Collaborative Research: Trophic Structure and the Stoichiometry of Nitrogen and Phosphorus in the Pelagic Food Web

生态学家越来越认识到，生态系统中能量和化学元素的储存和处理模式受到生态系统中存在的生态群落组成的强烈影响。在湖泊中，“顶级捕食者”（即以鱼为食的鱼类，如鲈鱼）的丰度可以对系统的各个层面产生强烈影响，包括植物生产者的丰度和生产力以及化学元素的循环。这是因为掠食性鱼类会吃掉以浮游生物为食的鱼类，比如小鱼，而这些鱼类反过来又会影响食草动物（浮游动物）。最后，浮游动物既能调节植物生产者（浮游植物）和分解者（细菌）的丰度，又能循环养分。本项目主要研究食物网结构对微生物生长所需营养元素（氮和磷）相对可用性的影响。它测试了最近发展起来的一种基于生理学的理论的预测，该理论旨在了解不同的浮游动物物种如何再生食物中存在的氮和磷。通过改变这些草食性浮游动物的动态，鱼类捕食可以影响氮和磷的循环。以加拿大的实验湖区为基地，主要的研究方法将包括在湖泊的大型围栏中对营养物质和浮游动物进行实验操作，以及对整个湖泊的食物网结构进行操作（通过向缺乏这种鱼类的两个湖泊引入梭子鱼）。这些研究对理解生态系统中控制元素循环的过程具有直接的应用价值；这些过程在直接社会的各个领域发挥着关键作用，包括全球气候变化、环境中污染物的动态和供水的退化。

Ecologists are increasingly realizing that patterns of storage and processing of energy and chemical elements in ecosystems are strongly influenced by the composition of the ecological communities present in the ecosystem. In lakes, the abundance of "top predators" (i.e. fish-eating fish species like bass) can have strong effects on all levels of the system, including the abundance and productivity of plant producers and the cycling of chemical elements. This occurs because predatory fish consume plankton-feeding fish, like minnows, which in turn influence herbivorous consumers (zooplankton). Finally, zooplankton both regulate the abundance of plant producers (phytoplankton) and decomposers (bacteria) and recycle nutrients. This project focusses on the effects of food web structure on the relative availability of nutrient elements critical for microbial growth (nitrogen and phosphorus). It tests the predictions of a recently-developed, physiologically-based theory designed to understand how different zooplankton species regenerate nitrogen and phosphorus present in their food. By altering the dynamics of these herbivorous zooplankton, fish predation can therefore influence the cycling of nitrogen and phosphorus. Based at the Experimental Lakes Area in Canada, the main research approaches will in involve experimental manipulations of nutrients and zooplankton in large enclosures in lakes as well as whole-lake manipulations of food-web structure (via introduction of pike to two lakes which lack such a fish-eating species). THese studies have direct application to understanding the processes controlling elemental cycling in ecosystems; such processes play a critical role in various areas of direct societal, including global climate change, the dynamics of contaminants in the environment, and degradation of water supplies.