Body size vs abundance among parasite species: positive relationships?

Across species, abundance usually correlates negatively with body size. This intuitive pattern may result from size-dependent resource requirements in habitats where only finite amounts of resources are available. Among parasite species, it is possible that some resource limitations are less severe than for free-living animals although this may depend on the type of parasites. The interspecific relationship between body size and abundance (measured as prevalence and intensity of infection) among parasites was tested in two groups of parasites. Among helminth endoparasites of fish, parasite body size correlated positively with prevalence and negatively with intensity of infection. Among copepod ectoparasites of fish, body size correlated positively with both prevalence and intensity. These trends were observed after controlling for the confounding influences of phylogeny and sampling effort. These contrasting patterns may result from the more intense link between body size and intensity-dependent regulation in endoparasites than in ectoparasites. The results of this comparative analysis suggest that parasite body size could be an important factor determining aspects of parasite abundance and distribution, including aggregation.