NRS-hosted Parasites Receive Recognition on National “Stage”

The often-overlooked world of parasites made the news recently with the publication of “Homage to Linnaeus: How many parasites? How many hosts?” in the Proceedings of the National Academy of Sciences (PNAS). Article co-authors Andy Dobson, Kevin Lafferty, Armand Kuris, Ryan Hechinger, and Walter Jetz have attempted to quantify the number of parasitic species in the world and to estimate what impacts ongoing global extinctions will have on their numbers. Lafferty, Kuris, and Hechinger’s research, which focuses on several NRS coastal reserves, was featured in a 2007 NRS Transect cover article (“A Parasite’s World — Looking into the Planet’s Most Popular Lifestyle,” Transect 25:1, page 1).

Scientists estimate that the earth now supports approximately six million species of fauna. While admitting that the sampling of parasite diversity is extremely thin in key parts of the world, the authors estimate that about 40 percent of all known species are parasitic, including 75,000 to 300,000 helminth species (flat worms) that parasitize vertebrates. They also estimate that 3 to 5 percent of parasitic helminth species are threatened with extinction in the next 50 to 100 years, due to such factors as loss of host species.

Some may regard parasite extinctions as a loss mainly to parasitologists. The authors point out, however, that parasites provide a number of seldom-recognized ecosystem services, which will be lost without them. They estimate, for example, that more than 75 percent of links in natural food webs involve parasites. Furthermore, they point out that parasites regulate the relative abundance of free-living host species, while also concentrating and ultimately removing pollutants from their hosts.

This paper, which evolved from a presentation made at the Royal Swedish Academy during a symposium to celebrate the tercentenary of the birth of Linnaeus, can be seen at:
Dobson, A. P., K. Lafferty, A. Kuris, R. Hechinger, and W. Jetz. 2008. “Homage to Linnaeus: How many parasites? How many hosts?” PNAS 205:11482-11489.

The paper can also be accessed online at:
http://www.pnas.org/content/105/suppl.1/11482.full?sid=c6cee668-2813-4787-89d4-30f89213fb9a.

A PDF of the related Transect article can be accessed at:
http://nrs.ucop.edu/Transect-Carpinteria.htm.

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