Parasites of introduced species

We compiled species richness and prevalence data from parasitological studies of 26 invasive species from seven taxa (molluscs, crustaceans, fishes, birds, mammals, amphibians and reptiles) examined in their natural habitats. In order to compare parasite measures across the diverse range of host taxa studied (which varied in their parasite richness), we standardized parasite species richness (SPSR) for each population of hosts within each study as a proportion relative to the total number of parasite species found in all studies within the native range of that host species. In addition, we compared both mean prevalence (averaged across parasite species for each host species and the summed prevalence (sum of all parasite species for each host species). The latter measure gives an indication of the cumulative extent of parasitism (or potential impact of parasitism on a host population) that each host experiences14. For each of these metrics, we estimated the proportional parasite release experienced by introduced species as: (N-I)/N, where N is the value for the native range and I is the value for the introduced range of the above metrics.