Many metacommunities exhibit hierarchical structure, distributed across habitat patches that are themselves aggregated into groups. Perhaps the clearest example comes from multi-species assemblages of parasites, which occupy individual hosts that are aggregated into distinct host populations. At both spatial scales, we expect parasite community diversity in a given patch (host or population) to be influenced by patch characteristics that influence colonization rates and species sorting. What patch traits affect parasite community structure, and do these effects generalize across spatial scales (e.g., among individual hosts, versus among host populations)? To answer such questions, we described variation in parasite richness and community composition among host individuals, and among host populations, in a metapopulation of threespine stickleback (Gasterosteus aculeatus). We tested for variation in parasite communities as a function of individual host traits (ecomorphology, diet, size, sex, genotype at ~200,000 SNPs), and host population traits (mean morphology, mean diet, allele frequencies, and lake bathymetry).
Results/Conclusions
Examining each parasite taxon separately, we found substantial effects of host genotype, diet, ecomorphology, and sex on parasite prevalence. These host trait effects led to community-level patterns of species co-occurrence, because parasites with more similar host-trait associations tended to co-occur more often. The emergent result is that parasite community diversity also varied substantially among host individuals, and among host populations. This variation in diversity was also associated with host and environmental conditions. Some host traits (e.g., size, gape width) increase parasite richness at both spatial scales (among individual hosts, or among host populations). Other patch characteristics affect parasite richness only at the among-individual level (sex), or only among populations (lake size, lake area, elevation, and population mean heterozygosity). These results demonstrate that there are both scale-dependent and scale-independent processes governing parasite richness and composition at different spatial scales in this parasite metacommunity.