Fritz Hervé, Said Sonia, Weimerskirch Henri
Centre d'Etudes Biologiques de Chizé, CNRS UPR 1934, 79360 Beauvoir-sur-Niort, France.
Proc Biol Sci. 2003 Jun 7;270(1520):1143-8. doi: 10.1098/rspb.2003.2350.
Foraging animals are expected to adjust their path according to the hierarchical spatial distribution of food resources and environmental factors. Studying such behaviour requires methods that allow for the detection of changes in pathways' characteristics across scales, i.e. a definition of scale boundaries and techniques to continuously monitor the precise movement of the animal over a sufficiently long period. We used a recently developed application of fractals, the changes in fractal dimension within a path and applied it to foraging trips over scales ranging across five orders of magnitude (10 m to 1000 km), using locations of wandering albatrosses (Diomedea exulans) recorded at 1 s intervals with a miniaturized global positioning system. Remarkably, all animals consistently showed the same pattern: the use of three scale-dependent nested domains where they adjust tortuosity to different environmental and behavioural constraints. At a small scale (ca. 100 m) they use a zigzag movement as they continuously adjust for optimal use of wind; at a medium scale (1-10 km), the movement shows changes in tortuosity consistent with food-searching behaviour; and at a large scale (greater than 10 km) the movement corresponds to commuting between patches and is probably influenced by large-scale weather systems. Our results demonstrate the possibility of identifying the hierarchical spatial scales at which long-ranging animals adjust their foraging behaviour, even in featureless environments such as oceans, and hence how to relate their movement patterns to environmental factors using an objective mathematical approach.
觅食动物预计会根据食物资源和环境因素的分层空间分布来调整其路径。研究这种行为需要能够检测不同尺度下路径特征变化的方法，即尺度边界的定义以及在足够长的时间内持续监测动物精确运动的技术。我们使用了一种最近开发的分形应用，即路径内分形维数的变化，并将其应用于跨越五个数量级（10米至1000公里）尺度的觅食行程，使用通过小型化全球定位系统以1秒间隔记录的漂泊信天翁（漂泊信天翁）的位置。值得注意的是，所有动物都一致呈现出相同的模式：使用三个依赖尺度的嵌套区域，在这些区域中它们根据不同的环境和行为限制来调整曲折度。在小尺度（约100米）下，它们采用曲折运动，因为它们不断调整以最佳利用风力；在中等尺度（1 - 10公里）下，运动的曲折度变化与觅食行为一致；而在大尺度（大于10公里）下，运动对应于斑块之间的往返，可能受大尺度天气系统影响。我们的结果证明了识别长距离动物调整其觅食行为的分层空间尺度的可能性，即使在像海洋这样无特征的环境中，从而展示了如何使用客观的数学方法将它们的运动模式与环境因素联系起来。
