Abstract The vertical distribution of planktonic animals, such as Daphnia, in overlapping gradients of food concentration and risk of visual predation should depend on Daphnia population density and should be the result of the group effect of optimizing decisions taken by each individual (juvenile or adult), trading-off a high growth rate to low mortality risk. We tested this hypothesis by comparing the theoretical distributions from simulations based on an experimentally parameterized, optimizing individual-based model (consistent with the assumptions of the concept of the interference ideal free distribution with costs) with distributions observed in laboratory experiments. The simulations were generated for two scenarios, where the shape of the functional response of fish is consistent with either type II or III. The results confirmed the hypothesis. The greatest similarity of the distributions obtained in the experiments and simulations was found for the simulations based on the scenario assuming the type III rather than type II for both age classes of Daphnia. This was consistent with the results of the experiments for the model parameterization, which revealed the type III functional response of fish. Therefore, the results suggest that aggregating may be maladaptive as an anti-vertebrate-predation defense in the case of zooplankton.

中文翻译：

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水蚤在捕食风险下的理想自由分布——模型预测与实验验证

摘要 浮游动物（例如水蚤）在食物浓度和视觉捕食风险的重叠梯度中的垂直分布应取决于水蚤种群密度，并且应该是每个个体（少年或成年）做出的优化决策的群体效应的结果。 ，在高增长率与低死亡率风险之间进行权衡。我们通过比较基于实验参数化、优化基于个体的模型（与具有成本的无干扰理想分布的概念的假设一致）的模拟的理论分布与实验室实验中观察到的分布来测试这一假设。模拟是针对两种情况生成的，其中鱼的功能响应的形状与类型 II 或 III 一致。结果证实了这个假设。对于基于假设水蚤两个年龄级别的 III 型而不是 II 型的情景的模拟，发现在实验和模拟中获得的分布的最大相似性。这与模型参数化实验的结果一致，揭示了鱼的 III 型功能反应。因此，结果表明，在浮游动物的情况下，聚集可能是一种适应不良的反脊椎动物捕食防御措施。这揭示了鱼的 III 型功能反应。因此，结果表明，在浮游动物的情况下，聚集可能是一种适应不良的反脊椎动物捕食防御措施。这揭示了鱼的 III 型功能反应。因此，结果表明，在浮游动物的情况下，聚集可能是一种适应不良的反脊椎动物捕食防御措施。