Nestedness in assemblages of metazoan ecto- and endoparasites of marine fish.

Assemblages of metazoan ectoparasites of 79 species and gastrointestinal helminths of eight species of marine fishes were analysed to examine whether nestedness is related to sample size, abundance, species richness, and prevalence of infection, and whether the use of z-scores or Monte Carlo simulations yields different results. No significant differences in the number of nested assemblages were found with the two methods, and neither sample size nor abundance, but prevalence of infection of ectoparasites was correlated with nestedness. Species richness was significantly correlated with nestedness only when fish species with fewer than three parasite species were not excluded. Differential colonisation probabilities are the most likely cause of nestedness.