Is there a fixed number of niches for endoparasites of fish?

Kennedy and Guégan, based on Cornell and Lawton (J Anim Ecol 1992;61:1-12), found a "curvilinear" relationship (the "fundamental form" of the relationship for parasite communities) between infracommunity and component community richness, and interpreted this as meaning that only processes acting within the infracommunities can explain the limitation in the number of parasite species in a given host. The research described here shows that an asymptotic relationship is the consequence of the differential likelihoods of parasite species to appear in an infracommunity as determined by transmission rates and intrinsic lifespans. Processes operating at the infracommunity level are not necessary to explain the curvilinear relationship. Even communities much richer than those found in European freshwater fishes cannot be assumed to be "saturated" in the sense that further species cannot be added over evolutionary time.