Omnivory and food chain length of aquatic food webs: Influence on trophic structure and contaminant dynamics

食物网提供了能量、营养和污染物在生物群落或生态系统内的路径和运动。简单地说，它们代表了谁吃了谁。动物在食物网中的位置，从初级生产者(即植物)到顶级捕食者(如北极熊)，对动物的生物学和生态特征及其对人类行动的脆弱性有重大影响。食物网是生态学的中心租户，是制定管理和保护计划的统一指标，但它是复杂的，在空间和时间上都是动态的。随着水生生态系统面临越来越大的压力，包括入侵物种、气候变化、污染和资源过度开发，迫切需要了解支撑食物网结构和功能的机制和过程。不幸的是，这是一项艰巨的任务，特别是在不易观察到的水生生态系统中。最近，化学示踪剂的发展提高了我们研究水生生态系统的能力，并为食物网提供了新的见解。这项研究的重点是量化食物网的两个至关重要的特征：杂食性和食物链长度。杂食性最常见的是以动物和植物为食，但它是生物体的一种更复杂的特征，反映了它们在不同的营养水平和/或不同的栖息地取食。食物链长度反映了生态系统中营养水平的数量，并对生态系统可以支持的动物数量有影响。杂食性动物被认为通过利用不同类型的食物为生态系统提供稳定性，但杂食性动物的流行率及其随食物链长度的变化仍未量化。这两个特征构成了食物链，并对多氯联苯和汞等污染物的积累产生了深远的影响，这些污染物进入鱼类和野生动物，最终进入人类。利用一系列化学示踪剂，包括胃内容物的稳定同位素和DNA，我将使用最先进的技术，如胃内容物的稳定同位素和DNA分析，对五大湖和北极海洋环境的水生生态系统中的杂食性动物、食物链长度和污染物进行量化。五大湖拥有北美80%的淡水，对加拿大的经济和社会福祉至关重要，支持大型商业和休闲渔业。北极是加拿大的优先事项，但这个未被充分研究的生物群面临着来自资源开发、航运和渔业增加以及气候变化的越来越大的压力。这两个生态系统都正在经历生态系统的变化，这使得管理具有挑战性，并难以预测污染物的暴露和影响。如果我们要有效地管理和保护这些重要的生态系统及其提供的服务，就需要通过专门的实地和实验室研究，更好地了解杂食性动物和食物链长度的重要性及其对污染物的影响。

Food webs provide the pathways and movement of energy, nutrients and contaminants within a biological community or ecosystem. In simple terms, they are representations of who eats whom. Where animals are positioned in food webs, from primary producers (i.e., plants) to top predators (e.g., polar bears), has a major impact on the animal's biological and ecological characteristics and their vulnerability to man's actions. Food webs are a central tenant of ecology and a unifying metric for developing management and conservation plans but are complex and spatially and temporally dynamic. With increasing stress on aquatic ecosystems, including invasive species, climate change, pollution and resource overexploitation, there is a pressing need to understand the mechanisms and processes that underpin the structure and function of food webs. Unfortunately, this is a difficult task, particularly in aquatic ecosystems that are not easily observed. Recently, the development of chemical tracers has improved our ability to study aquatic ecosystems and has provided new insights into food webs. This research proposal is focused on quantifying two critically important characteristics of food webs: omnivory and food chain length. Omnivory is most commonly associated with eating animals and plants but it is a more complex characteristic of organisms that reflects feeding on different trophic levels and/or from different habitats. Food chain length reflects the number of trophic levels in an ecosystem and has implications for the number of animals an ecosystem can support. Animals that are omnivores are believed to provide stability to ecosystems by utilizing different types of foods, but the prevalence of omnivory and how it varies with food chain length remains un-quantified. Both of these characteristics structure food webs and have a profound influence on the accumulation of contaminants, such as PCBs and mercury, into fish and wildlife and ultimately humans. Using a range of chemical tracers, including stable isotopes and DNA of stomach contents, I will quantify omnivory, food chain length and contaminants in aquatic ecosystems of the Great Lakes and Arctic marine environment using state-of-the-art techniques such as stable isotopes and DNA analysis of stomach contents. The Great Lakes hold >80% of North America's fresh water and are critical to Canada's economic and social well being, supporting large commercial and recreational fisheries. The Arctic is a priority for Canada but this understudied biome faces increasing pressure from resource development, increased shipping and fishing and climate change. Both of these ecosystems are experiencing ecosystem change making management challenging and predicting contaminant exposure and effects difficult. If we are to effectively manage and preserve these vital ecosystems and the services they provide, there is a need to better understand the importance of omnivory and food chain length, and their influence on contaminants, through dedicated field and laboratory studies.