The relationship between pattern and scale in parasite communities: a stranger in a strange land

Abstract

Problems of pattern and scale are considered in relation to helminth communities of freshwater fish by examining them at different hierarchical taxonomic and spatial scales, with a view to seeking generalizations of heuristic value, assessing the importance of phylogenetic and ecological determinants of community structure and improving understanding of unpredictable communities. Initially, communities were analysed at the level of salmonid genera, focusing on Oncorhynchus, in its heartland in Canada: then in O. mykiss throughout its global range and finally in individual localities to which it has been introduced in Britain. In the heartland, communities are dominated by salmonid specialist helminths, forming a phylogenetic element: the minority ecological element comprises broad generalists and non-salmonid specialists. Most species except generic specialists are shared between host genera. As the distance to which O. mykiss was translocated from its heartland increases, so generic specialists disappear first and then salmonid specialists decline. The community is thus increasingly composed of generalists and it also becomes increasingly poor. Helminths may be acquired from native salmonids and/or unrelated hosts, depending on availability. This same pattern is paralleled in individual localities in a restricted region: the phylogenetic element reflects the native salmonid species present and the ecological element the presence of other genera of fish; i.e., a supply-side situation. The change of scale in analysis has thus enabled the recognition of generalizations and patterns of heuristic value and improved the understanding of unpredictable communities by interpreting local variation as ecological 'noise' that often obscures fundamental patterns. In this and other taxa of fish, phylogenetic elements dominate helminth communities in the heartlands, but ecological elements dominate as the host increasingly becomes a stranger in a strange land.

Diversity of intestinal helminth communities of carp from six lakes in the flood plain of the Yangtze River, China

“…A rich parasite community has been related to old host species (Brooks & McLennan, 1993) and to the species being in their heartland (Kennedy & Bush, 1994), and both hypotheses may provide an explanation for the rich intestinal helminth communities observed in the present study. In addition, the observed richness may also confirm the prediction by Guégan & Kennedy (1993) that fish species in their native habitats may harbour richer helminth communities.…”

Metazoan parasite fauna of two peacock-bass cichlid fish in Brazil

“…In agreement, Torchin et al (2003) reported a lower parasite diversity in invader regions, where hosts were recently introduced, than in others where they were not, supporting the theory of parasite loss through the invasion process. Kennedy and Bush (1994) argued that the parasite species more easily lost through the invasion process will be the ones more strictly dependent on a narrow range of host taxa to spread out and survive (i.e. more specialized parasites).…”

Similarities among ectoparasite fauna of sigmodontine rodents: phylogenetic and geographical influences

“…In contrast, the loss of an associated parasite species can occur through historical 'accidents' (e.g., the abrupt division of a host population in which a founding population becomes isolated and free of a specific parasite species) or by the dispersal of the host species to new environments, which present unfavourable conditions for some parasite species (e.g., the absence of an appropriate intermediate host in the new environment) (Hafner and Page, 1995;Paterson et al 1999). Because of these processes, the composition of the parasite fauna for a particular host species is a result of both its phylogenetic identity and its environment (Kennedy and Bush, 1994). Accordingly, the phylogenetic effect is expected to manifest through a greater compositional similarity among the parasites of host species with closer phylogenetic relatedness.…”