Group-size effects, whereby antipredator vigilance decreases as group size increases, are widely reported in mammals and birds but a meta-analysis has only been conducted in birds. We systematically reviewed the literature on mammalian group-size effects, estimated the effect sizes in each study, and conducted a phylogenetic meta-analysis. We obtained 296 effect sizes from 97 species belonging to 10 Orders and 26 Families. Overall, effect sizes indicated a moderate negative effect of group size (r = −0.44), but 43% of the effect sizes were compatible with a null effect of group size. There was significant heterogeneity in effect sizes. Weaker effect sizes occurred when vigilance was measured as a frequency or a duration rather than as a percentage of time spent vigilant, when measured in closed habitats, during the reproductive season, and in mixed-sex groups or during times when juveniles were absent. We infer a “file drawer problem” because there were relatively few studies with smaller sample sizes reporting small group-size effects. The results confirm the importance of group size in explaining variation in mammalian vigilance but also suggest which a substantial amount of variation remains unexplained. We suggest that future studies should aim to study mammalian group-size effects by quantifying the percentage of time allocated to vigilance rather than lower-power methods such as frequency or duration of vigilance.

中文翻译：

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群体规模对哺乳动物警觉性影响的荟萃分析

群体规模效应，即反捕食者的警惕性随着群体规模的增加而降低，在哺乳动物和鸟类中广泛报道，但仅在鸟类中进行了荟萃分析。我们系统地回顾了有关哺乳动物群体规模效应的文献，估计了每项研究中的效应规模，并进行了系统发育荟萃分​​析。我们从属于 10 个目和 26 个科的 97 个物种中获得了 296 个效应量。总体而言，效应大小表明组大小有适度的负面影响（r = -0.44），但 43% 的效应大小与组大小的无效效应相符。效应量存在显着的异质性。当警惕性被测量为频率或持续时间而不是作为警惕所花费时间的百分比时，会出现较弱的影响大小，当在封闭的栖息地测量时，在生殖季节，在混合性别群体中或在青少年缺席的时候。我们推断出“文件抽屉问题”，因为样本量较小的研究报告的小组规模效应相对较少。结果证实了群体规模在解释哺乳动物警惕性变化方面的重要性，但也表明哪些大量变化仍未得到解释。我们建议未来的研究应该旨在通过量化分配给警觉的时间百分比而不是诸如频率或警戒持续时间等低功率方法来研究哺乳动物群体规模的影响。结果证实了群体规模在解释哺乳动物警惕性变化方面的重要性，但也表明哪些大量变化仍未得到解释。我们建议未来的研究应该旨在通过量化分配给警觉的时间百分比而不是诸如频率或警戒持续时间等低功率方法来研究哺乳动物群体规模的影响。结果证实了群体规模在解释哺乳动物警惕性变化方面的重要性，但也表明哪些大量变化仍未得到解释。我们建议未来的研究应该旨在通过量化分配给警觉的时间百分比而不是诸如频率或警戒持续时间等低功率方法来研究哺乳动物群体规模的影响。