1. Foundational work has examined adaptive social behavior in animals in relation to the costs and benefits of group living. Within this context, a “group” of animals represents an organizational unit that is integral to the study of animal ecology and evolution.
2. Definitions of animal group sizes are often subjective with considerable variability within and across species. However, investigations of both the extent and implications of such variability in the estimation of animal group sizes are currently lacking.
3. Selecting ungulates as a case study, we conducted a literature review to assess prevailing practices used to determine group sizes among terrestrial Cetartiodactyla and Perissodactyla. Via this process, we examined group size definitions for 61 species across 171 peer‐reviewed studies published between 1962 and 2018.
4. These studies quantified group sizes via estimation of ungulate aggregations in space and time. Spatial estimates included a nearest neighbor distance ranging from 1.4 m to 1,000 m, and this variation was partially explained by a weak positive correlation (|r | = .4, p  < .003) with the body size of the ungulate research subjects. The temporal extent over which group size was estimated was even broader, ranging from three minutes to 24 hr.
5. The considerable variability in ungulate group size estimation that we observed complicates efforts to not only compare and replicate studies but also to evaluate underlying theories of group living. We recommend that researchers: (a) clearly describe the spatiotemporal extents over which they define ungulate group sizes, (b) highlight foundational empirical and ecological rationale for these extents, and (c) seek to align such extents among individual species so as to facilitate cross‐system comparisons of ungulate group size dynamics. We believe an integrative approach to ungulate group size estimation would readily facilitate replication, comparability, and evaluation of competing hypotheses examining the tradeoffs of animal sociality.

中文翻译：

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有蹄类动物种群大小估计的可变性使生态推断复杂化。

1. 基础工作已经研究了动物在适应群体生活的成本和收益方面的适应性社会行为。在这种情况下，一组动物代表了一个组织单位，是动物生态学和进化研究不可或缺的组成部分。
2. 动物群大小的定义通常是主观的，在种内和种间差异很大。但是，目前尚缺乏对这种可变性在动物群大小估计中的范围和影响的研究。
3. 选择无蹄类动物作为案例研究，我们进行了文献综述，以评估用于确定陆生Ce足纲和Perissodactyla群大小的流行做法。通过这一过程，我们检查了1962年至2018年间发表的171篇同行评审研究中61种物种的种群大小定义。
4. These studies quantified group sizes via estimation of ungulate aggregations in space and time. Spatial estimates included a nearest neighbor distance ranging from 1.4 m to 1,000 m, and this variation was partially explained by a weak positive correlation (|r | = .4, p  < .003) with the body size of the ungulate research subjects. The temporal extent over which group size was estimated was even broader, ranging from three minutes to 24 hr.
5. 我们观察到的有蹄类动物种群估计的相当大的可变性使不仅要比较和重复研究，而且要评估群体生活的基本理论的工作变得复杂。我们建议研究人员：（a）清楚地描述他们定义有蹄类动物种群大小的时空范围；（b）突出这些范围的基础经验和生态学原理；（c）寻求在各个物种之间调整这种程度，以利于有蹄类群种群动态的跨系统比较。我们认为，采用综合方法计算群体规模的估算将很容易地促进重复性，可比性和评估动物社会性权衡的竞争假设的评估。