On the other hand, the California tiger salamander was typically one of the last species to be added to a pond community--and also one of the most resistant to parasitic infection.
Therefore, in a pond with greater biodiversity, parasites have a higher chance of encountering an amphibian that is resistant to infection, lowering the overall success rate of transmission between infected snails and amphibians.
This same pattern--of less diverse communities being made up of species that are more susceptible to disease infection--may well play out in more complex ecosystems, Johnson said.
That's because species that disperse quickly across ecosystems appear to trade off the ability to quickly reproduce with the ability to develop disease resistance.
The recent study also reinforces the connection between deformed frogs and parasitic infection.
In the mid-1990s reports of frogs with extra, missing or misshapen legs skyrocketed, attracting widespread attention in the media and motivating scientists to try to figure out the cause.
Johnson was among the researchers who found evidence of a link between infection with Ribeiroia and frog deformities, though the apparent rise in reports of deformations, and its underlying cause, remained controversial.
While the new study has implications beyond parasitic infections in amphibians, it does not mean that an increase in biodiversity always results in a decrease in disease, Johnson said.
Other factors also affect rates of disease transmission.
For example, a large number of mosquitoes hatching in a particular year increases the risk of contracting West Nile virus, even if there has been an increase in the biodiversity of the bird population.
Birds act as "reservoir hosts" for West Nile virus, harboring the pathogen indefinitely with no ill effects, then passing on the pathogen.
"Our results indicate that
|Contact: Cheryl Dybas|
National Science Foundation