Factors shaping the parasite communities of trout-perch, Percopsis omiscomaycus Walbaum (Osteichthyes : Percopsidae), and the importance of scale
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Trout-perch (Percopsis omiscomaycus Walbaum) provide a useful model in which to study fish-parasite communities because they have restricted trophic categories, they represent a single widely distributed taxon in North America, and numerous compound community surveys exist for comparison at the local and biogeographical scales. Forty-two species are reported from trout-perch, with 19 species known from Dauphin Lake, Manitoba, Canada. The most prevalent parasites species increased with host age, relating to increased food intake and (or) shifts in dietary preference towards larger food items. Randomization methods developed here demonstrate observed richness, and diversity patterns are nonrandom for local infracommunities and regional component communities. High mean overlaps, combined with high number of shared parasites and diversity estimates, indicate a predictable system. Schooling, maximum size, and age restricted the trout-perch diets to macroinvertebrates, resulting in extensive dietary sharing, which produced their homogenous infracommunities. Inshore-offshore diurnal movements combined with limited trophic categories revealed predictable component communities at the biogeographical scale. Eight parasites were predictable at the local scale and six at the regional scale (comprising two strictly host-specific species and four ecological species). Ecological predictability was determined by repeated predator-prey patterns, preferred host habitat, and niche sympatry. Trout-perch parasite communities, at both the local and regional scales, were determined by stable infracommunity processes and fish community complexity, which influence the component communities at the local scale.