Spatial and seasonal variation in host community structure is weakly concordant with patterns of parasite composition

Abstract Parasites are known to respond strongly to changes in host diversity and may ultimately reflect changes in ecosystems. However, it remains unclear whether strong relationships between host and parasite richness also reflect those at the level of community composition. A complementary approach is to test for concordance between host and parasite composition to evaluate whether shifts in parasite community structure mirror patterns of their hosts and potentially the environment. I tested for concordance between patterns of community similarity in parasites, their fish hosts, and environmental factors sampled across three sites and four seasons within each of two river ecosystems. I constructed ordinations of parasites, fish, and environmental variables to establish their patterns of similarity in multivariate space and used Procrustes analysis to evaluate whether patterns in community structure were concordant. Spatial and seasonal patterns in fish and parasite community structure were concordant when analysing patterns in community composition (i.e. presence–absence), but not community abundance (i.e. numerical density). Patterns in fish communities were concordant with the physical river environment. However, despite finding concordance between fish and parasite communities and fish and their environment, parasites were concordant with the river environment in only one ecosystem. Re‐evaluating the relationship between host and parasite diversity under a community concordance framework showed that patterns among host and parasite community composition exist, but this relationship is weaker than expected. The looser connection between patterns in host and parasite community composition can be mediated by parasite life history and parasites responding both indirectly and directly to changes in host communities and the local environment.