Data from: Are 2D space-use analyses adapted to animals living in 3D environments? A case study on a fish shoal

Methodologies enabling the monitoring of animal movement and behaviour in three-dimensions (3D; x, y, z, the latter accounting for the vertical dimension) are becoming increasingly accessible and can be deployed on entire groups of animals inhabiting 3D habitats. When two-dimensional (2D; x, y) space-use analyses are used on such groups, their spatial organisation is represented as a planar projection of individuals’ space-use. Movement on the vertical dimension is ignored and could biased ecological inference made from the spatial structure of the group. We used a digital imaging technique to track movements and feeding behaviour of individual animals within a free-range aggregation of juvenile drift-feeding fish (Galaxias anomalus) in 3D and at fine spatiotemporal scales. We estimated spatiotemporal overlap of space-use and feeding territories between group-members using 2D (x, y) and 3D spatial analysis to: (i) describe the spatial structure of the group, (ii) identify patterns of resource partitioning, and (iii) investigate the relationship between space-use overlap and feeding behaviour. We found that overlapping ratios of space-use and feeding territories were over-estimated in 2D, while 3D analysis of space-use provided evidence of spatial partitioning between group members. We also found that, regardless of the computation used, the overlapping ratios of space-use were positively correlated with overlapping ratios of feeding territories while no effect was found on feeding activity. In conclusion, whilst 3D analysis provided valuable information on the spatial structure of a group, inferences on the ecological function of space-use can also be obtained from 2D analysis.

能够在三维（3D；x、y、z，其中z代表垂直维度）环境中监测动物运动与行为的方法正变得愈发易于获取与应用，且可应用于栖息于三维生境中的整群动物。若针对此类群体采用二维（2D；x、y）空间利用分析，其空间组织会被表征为个体空间利用范围的平面投影，垂直维度上的运动被忽略，由此可能对基于群体空间结构所做出的生态学推论产生偏倚。本研究采用数字成像技术，在精细时空尺度下对自由活动的稚龄漂流食性鱼类安渡南乳鱼（Galaxias anomalus）的集群内个体运动与摄食行为开展三维追踪。我们分别采用二维（x、y）与三维空间分析手段，估算群体成员间空间利用与摄食领地的时空重叠度，以实现三大研究目标：（i）描述该群体的空间结构；（ii）识别资源分隔模式；（iii）探究空间利用重叠与摄食行为之间的关联。研究结果显示，二维分析会高估空间利用与摄食领地的重叠率，而三维空间分析则证实了群体成员间存在空间分隔现象。此外，无论采用何种计算方式，空间利用重叠率均与摄食领地重叠率呈正相关，但未对摄食活动产生显著影响。综上，尽管三维分析能够提供关于群体空间结构的宝贵信息，但依托二维分析同样可推导出有关空间利用生态功能的推论。