OULD ELIMINATE A SPECIES P THAT TRANSMITS DISEASE TO

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draws on the research and expertise of more than 100 scientists. But rather than a dry academic text, it takes the form of a richly illustrated coffee table book with chapter authors writing in language accessible to a general audi- ence as well as their fellow scientists. “Above all,” Chivian explains, “we’re trying to reach beyond specialists to help everyone grasp the urgencies involved in species loss.” It’s no coincidence that in 1985 Chi-

vian shared a Nobel Peace Prize for cofounding the International Physi- cians for Prevention of Nuclear War. That same year, he recalls, scientists discovered an ozone hole widening over the Antarctic. Concerns about climate change quickly followed. “By the 1990s, there was a growing

awareness among physicians in the anti-nuclearmovement thatwe had to enlarge our perspective to include global environmental changes,” Chi- vian says. “We saw these changes as Armageddon in slow motion, some- thing that would affect the globe in ways just as catastrophic as nuclear war.” In particular, researchers began uncovering how biodiversity losses appear to fuel the rise and spread of many infectious diseases. Chivian and others are also trying to raise aware- ness of how widespread extinctions hamper medical research.

DIVERSITY AND DISEASE Imagine a newly hatched tick resting on the floor of a northeastern U.S. for- est, waiting for its first blood meal. If the larval tick is in a fragmented or oth- erwise degraded patch of woods, the first host it encounters will probably be a white-footed mouse. As a result, the tick will likely become infected with the Lyme disease microbe, Borrelia burgdorferi. In much of the United

C IN THEORY, BIODIVERSITY LOSS EOPLE, BUT SCIENTISTS

States, up to 80 percent of white-footed mice carry this disease-causing bac- terium, which they pass to deer and humans via the bite of infected ticks. Now consider the same newly

hatched tick in an undisturbed forest. Here its first host is more likely to be an opossum, raccoon, ground bird, lizard or other non-mouse host. None are good carriers of the Lyme disease bacterium. As a result, the tick will likely escape infection and never transmit the disease to anyone. In 2000, animal ecologist Richard

Ostfeld described this Lyme disease- blocking dynamic and dubbed it the “dilution effect.” In essence, he explains, the greater a habitat’s biodi- versity, themore likely that an animal- borne microbe such as B. burgdorferi will end up in a dead-end host—one that does not pass it along. In theory, says Ostfeld, biodiversity

loss could eliminate a species that transmits disease to people. But scien- tists are not seeing this, he adds.When tropical deforestation decreases mos- quito diversity, for example, surviving mosquito species tend to be more- effective carriers of malaria. “It may be that there is something about the kind of weedy species that survive in disturbed areas,” Ostfeld says. One idea worth investigating, he proposes, is that fast-growing, fast-breeding organisms are by nature less resistant to disease. Making matters worse, such plants and animals often worsen diversity loss by outcompeting species more sensitive to human disturbance. Since Ostfeld’s landmark study,

other researchers have extended his findings to diseases such as West Nile virus, hantavirus pulmonary syndrome and malaria. In each case, the loss of biodiversity in an area leaves behind a few species that are more apt to trans-

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TOP, MICHAEL P. GADOMSKI (PHOTO RESEARCHERS); LEFT, BRIAN CONDON; FAR LEFT, TIMOTHY P. VIDRINE