Data from: Do animals living in larger groups experience greater parasitism? A meta-analysis

Parasitism is widely viewed as the primary cost of sociality and a
constraint on group size, yet studies report varied associations between
group size and parasitism. Using the largest database of its kind, we
performed a meta-analysis of 69 studies of the relationship between group
size and parasite risk, as measured by parasitism and immune defenses. We
predicted a positive correlation between group size and parasitism with
organisms that show contagious and environmental transmission, and a
negative correlation for searching parasites, parasitoids, and possibly
vector-borne parasites (based on the encounter-dilution effect). Overall,
we found a positive effect of group size (r=0.187) that varied in
magnitude across transmission modes and measures of parasite risk, with
only weak indications of publication bias. Among different groups of
hosts, we found a stronger relationship between group size and parasite
risk in birds than in mammals, which may be driven by ecological and
social factors. A meta-regression showed that effect sizes increased with
maximum group size. Phylogenetic meta-analyses revealed no evidence for
phylogenetic signal in the strength of the group size-parasitism
relationship. We conclude that group size is a weak predictor of parasite
risk except in species that live in large aggregations, such as colonial
birds, where effect sizes are larger.

寄生现象普遍被视为社会性行为的主要代价，同时也是群体规模的制约因素，但现有研究关于群体规模与寄生现象间的关联呈现出多样的结果。本研究依托同类研究中规模最大的数据库，针对69项以寄生程度与免疫防御水平为衡量指标、探讨群体规模与寄生虫风险之间关系的研究开展了元分析。我们提出如下预测：对于存在接触传播与环境传播的生物而言，群体规模与寄生现象呈正相关；而对于搜寻性寄生虫、寄生性天敌以及可能的媒介传播寄生虫（基于遭遇稀释效应），二者则呈负相关。整体而言，我们发现群体规模存在正向影响（相关系数r=0.187），且该影响的强度因传播模式与寄生虫风险衡量指标的不同而存在差异，仅存在微弱的发表偏倚迹象。在不同宿主类群中，鸟类群体规模与寄生虫风险间的关联强度强于哺乳动物，这一现象或由生态与社会因素驱动。元回归分析显示，效应量随最大群体规模的增大而提升。系统发育元分析结果表明，群体规模与寄生现象的关联强度中未发现系统发育信号。我们得出结论：除了群居鸟类这类生活在大型集群中的物种（此类物种的效应量更大）之外，群体规模仅能作为寄生虫风险的弱预测因子。