Biotic interactions and invasions by non-native plants

生物入侵是全球数十亿美元的问题，也是对生物多样性最严重的威胁之一，但预测它们是出了名的困难。生态学理论和最近的经验研究表明，植物与它们的天敌(食草动物和病原体)之间的相互作用可能在许多生物入侵中发挥关键作用。敌人释放假说(ERH)提出，非本土植物在新的地区定居时逃避天敌，提供了相对于本土植物的关键优势。竞争能力增强假说的进化(EICAH)表明，外来植物因此可以重新分配资源，从防御到生长和繁殖，增加它们取代本土植物的能力。生物抗性假说(BRH)提出，外来植物的侵袭性可以通过外来物种的竞争或捕食来降低。我们正在通过在原生和非原生地区的广泛植物上进行田间实验来检验这些假设。此外，我们正在使用豚草(Ambrosia Artemisiifolia)作为深入研究的模型。豚草是一种严重的农作物杂草和过敏原，原产于加拿大，但入侵欧洲。预测包括：P1：外来植物在入侵地区受到天敌的损害比本地(ERH)P2：外来植物受到天敌的损害比本地(ERH)小(ERH)P3：与敌人和竞争对手的负面互动将更大，与本地(ERH，BRH)，并将增加(对于敌人-ERH)或减少(对于竞争对手-EICAH)在新的地区P4：较低的敌人和竞争对手的影响导致更大的适应性，种群增长，以及外来物种(ERH，BRH，EICAH)的侵入性。迄今为止，很少有人对入侵理论进行这样的实验测试，也很少有人关注加拿大的生态系统。结果可能会为管理这一严重问题提供策略。

Biological invasions are a multi-billion dollar problem worldwide, and one of the most serious threats to biodiversity, but predicting them has proven notoriously difficult. Ecological theory and recent empirical studies suggest interactions between plants and their natural enemies (herbivores and pathogens) may play a key role in many biological invasions. The Enemy Release Hypothesis (ERH) proposes that non-native plants escape their natural enemies when colonizing new regions, providing a critical advantage over native plants. The Evolution of Increased Competitive Ability Hypothesis (EICAH) suggests exotic plants therefore can reallocate resources from defence to growth and reproduction, increasing their ability to displace natives. The Biotic Resistance Hypothesis (BRH) proposes that the invasiveness of exotic plants may be reduced by competition or predation by species native to the invaded area. We are testing these hypotheses with field experiments on a broad set of plants in both their native and non-native regions. As well, we are using ragweed (Ambrosia artemisiifolia), a serious crop weed and allergen native in Canada but invasive in Europe, as a model for intensive study. Predictions include: P1: Exotic plants suffer less damage by natural enemies in invaded areas than in native areas (ERH) P2: Exotic plants suffer less damage by natural enemies than do natives (ERH) P3: Negative interactions with enemies and competitors will be greater for exotics more closely related to natives (ERH, BRH), and will increase (for enemies - ERH) or decrease (for competitors - EICAH) with time in new regions P4: Lower impacts of enemies and competitors result in greater fitness, population growth, and invasiveness of exotics (ERH, BRH, EICAH). Few such experimental tests of invasion theory yet have been undertaken, and fewer have focussed on Canadian ecosystems. Results may suggest strategies for management of this serious problem.