Patterns, Controls, and Ecosytem Consequences of Trophic Structure in a Stream

本项目将描述荒漠河流生态系统营养结构的时空格局和总生物量在初级生产者、初级消费者和次级消费者营养水平上的比例。这一描述的空间背景将是斑块的分层排列，从相对较小规模的藻类或大型植物组合到大规模的流水-溪流-池塘栖息地。将沿着与洪水和干旱有关的连续轨迹评估时间变化。将在斑块内部和斑块之间评估每个营养级的生物量损失和收益，以确定斑块之间的联系。实验将确定形成营养结构的机制，并引起观察到的营养结构的时间变化。mesocosmos实验将在3级系统中操纵资源和消费者，而自然流实验将操纵营养物质和顶级捕食者。描述和实验结果将用于评估特定营养配置的生态系统水平后果；这一评价将表明群落属性的变化是否会驱动生态系统结构和功能的变化。本研究探讨了在确定自然界中观察到的模式时，自上而下（从食物链的顶部传播到底部）和自下而上（从底部传播）过程的相对影响。这些都是与生态系统对干扰的反应有关的重要问题。这项研究的设施非常好；研究人员是溪流生态学领域富有成效和创新精神的专家。

This project will describe the spatial and temporal patterns of trophic structure and the proportion of total biomass in primary producer, primary consumer, and secondary consumer trophic levels in a desert stream ecosystem. The spatial context for this description will be a hierarchical arrangement of patches from the relatively small scale of algal or macrophyte assemblages to large scale run-riffle-pool habitats. Temporal change will be assessed along successional trajectories associated with flooding and drying. Losses and gains of biomass at each trophic level will be evaluated both within and between patches to determine how patches are linked. Experiments will identify mechanisms shaping trophic structure and causing observed temporal changes in trophic structure. Mesocosm experiments will manipulate resources and consumers in 3-level systems, and a natural stream experiment will manipulate nutrients and top predators. Descriptive and experimental results will be used to evaluate ecosystem-level consequences of specific trophic configurations; this evaluation will indicate whether change in community-level properties drives change in ecosystem structure and function. This research explores questions concerned with the relative influence of top-down (propagated from the top to the bottom of the food chain) and bottom-up (propagated from the base) processes in determining patterns observed in nature. These are important issues concerned with the responses of ecological systems to disturbance. The facilities for this research are excellent; the investigators are productive and innovative experts in the area of stream ecology.