Biotic interactions and invasions by non-native plants

生物入侵是世界范围内一个数十亿美元的问题，也是对生物多样性最严重的威胁之一，但事实证明，预测它们是非常困难的。生态学理论和最近的实证研究表明，植物与其天敌（草食动物和病原体）之间的相互作用可能在许多生物入侵中起关键作用。敌人释放假说（ERH）提出，非本地植物在殖民新地区时可以逃离天敌，这对本地植物来说是一个关键的优势。增强竞争能力的进化假说（EICAH）认为外来植物因此可以重新分配资源，从防御到生长和繁殖，增加它们取代本地植物的能力。生物抗性假说（BRH）认为外来植物的入侵可能会被入侵地区的本地物种竞争或捕食而减少。我们正在对这些假设进行实地试验，在大量植物的原生和非原生地区进行试验。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，但入侵欧洲。预测包括：P1：外来植物在入侵地区受到的天敌伤害小于原生地区（ERH） P2：外来植物受到的天敌伤害小于原生地区（ERH） P3：与原生地区关系更密切的外来植物（ERH， BRH）与敌人和竞争对手的负相互作用将更大，并将随着时间的推移而增加（对于敌人- ERH）或减少（对于竞争对手- EICAH） P4。敌人和竞争者的影响较低导致更大的适应度，种群增长和外来物种入侵（ERH， BRH， EICAH）。迄今为止，很少有人对入侵理论进行这样的实验测试，而且很少有人关注加拿大的生态系统。结果可能为管理这一严重问题提供策略建议。

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.