General laws in ecological parasitology are scarce. Here we evaluate datapublished by over 100 authors to determine whether the number of hosts in alife cycle is associated with the degree of aggregation of fish parasites atdifferent stages. Parasite species were grouped taxonomically to produce 20 ormore data points per group as far as possible. Most parasites that remained atone trophic level were less aggregated than those that had passed up a foodchain. We use a stochastic model to show that high parasite overdispersion inpredators can be solely the result of the accumulation of parasites in theirprey. The model is further developed to show that a change in the predatorsfeeding behaviour with age may further increase parasite aggregation.
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