Spatial overlap between predator and prey is a prerequisite for predation, but the degree of overlap is not necessarily proportional to prey consumption. This is because many of the behavioural processes that precede ingestion are non‐linear and depend on local prey densities. In aquatic environments, predators and prey distribute not only across a surface, but also vertically in the water column, adding another dimension to the interaction. Integrating and simplifying behavioural processes across space and time can lead to systematic biases in our inference about interaction strength. To recognise situations when this may occur, we must first understand processes underlying variation in prey consumption by individuals. Here we analysed the diet of a major predator in the Barents Sea, the Atlantic cod Gadus morhua, aiming to understand drivers of variation in cod's feeding on its main prey capelin Mallotus villosus. Cod and capelin only partly share habitats, as cod mainly reside near the seafloor and capelin inhabit the free water masses. We used data on stomach contents from ~2000 cod individuals and their surrounding environment collected over 12 years, testing hypotheses on biological and physical drivers of variation in cod's consumption of capelin, using generalized additive models. Specifically, effects of capelin abundance, capelin depth distribution, bottom depth and cod abundance on capelin consumption were evaluated at a resolution scale of 2 km. We found no indication of food competition as cod abundance had no effect on capelin consumption. Capelin abundance had small effects on consumption, while capelin depth distribution was important. Cod fed more intensively on capelin when capelin came close to the seafloor, especially at shallow banks and bank edges. Spatial overlap as an indicator for interaction strength needs to be evaluated in three dimensions instead of the conventional two when species are partly separated in the water column.

中文翻译：

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捕食者与猎物的重叠在三个方面：鳕鱼从海底附近的毛鳞鱼中受益

捕食者与猎物之间的空间重叠是进行捕食的先决条件，但是重叠的程度不一定与猎物的消费成正比。这是因为摄入之前的许多行为过程都是非线性的，并且取决于本地猎物的密度。在水生环境中，捕食者和猎物不仅分布在整个表面上，而且垂直分布在水柱中，为交互增加了另一个维度。整合和简化跨时空的行为过程可能会导致我们对交互强度的推断存在系统偏差。为了识别可能发生这种情况的情况，我们必须首先了解个体捕食者消费变化的潜在过程。在这里，我们分析了巴伦支海主要捕食者的饮食，大西洋鳕鱼Gadus morhua旨在了解鳕鱼主要猎物毛鳞鱼Mallotus villosus的摄食变化的驱动因素。鳕鱼和毛鳞鱼仅部分共享栖息地，因为鳕鱼主要居住在海底附近，而毛鳞鱼则生活在自由水体中。我们使用了12年来收集的大约2000个鳕鱼个体及其周围环境的胃内容数据，并使用广义加性模型检验了鳕鱼毛鳞鱼食用量变化的生物学和物理驱动力假设。具体而言，在2 km的分辨率范围内评估了毛鳞鱼丰度，毛鳞鱼深度分布，底部深度和鳕鱼丰度对毛鳞鱼消耗的影响。我们没有发现食物竞争的迹象，因为鳕鱼的丰度对毛鳞鱼的消费没有影响。毛鳞鱼的丰富度对食用影响不大，而毛鳞鱼的深度分布很重要。当毛鳞鱼接近海底时，鳕鱼以毛鳞鱼为食，特别是在浅滩和河岸边缘。当物种在水柱中部分分离时，作为重叠强度指标的空间重叠需要从三个维度进行评估，而不是传统的两个维度。