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，但预测它们已被证明是非常困难的。生态学理论和最近的实证研究表明，植物与其天敌（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起着关键作用。敌人释放假说（ERH）提出，非本地植物在殖民新的地区时会逃避天敌，提供了比本地植物更重要的优势。竞争能力增强进化假说（EICAH）认为，外来植物因此可以将资源从防御重新分配到生长和繁殖上，从而增强它们取代本地植物的能力。生物抗性假说（BRH）认为，外来植物的入侵性可能会由于入侵地的本地物种的竞争或捕食而降低。我们正在测试这些假设与广泛的植物在其原生和非原生地区的实地实验。此外，我们正在使用豚草（Ambrosia artemisiifolia）作为深入研究的模型，豚草是一种严重的作物杂草和过敏原，原产于加拿大，但在欧洲具有入侵性。预测包括：第一名：外来植物在入侵区受到的天敌危害小于本地植物（ERH）P2：外来植物受到的天敌危害小于本地植物（ERH）P3：外来植物与天敌和竞争对手的负相互作用对于与本地植物关系更密切的外来植物来说会更大（ERH，BRH），并将增加（对于敌人- ERH）或减少（对于竞争对手- EICAH）在新地区的时间P4：较低的影响的敌人和竞争对手的结果更大的健身，人口增长，和外来入侵（ERH，BRH，EICAH）。很少有这样的入侵理论的实验测试尚未进行，更少有集中在加拿大的生态系统。研究结果可能会为这一严重问题的管理策略提出建议。

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.