Rifkin Joanna L, Nunn Charles L, Garamszegi László Z
Department of Human Evolutionary Biology, Harvard University, Peabody Museum, Cambridge, MA 02138, USA.
Am Nat. 2012 Jul;180(1):70-82. doi: 10.1086/666081. Epub 2012 May 23.
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 (on the basis of 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 metaregression 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, in which effect sizes are larger.
寄生现象被广泛视为社会性的主要代价以及对群体规模的一种限制，然而研究报告了群体规模与寄生现象之间存在多种不同的关联。我们利用同类中最大的数据库，对69项关于群体规模与寄生虫风险关系的研究进行了荟萃分析，寄生虫风险通过寄生现象和免疫防御来衡量。我们预测，对于表现出接触性传播和环境传播的生物，群体规模与寄生现象呈正相关；对于搜寻性寄生虫、寄生蜂以及可能的媒介传播寄生虫（基于遭遇稀释效应），群体规模与寄生现象呈负相关。总体而言，我们发现群体规模存在正向效应（r = 0.187），其大小在不同传播模式和寄生虫风险衡量指标之间有所变化，仅有微弱的发表偏倚迹象。在不同的宿主群体中，我们发现鸟类的群体规模与寄生虫风险之间关系比哺乳动物更强，这可能是由生态和社会因素驱动的。一项元回归分析表明，效应大小随最大群体规模增加。系统发育荟萃分析未发现群体规模与寄生现象关系强度存在系统发育信号的证据。我们得出结论，群体规模是寄生虫风险的一个弱预测指标，除了生活在大群体中的物种，如群居鸟类，在这些物种中效应大小更大。
