How can a more diverse ecological community reduce parasite transmission?

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Ecologists have increasingly focused on the hypothesis that community diversity can influence infection levels and disease—the “dilution effect.” Biodiversity loss, a widespread consequence of environmental change, can in turn indirectly increase disease, including diseases of medical and veterinary importance.

Much of this research has focused on correlational studies of vector-borne microparasite diseases, such as Lyme disease and West Nile virus. The authors argue that parasites with complex life cycles—including helminths, protists, myxosporeans, and many fungi—offer an excellent additional model for experimentally investigating the mechanisms underlying the dilution effect.

This research synthesis brings together recent ecological research on the dilution effect in microparasites and decades of parasitological research on the decoy effect in macroparasites to explore how community structure relates to disease. It finds consistent evidence that community diversity significantly alters parasite transmission and pathology under both laboratory and natural conditions.

Empirical examples and simple transmission models highlight multiple mechanisms for these changes, typically involving predators, parasite decoys, hosts with low competence for transmission, or other parasites. However, the degree of transmission reduction varies among diluting species, between parasite stages, and across spatial scales. This variation makes quantitative, taxon-specific predictions about disease difficult.

Overall, the synthesis highlights a broad link between community structure and disease. It also emphasizes the importance of mitigating ongoing changes in biological communities caused by species introductions and local species losses.