Explaining parasite aggregation: more than one parasite species at a time

•Parasite-centric models are used to explore the effects of aggregation on coinfection.•Aggregation increases the probability and intensity of conspecific co-occurrence.•Aggregation lowers the probability, intensity and diversity of heterospecific infection.•In light of the results, generalizable adaptive benefits of aggregation are suggested.

Studies generally have neglected parasite-centric views in explorations of whether the oft-seen patterns of parasite aggregation are adaptive. Using simulation models, we explored the effects of aggregation on coinfection with hetero- or conspecific parasite species characterised by different mean abundances. Increasing aggregation increased the probability of conspecific co-occurrence for parasites with low mean abundances, and increased median numbers of conspecifics for all species. In comparison, increasing aggregation generally decreased the probability, intensity and diversity of heterospecific co-occurrence, irrespective of mean abundance. Researchers should weigh the respective costs and benefits of increasing co-occurrence with conspecifics and decreasing coinfection with heterospecifics in explaining aggregation.

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