REU: Productivity, Plant Biomass, and Trophic Interactions Rivers

一个对所有食物网理论都有普遍兴趣的争论已经出现，即捕食者的攻击率是否应该取决于瞬时猎物密度，还是取决于猎物数量与共享它们的捕食者数量的比例。将攻击率按比例缩放到绝对猎物密度的模型预测，营养水平将随着生产力的提高而逐步增加，并且在食物链中添加环节之前，消费者和资源的生物量应该是不相关的。比率依赖模型预测，随着生产力的提高，所有营养水平的生物量都将持续单调增长，因此，消费者和资源的丰度应呈正协变。这些假设和预测可以用相当简单的实地观察来验证。P.I.建议在河流中使用实验和多河流比较的混合方法来检验两种模型的假设和预测。研究者将研究生产力对季节性河流食物网结构的影响，在冬季洪水之后，群落发展发生在可预测的夏季低流量季节，并通过遮蔽河流通道和施肥营养扩散物质（粘土罐）来控制初级生产力。在这些实验领域，P.I.将观察不同生产力制度下洪水后食物网的集合，记录生产者、主要消费者和捕食者行会的个体和生物量的累积；这些行会的分类组成、多样性及其组成种群的大小结构。P.I.将进行其他短期行为实验，以测量在不同的猎物和捕食者密度下，以及在有无植物覆盖的情况下，捕食优势猎物的普通捕食者的攻击率。为了测试主要研究地点实验结果的普遍性，研究者将调查几条代表环境生产力梯度的河流，并检查在夏季低流量季节和冬季洪水之后聚集的食物网的营养结构。

A debate of general interest to all food web theory has arisen over whether attack rates of predators should depend on instantaneous prey densities, or instead on ratios of prey numbers to the numbers of predators sharing them. Models with attack rates scaled to absolute prey densities predict that trophic levels will be added stepwise with increasing productivity, and that until links are added to food chains, biomass of consumers and resources should be uncorrelated. Ratio-dependent models predict continuous monotonic increases of biomass at all trophic levels with increasing productivity, so that abundance of consumers and resources should covary positively. These assumptions and predictions can be tested with fairly simple field observations. The P.I. proposes to test assumptions and predictions of both models in rivers using a mixture of experimental and multi-river comparisons. The investigator will study effects of productivity on food web structure in a seasonal river where, following winter floods, community development occurs during the predictable summer low- flow season and manipulate primary productivity by shading instream channels, and by fertilizing nutrient-diffusing substance (clay pots). In these experimental arenas, the P.I. will observe the post-flood assembly of food webs under various productivity regimes, recording the accrual of individuals and biomass in producer, primary consumer, and predator guilds; the taxonomic composition and diversity of these guilds, and the size structures of their component populations. The P.I. will conduct other, short-term behavioral experiments to measure attack rates of common predators feeding on dominant prey under different prey and predator densities, and in the presence and absence of plant cover. To test the generality of results from experiments at the primary study site, the investigator will survey several rivers that represent a gradient of environmental productivity, and examine trophic structures of food webs that assemble during the summer low-flow season, following winter floods.