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.

可在三维（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日益普及，且可应用于栖息于三维生境中的整个动物集群。若对这类集群使用二维（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的平面投影，垂直维度上的运动被忽略，这可能会导致基于集群空间结构得出有偏的生态学推断。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幼年漂流食性鱼类——异纹南乳鱼（Galaxias anomalus）——集群内的个体运动与取食行为进行追踪。我们分别采用二维（2D; x、y）与三维（3D）空间分析方法，估算集群成员间的空间利用与取食领地的时空重叠度，以实现三大研究目标：（i）描述该鱼类集群的空间结构；（ii）识别资源分隔模式；（iii）探究空间利用重叠度与取食行为之间的关联。研究结果表明，二维分析会高估空间利用与取食领地的重叠度，而三维空间分析则证实集群个体间存在空间分隔现象。此外，无论采用何种计算方式，空间利用重叠度均与取食领地重叠度呈显著正相关，但对取食活动无显著影响。综上，尽管三维分析能够提供关于集群空间结构的关键信息，但基于空间利用的生态学功能推断也可通过二维分析获得。