Evaluating community structure and the role of regional and local processes in larval trematode metacommunities of Helisoma trivolvis

Background/Question/Methods

Metacommunity theory has advanced our understanding of how local and regional processes affect the structure of ecological communities.  While complex life cycle parasites have largely been omitted from metacommunity research, parasite communities make an interesting study system for evaluating metacommunity patterns.  Here, we used assemblages of trematode parasites that infect freshwater snails (Helisoma trivolvis) to evaluate three questions: (1) What factors affect individual host infections within wetlands? (2) Are parasite communities structured among wetlands? And (3) What is the relative role of local versus regional processes in determining community structure and species richness among wetlands?  We examined 10,821 snails from 120 sites in five park complexes in the San Francisco Bay area, California, and found 953 infections from six parasite groups. 

Results/Conclusions

At the within-wetland level, infection status of host snails correlated strongly with individual snail size and wetland infection prevalence for all six parasite groups.  Using reciprocal averaging to test for community structure, we found that larval trematode parasite metacommunities exhibited a quasi-nested structure with significant coherence.  Based on a model selection approach on generalized linear mixed models representing local and regional factors, parasite species richness and community structure correlated with both local abiotic (pond pH, surface area, and total dissolved nitrogen) and biotic (non-host mollusk density, and H. trivolvis biomass) factors.  Overall, trematode communities were consistent with an interactive community that most closely followed the predictions from the species sorting or mass effects metacommunity paradigm.  We suggest that parasite communities are useful systems for evaluating metacommunity concepts.