Patterns of macroparasite abundance and aggregation in wildlife populations: A quantitative review

In this paper we review the published literature on patterns of abundance and aggregation of macroparasites in wildlife host populations. We base this survey on quantitative analyses of mean burden and a number of measures of the degree of aggregation of parasite burdens between hosts. All major parasite and vertebrate host taxa were represented in the database. Mean parasite burden was found to be log-normally distributed, indicating that all parasite burdens are regulated to some degree. In addition, all but one of the parasitic infections were aggregated with respect to their hosts, and the relationship between log mean parasite burden and log variance was found to be very strong (R(2) = 0.87). That is, for a given mean parasite burden there are constraints on the degree of variation in individual host burdens. The aggregated nature of the parasitic infections is also apparent from other measures of the degree of aggregation: prevalence - mean relationships, and the negative binomial parameter, k. Using a relatively new technique for parasitological infection data - tree-based models, as well as traditional linear models - a number of the parasitic infections was found to be associated with systematically lower or higher parasite burdens. Possible biological explanations for these and other patterns are proposed.