Lampert Winfried, McCauley Edward, Manly Bryan F J
Max Planck Institute of Limnology, Postfach 165, 24302 Plön, Germany.
Proc Biol Sci. 2003 Apr 7;270(1516):765-73. doi: 10.1098/rspb.2002.2291.
Zooplankton vertical migratory patterns are a classic example of optimal habitat choice. We hypothesize that zooplankton distribute themselves vertically in the water column according to an ideal free distribution (IFD) with costs such as to optimize their fitness. In lakes with a deep-water chlorophyll maximum, zooplankton are faced with a trade-off, either experiencing high food (high reproductive potential) but low temperature (slow development) in the hypolimnion or high temperature and low food in the epilimnion. Thus, in the absence of fish predation (e.g. at night) they should allocate the time spent in the different habitats according to fitness gain dependent on the temperature gradient and distribution of food. We tested this hypothesis with a Daphnia hyalina x galeata clone in large indoor columns (Plön Plankton Towers) and with a dynamic energy budget model. In the tower experiments, we simulated a deep-water algal maximum below the thermocline with epilimnetic/hypolimnetic temperature differences of 2, 5 and 10 degrees C. Experimental data supported the model. We found a significantly larger proportion of daphniids in the hypolimnion when the temperature difference was smaller. Our results are consistent with the concept of IFD with costs originally developed for stream fishes. This concept can be applied to predict the vertical distribution of zooplankton in habitats where fish predation is of minor importance.
浮游动物的垂直洄游模式是最佳栖息地选择的一个经典例子。我们假设浮游动物会根据理想自由分布（IFD）在水柱中垂直分布，并考虑诸如成本等因素，以优化其适合度。在深水叶绿素最大值出现在深水层的湖泊中，浮游动物面临着一种权衡：要么在湖下层经历高食物量（高繁殖潜力）但低温（发育缓慢），要么在湖上层经历高温但食物量低。因此，在没有鱼类捕食的情况下（例如在夜间），它们应该根据依赖于温度梯度和食物分布的适合度增益，来分配在不同栖息地所花费的时间。我们用大型室内柱状装置（普伦浮游生物塔）中的透明溞×盔形溞克隆体以及一个动态能量预算模型对这一假设进行了测试。在柱状装置实验中，我们模拟了温跃层以下的深水藻类最大值，湖上层/湖下层的温度差分别为2℃、5℃和10℃。实验数据支持了该模型。我们发现，当温度差较小时，湖下层中的溞类比例显著更大。我们的结果与最初为溪流鱼类所提出的带成本的理想自由分布概念相一致。这一概念可用于预测在鱼类捕食不太重要的栖息地中浮游动物的垂直分布。
