigate whether interactions with natural enemies help to set limits to the distribution of non-native plants; I also will compare these results with effects on native species, to see if natives and exotics are limited by different factors. I will establish field experiments and surveys at Ontario sites along a latitudinal gradient from the Great Lakes to the Hudson Bay Lowlands. At each location, I will measure the effects of damage by herbivores and pathogens, to test five hypotheses: H1: Non-native plants are unable to survive unassisted beyond current northern limits; H2: Marginal populations of non-native plants are less attacked by natural enemies than interior populations; H3: Pathogens of exotics are less prominent in soils of marginal areas than soils of interior areas; H4: Tolerance of herbivory is reduced in marginal vs. interior populations of exotics; H5: Net effects of competition and herbivory on performance differ for marginal and interior populations of exotics. Results will determine if we can improve our ability to predict and manage further spread of exotics with information about their enemies and competitors. As well, understanding processes in marginal populations will help to predict likely responses of invasive species to future climate change.