Biodiversity is, in most cases, good. And, as I’ve written before, biodiversity matters. In general, a healthy dose of biodiversity is something to strive for.
It can, as a recent study in Nature shows, even help fighting disease. (Warning: modest bullet point bonanza below.)
The researchers performed their investigation on three levels:
- First, sampling ‘in the wild’. Here, they looked at communities of amphibians in pond systems, ranging from 1 to 6 species and their interactions with a trematode (parasitic flatworms, aka ‘flukes’) pathogen bearing the name Ribeiroia ondatrea that can result in death or malformation.
Pacific Tree Frog with malformation caused by R. ondatrae, the villain of today’s tale. (Goodman & Johnson, 2011, click image)
- Second, outdoor mesocosm experiments, in which natural communities were mimicked and infections (both in total and per individual) were assessed.
- Finally, in the lab, where the number of species was manipulated (from 1 to 3) and the effects of this increase on disease transmission was studied.
So, what did they find? Without going into too much detail, these general findings were, well, found:
- At all three levels of investigation (wild, mesocosm and lab), more amphibian species meant lower pathogen transmission.
- As diversity decreased, the proportion of the most competent host species (or the best home for the parasite) increased.
- And, in more diverse communities, the transmission of the parasitic flatworm from snails (another intermediate host, or temporary station, for the parasite) to amphibians decreased.
R. ondatrae life cycle. (Johnson lab, University of Colorado, click image)
Two important remarks from the authors:
- Here, the amount of potential hosts affected the travel success of the parasite between its two temporary stations (end station: mammal or bird) seems to be the main mechanism leading to lower infection in diverse communities. Other mechanisms are possible, so field-based estimates of other host-pathogen systems are important to capture the dynamics of the system and begin crafting a general explanation.
- The effects of diversity on disease depend on what you’re measuring. An example they give is that host and parasite diversity often tend to increase in concert. But, parasite diversity need not correlate with disease risk, as parasites can vary in virulence and relative abundance.
In conclusion:
In light of mounting evidence that higher biodiversity can buffer against pathogen exposure in human, wildlife and plant disease systems, preserving functional diversity—including both genetic diversity and community richness—has the potential to ameliorate pathogen transmission and offer a novel, cost-effective approach to disease management.
For some more information on how biodiversity can influence human health, I’ve added two additional references below, which should be freely accessible to all.
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Johnson PT, Preston DL, Hoverman JT, & Richgels KL (2013). Biodiversity decreases disease through predictable changes in host community competence. Nature, 494 (7436), 230-233 PMID: 23407539
Additional references:
Chivain, E. (ed.) (2002). Biodiversity: Its Importance to Human Health. Interim Executive Summary. Center for Health and the Global Environment, Harvard Medical School.
Díaz, S., Fargione, J., Chapin, F., & Tilman, D. (2006). Biodiversity Loss Threatens Human Well-Being PLoS Biology, 4 (8) DOI: 10.1371/journal.pbio.0040277
