Do Animals Living in Larger Groups Experience Greater Parasitism? A Meta-Analysis

Abstract

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. abstract: 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 ( ) that varied in magr p 0.187 nitude 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.

Intestinal parasite communities of six sympatric lemur species at Kirindy Forest, Madagascar

“…However, a meta-analysis including a wide range of host species from mammals to insects revealed that effect sizes of group size on parasite species richness are generally low, except for animals living in large aggregations (Rifkin et al, 2012). In summary, there is overall support for an association between parasite risk and a gregarious lifestyle, but this relationship varies considerably across taxa (Rifkin et al, 2012).…”

Digging for answers: contributions of density- and frequency-dependent factors on ectoparasite burden in a social mammal

“…Nevertheless, three meta-analyses have demonstrated across a broad range of host species and parasite taxa that hosts living in larger groups generally suffer higher levels of parasitism (Côté and Poulin 1995;Rifkin et al 2012;Patterson and Ruckstuhl 2013). The strength of these patterns depends on the mode of transmission of the parasite with positive correlations being more apparent for directly transmitted parasites (Côté and Poulin 1995;Rifkin et al 2012;Patterson and Ruckstuhl 2013).…”

The sociality–health–fitness nexus: synthesis, conclusions and future directions

“…However, effects are not always as strong or consistent among studies as one might expect [21], including in the taxonomic groups in which social life is often viewed as most elaborate, i.e. primates [22,23].…”

“…While we might expect that animals living in a group will experience some increased exposure to infectious disease [18,21], the same is not true of social stress, where heterogeneity in responses might be more marked (e.g. in relation to dominance rank, see [7], with possibilities for both positive and negative effects).…”