| The hierarchical nature of parasite populations and communities dictates interaction among elements comprising each focal level should be a significant contributor to the structure of individual communities. Empirical evidence has supported this contributor to the structure of individual communities. Empirical evidence has supported this conjecture, especially among traditionally-defined parasite component communities. Across landscapes, populations of an individual host species will encounter and interact with fundamentally different host communities, each constituting a different pool of parasite species from which a component community is assembled. Host specificity of parasites should then be a major determinant of the structure of component communities, with a sizeable proportion of the diversity and abundance of parasites in a component community derived from outside sources, i.e., other host taxa. This hypothesis was tested by examining the component communities of rosyside dace (Clinostomus funduloides) and redlip, shiners (Notropis chiliticus), and their relationship to the host communities, at 14 sites distributed among 7 low-order streams on the eastern slope of the Appalachian Mountains in northwestern North Carolina. In contrast to previous studies, little or no effect of host community composition, or of the total parasite community of fishes, was evident in the species richness or abundance of component communities. On the other hand, parasite species were arranged along a covarying continuum of distribution and abundance, and host specificity did provide predictive power to this relationship. Host generalists, which have broad resource ranges, are more widely distributed among sites and more locally abundant where they do occur than are host specialists. In contrast to most research on parasite communities, the present investigation found little pattern at the component community level; rather, most of the ecologically important optima existed at the next higher level in the hierarchy of parasite community organization. Independent research on the life cycle of Plagioporus sinitsini suggests that the pattern of distribution and abundance of parasites have multiple causes, and that the inability to accurately predict parasite abundance across a landscape might have its explanation in the evolved life histories of parasites interacting with a highly variable abiotic world, thus determining the probability of colonization, extinction, and the size of populations at individual locales. |
