Collaborative Research: Community Mechanisms for Ecosystem Variability in Castle Lake, California.

这项建议旨在评估在一系列全湖食物网操作期间，群落相互作用(捕食、竞争)如何产生生态系统动态的变化。这项拟议的工作利用了一个由国家科学基金会LTREB拨款资助的鱼类放养操作计划，以及在该地点收集数据的长期记录。对食物网主要组成部分的资源和捕食者关系的详细研究将使研究人员能够了解导致每个热带水平并最终在生态系统本身发生变化的机制。将通过声学和视频观察以及更传统的渔业技术监测鱼类种群，并随着外部鱼类放养强度的重大变化而评估浮游动物的丰度、生长、摄食、补充和程度的变化。还将使用浮游动物种群生物学技术(卵比例、出生和死亡率估计)以及食物状况的生理指标(脂肪含量)来检查浮游动物动态(特别是水蚤)的变化。PI‘s还将评估鲑鱼浮游活动在多大程度上解释了观察到的水蚤死亡。将通过测量浮游动物在主要藻类群上的捕食率，并确定就地藻类动态的变化是否可归因于放牧影响，来评估浮游植物与捕食者的关系。将通过监测藻类营养状况和使用稀释生物测定来确定主要限制营养物质的特定物种生长动力学，来评估浮游植物与资源的关系。此外，将使用15N同位素技术评估外部供应的N与内部供应的N(即在食物网内)在支持藻类生产力方面的作用。浮游生物和营养/食物供应在改变浮游生物动态方面的作用将通过大型中生态系统的实验在受控环境中进行评估。这些实验将确定浮游生物对以下情况的反应：1.登陆压力的梯度，这将支持为期4年的LTREB鱼类模拟所包含的鲑鱼繁殖强度，以及，2.鲑鱼摄食量和NO_3负荷量的析因处理，旨在模拟高和低外部营养物负荷量和高和低鱼类存放量的组合。这些实验还提供了额外的舞台，在其中测试食物网动态和浮游植物群落结构的模拟模型的预测。城堡湖食物网的功能群模型、城堡湖食物网的多物种模型和浮游植物群落的多物种模型(在Powell和Richerson 1985年之后)将被开发出来，作为综合在我们基于机制的观察和实验计划期间获得的观察结果并推广所获得的见解的手段。参数和模拟条件将从具体的实验和长期数据集获得，并用于进一步探索群落过程(捕食、基于资源的竞争)与生态系统属性(年间和年内生产力的模式、NO3和NH4的作用等)之间的相互作用。

This proposal is designed to evaluate how community interactions (predation, competition) produce changes in ecosystem dynamics during a series of whole-lake food web manipulations. The work proposed capitalizes on a program of fish stocking manipulations funded by an LTREB grant from the National Science Foundation, as well as on the long-term record of data collection at this site. Detailed study of resource-and predator-relations of the dominant components of the food web will allow the investigators the mechanisms responsible for changes in each tropic level and ultimately in the ecosystem itself. Fish populations will be monitored by acoustics and video observation, as well as by more conventional fisheries techniques, and changes in abundances, growth, diets, recruitment, and degree of plankivory evaluated as major changes in external fish stocking intensity are imposed. Changes in zooplankton dynamics (especially of Daphnia) will also be examines using techniques of zooplankton population biology (egg ratios, estimates of birth and death rates) as well as physiological measures of food status (lipid content). The PI's will also evaluate the degree to which trout planktivory accounts for observed Daphnia mortality. Phytoplankton-predator relationship will be assessed by measuring grazing rates by zooplankton dominants on the major algal taxa and determining whether changes in situ algal dynamics are attributable to grazing impacts. Phytoplankton-resource relations will be evaluated by monitoring algal nutritional conditions and using dilution bioassays to determine species-specific growth kinetics for major limiting nutrients. In addition, the roles of externally-supplied N vs. internally-supplied N (i.e. within the food web) in supporting algal productivity will be evaluated using 15 N isotope techniques. The roles of planktivory and nutrient/food supply in altering plankton dynamics will be assessed in controlled settings by experiments in large mesocosms. These experiments will determine plankton responses to: 1. a gradient of lanktivory pressure which will bracket the intensity of trout redation to be encompassed by the 4-year LTREB fish anipulations, and, 2. a factorial manipulation of trout lanktivory and NO3 loading designed to simulate the combination of high and low external nutrient loading and high and low fish stocking. These experiments also provide additional arenas within which to test the predications of simulations models of food web dynamics and phytoplankton community structure. A functional group model of the Castle Lake food web and a multi-species model of the Castle Lake food web and a multi- species model of the phytoplankton community (following Powell and Richerson 1985) will be developed as means of synthesizing the observations obtained during our mechanism-based observational and experimental program and to generalize the insights obtained. Parameters and simulation conditions will be obtained from specific experiments and from the long-term data set and used to further explore the interactions between community processes (predation, resource-based competition) and ecosystem properties (patterns of inter-and intra-annual productivity, the role of NO3 and NH4, etc.)