Integrative Foraging in Complex Landscapes: Nutrient acquisition and mixing across food patches at the primary producer-Daphnia interface

消费者，如重要的水生食草动物水蚤，不断经历空间和时间变化的食物供应和质量。根据观测尺度的不同，这种变化是由各种因素驱动的，如藻类物种的演替、非生物因素（光、营养）的变化和/或不同质量食物斑块之间的移动。因此，水蚤对限制性营养物质的吸收是暂时波动的，在共同限制性营养物质的情况下，吸收甚至可能脱钩。在如此复杂的营养环境中，仅根据实验室营养研究来预测水蚤的反应是很困难的，因为食物质量是保持不变的，并且是根据准时（通常是非常遥远的）对植物营养质量的估计。预测水蚤的反应需要了解(a)与水蚤相关的资源如何在时间尺度上波动，以及(b)水蚤如何将这种时空异质性资源整合为长期适应性，即在不同斑块中获得的营养如何被吸收、储存、混合并用于生长和繁殖。本项目旨在描述研究较少但与水蚤相关的海藻营养品质（磷、必需脂肪酸和甾醇含量）的自然变异性，以小时和日为尺度。此外，通过一系列的生命表实验，我们旨在了解共同限制养分吸收的波动和解耦如何影响水蚤的生长速度、繁殖力和养分同化效率。最后，该项目还旨在增加对水蚤消化酶生理学的非常有限的了解，这可能是他们从不断波动的饮食中优化获取各种营养的最重要工具。我们期望该项目的结果将提高我们对浮游动物资源质量的时间和/或空间异质性的理解。此外，还将获得关于如何平均这种异质性以获得浮游动物总体栖息地质量的估计的知识，这对准确建立模型至关重要。

Consumers such as the keystone aquatic herbivore Daphnia, continuously experience spatial and temporal variability in their food availability and quality. Depending on the observational scale, this variability is driven by various factors such as successions in algal species, variation of abiotic factors (light, nutrients) and/or to movements between food patches of different quality. As a result, the uptake of limiting nutrients by Daphnia is temporally fluctuating and in the case of co-limiting nutrients the uptake might even be decoupled. In such complex nutritional environments, it is difficult to predict Daphnia responses only based on lab nutrition studies were food quality is kept constant and on punctual (and usually very distant) estimates of seston nutritional quality. Predicting Daphnia responses, requires understanding (a) how the resources fluctuate at temporal scales which are relevant to Daphnia, and (b) how Daphnia integrate such spatio-temporally heterogeneous resources into long-term fitness i.e. how nutrients acquired in different patches are be taken up, stored, mixed and used for growth and reproduction. This project aims to characterise the natural variability of the nutritional quality (in terms of Phosphorus, essential fatty acids and sterol contents) of seston at the poorly studied, but relevant to Daphnia, hourly and daily scale. Additionally, through a series of life table experiments, we aim to understand how fluctuation and decoupling in the uptake of co-limiting nutrients affect Daphnia growth rates, fecundity and nutrient assimilation efficiency. Finally, this project also aims to increase the very limited knowledge on Daphnia digestive enzyme physiology, which might potentially be their most important tool for optimizing the acquisition of various nutrients from a continuously fluctuating diet. We expect that outcomes of the project will improve our understanding of the scale at which temporal and/or spatial heterogeneity in resource quality matters for zooplankton. Moreover knowledge will be gained on how such heterogeneity should be averaged to obtain estimates of the overall habitat quality for zooplankton which is essential for accurate model building.