Exploring ecological surprises by multiple stressors of aquatic food webs

我的研究计划的主要目标是发现水生食物网响应全球变化的生态驱动因素。定义全球变化的多种与人类有关的压力源往往对食物网产生复杂的非加性影响，因此，基于单一压力源已知影响的总和，这些影响无法轻易预测。因此，极端气候变化和其他压力因素经常产生令人震惊的“生态意外”。我已经开发了一个概念模型的生态机制，影响多营养反应的多种应激源。该模型基于三个操作假设：1)由于动物对快速环境变化的耐受性较差，压力源对顶级捕食者的协同作用比对植物的协同作用更明显；2)与顶级捕食者相比，耐受性较强的植物物种更容易在受到压力的生态系统中定居，并在功能上弥补已灭绝的物种；因此，3)在受到压力的生态系统中，顶级捕食者、食草动物和植物之间的耐受性差异导致它们之间的相互作用（例如，捕食和食草）发生了深刻的变化。我的研究小组通过在加拿大落基山脉的自然无鱼高山湖泊进行实验来验证这些假设，这些湖泊正日益受到极端气候事件、入侵物种引入和空气污染的影响。因此，这些高度敏感的物种贫乏生态系统是研究多种应激源对营养复杂性影响的绝佳场所。我们研究了整个食物网、单一营养群体的反应及其相互作用，通过将它们依次暴露于夏季加热事件和其他压力源，使用潜水温室中观系统。我们还研究了耐受性物种的扩散和定植作为缓冲高山食物网免受快速环境变化影响的一种手段的重要性。我通过比较高山湖泊中暴露在相同压力源组合下的实验和自然发生的食物网，来完善和升级我提出的模型。我们的发现将有助于更好地解释为什么我们应该期待未来全球变化的意外。

The main goal of my research program is to discover ecological drivers of aquatic food-web responses to global change. Multiple human-related stressors that define global change often exert complex non-additive effects on food webs, which cannot therefore be easily predicted based on the sum of known effects by single stressors. Consequently, extreme climate change together with other stressors often generate alarming "ecological surprises." I have developed a conceptual model of the ecological mechanisms affecting multi-trophic responses to multiple stressors. The model is based on three operating hypotheses: 1) stressors exert more pronounced synergistic impacts on top predators than on plants because animals are less tolerant of rapid environmental change, 2) tolerant plant species more than top predators are able to readily colonize stressed ecosystems and functionally compensate for extinct species, and thus, 3) differences in tolerances among top predators, herbivores, and plants result in their interactions (e.g., predation and herbivory) being profoundly altered in stressed ecosystems. My research group tests these hypotheses by conducting experiments in naturally fishless alpine lakes of the Canadian Rockies, which are being increasingly impacted by extreme climate events, introduced invasive species, and air pollution. Therefore, these highly sensitive species-poor ecosystems are excellent venues for investigating the effects of multiple stressors on trophic complexity. We examine the responses of whole food webs, single trophic groups and their interactions by exposing them sequentially to summer heating events and other stressors using submersible greenhouse mesocosms. We also examine the importance of dispersal and colonization by tolerant species as a means of buffering alpine food webs against the impacts of rapid environmental change. I refine and upgrade my proposed model through comparison of experimental and naturally occurring food webs in alpine lakes that are exposed to the same combination of stressors. Our findings will help better explain why we should expect the unexpected from future global change.