Each year, my laboratory works on a group project to address a question that would be challenging to address by any individual alone.  Previous laboratory projects were featured on the cover of Nature (McMahon et al. 2014).  We recently set out to evaluate the generality of the dilution effect, the hypothesis that biodiversity reduces disease risk and thus, that human-induced biodiversity loss is facilitating increases in parasites.  Using a meta-analysis of 202 effect sizes on 61 parasite species, we provide broad evidence that host diversity inhibits parasite abundance.  The strength of this effect did not depend on whether the studies were observational or experimental, suggesting that dilution effects are common in nature.  Much of the controversy surrounding the dilution effect has been for zoonotic diseases of humans.  However, we documented similar effects of biodiversity on parasites that infect wildlife and on parasites that infect humans, implying that biodiversity loss may increase human disease risk.  Additionally, the dilution effect increased with decreasing host frequency, but did not depend on host density or any other contexts examined, indicating that dilution was robust across ecological contexts. In a second analysis, we found a similar relationship between plant diversity and herbivore pest abundance, suggesting a general effect whereby diversity in a community reduces the abundance of the community’s natural enemies. This latter result has obvious implications for crop production and thus feeding 9 billion people in the next 50 years.  Taken together, these results suggest that human-driven losses of biodiversity could increase the risk of disease outbreaks, with consequences for both agriculture and human health, and that biodiversity conservation might yield a promising strategy for mitigating these effects.

Although, on average, biodiversity might decrease parasite abundance, this is a probabilistic phenomonen. In some cases, increases in biodiversity could increase disease. Hence, we have conducted research in an effort to understand when biodiversity will increase and decrease disease and the traits of organisms that will dictate their potential to dilute or amplify disease risk. We encourage and are attempting to move towards a more mechanistic understanding of how biodiversity affects disease risk.

Sample Publications

Civitello, D.J., Cohen, J., Fatima, H., Halstead, N.T., Liriano, J., McMahon, T.A., Ortega, C.N., Sauer, E., Sehgal, T., Young, S., Rohr, J.R. 2015. Biodiversity inhibits parasites: broad evidence for the dilution effect. Proceedings of the National Academy of the United States of America 112: 8667–8671 (showcased by commentaries in PNAS and Science, double star recommendation by Faculty 1000, Altmetric score of 177, 99th percentile)

Dobson, A.P, Cattadori, I. Holt, R.D., Ostfeld, R.S., Keesing, F., Krichbaum, K.*, Rohr, J.R., Perkins, S.E., Hudson, P.J. 2006. Sacred cows and sympathetic squirrels: The importance of biological diversity to human health. PLoS Medicine 3: 714-718

Sears, B.F., Snyder, P.W., Rohr, J.R.¥ 2015. Host life-history and host-parasite syntopy predict behavioral resistance and tolerance to trematode parasites. Journal of Animal Ecology 84:625-636 (Runner-up for best student paper award 2015 from the Disease Ecology Section of the Ecological Society of America)

Rohr, J.R., Civitello, D.J., Crumrine, P.W., Halstead, N.T., Miller, A.D, Schotthoefer, A.M., Stenoien, C., Johnson, L.B., Beasley, V.R. 2015. Predator diversity, intraguild predation, and indirect effects drive parasite transmission. Proceedings of the National Academy of the United States of America 112:3008-3013 (Altmetric score of 68, 97th percentile)

Civitello, D.J., Rohr, J.R. 2014. Disentangling the effects of parasite exposure and host susceptibility on parasite transmission: an illustration with the human zoonotic parasite, Schistosoma mansoni. Journal of Animal Ecology 83:1379–1386

Venesky, M.D., Liu, X., Sauer, E., Rohr, J.R. 2014. Linking manipulative experiments to field data to test the dilution effect. Journal of Animal Ecology 83:557-565

Johnson, P.T.J., Rohr, J.R., Hoverman, J.T. Kellermanns, E., Bowerman, J., Lunde, K.B. 2012. Living fast and dying of infection: Host life history drives interspecific variation in infection and disease risk. Ecology Letters 15: 235-242 recommended by Faculty 1000

Martin, L.B., Hopkins, W.A., Mydlarz, L.D., Rohr, J.R. 2010. The effects of anthropogenic global change on immune functions and disease resistance. Annals of the New York Academy of Sciences: The Year in Ecology and Conservation Biology 1195: 129-148

For a full list of publications, please see the Publications page on this website.