"The animals, plants, and microbes most likely to disappear
as biodiversity is lost are often those that buffer infectious disease transmission. Those that remain tend to be species that magnify the transmission of infectious diseases like West Nile virus, Lyme disease, and hantavirus.
"We knew of specific cases in which declines in biodiversity increase the incidence of disease," says Felicia Keesing, an ecologist at Bard College in Annandale, N.Y., and first author of the paper. "But we've learned that the pattern is much more general: biodiversity loss tends to increase pathogen transmission across a wide range of infectious disease systems."
The pattern holds true for various types of pathogens -- viruses, bacteria, fungi -- and for many types of hosts, whether humans, other animals, or plants.
"When a clinical trial of a drug shows that it works," says Keesing, "the trial is halted so the drug can be made available. In a similar way, the protective effect of biodiversity is clear enough that we need to implement policies to preserve it now.""