The communities of helminth parasites of Heterandria bimaculata (Teleostei: Poeciliidae) from the upper Río La Antigua basin, east-central Mexico show a predictable structure.

We investigated a basic generalization in parasite community ecology stating that stochastic processes played a major part in determining the composition of helminth communities of freshwater fish, or on the contrary, if these communities are predictable, diverse and structured species assemblages. We determined the species pool of helminth parasites of a tropical freshwater fish Heterandria bimaculata in its heartland, the upper Río La Antigua basin in east-central Mexico. Approaching our data from the metapopulation standpoint we studied the spatial patterns, and examined the variation in composition and richness of the component communities across different locations. We tested the prediction that helminth species may be recognized as common or rare; and also two hypotheses anticipating depauperate communities and decay of similarity between component communities with increasing distance. We found these communities composed by a highly structured and predictable set of specialist autogenic helminth species that are constant and abundant, dominating all components throughout space. The prediction that it is possible to recognize common and rare species was met. Richer than expected communities were found, as well as highly homogeneous component communities, where neighbouring components were more similar than distant ones. We speculated that the processes shaping the development of these component communities include stable, predictable habitats through time, allowing for a slow gradual dispersion process limited by host and parasite species capabilities. Our study suggests that metapopulation theory can assist in the prediction of community composition and in the understanding of spatial and temporal community variability.