Next Century May Bring Doom To Many Parasites, and Hosts
One in three parasite species may go extinct in the next century.
Scientists who studied what climate change may do to the world’s parasites came to a startling conclusion: one in three species may go extinct in the next century.
As global warming raises the planet’s temperature, the researchers found, many species will lose territory in which to survive. Some of their hosts will be lost, too.
“It still absolutely blows me away,” said Colin J. Carlson, lead author of the study and a graduate student at the University of California, Berkeley. He knows many people may react to the news with a round of applause.
“Parasites are obviously a hard sell,” Mr. Carlson said.
But as much as a tapeworm or a blood fluke may disgust us, parasites are crucial to the world’s ecosystems. Their extinction may effect entire food webs, perhaps even harming human health.
Parasites typically live in or on their hosts, but that does not protect them from climate change. Rising air temperatures can harm them. Ticks, for instance, risk baking in the heat as they wait in the grass for their next victim. Hookworm larvae require damp soil to survive before slipping into someone’s foot.
Some parasites won’t lose much in a warming world, the study found. For instance, thorny-headed worms are likely to be protected because their hosts, fish and birds, are common and widespread.
But other types, like fleas and tapeworms, may not be able to tolerate much change in temperature; many others infect only hosts that are facing extinction, as well.
In all, roughly 30 percent of parasitic species could disappear, Mr. Carlson concluded. The impact of climate change will be as great or greater for these species as for any others studied so far.
Mr. Carlson said climate change would do more than just drive some species extinct. Some parasites would move into new territory.
Deer ticks, for example, spread Lyme disease, and climate change models suggest they have a rosy future as they expand northward. “We’re not worried about them going extinct,” said Mr. Carlson.
Migrating parasites like these will arrive in ecosystems where other parasitic species are disappearing. With less competition, they may be able to wreak more havoc — and not just on animal hosts. Many human diseases are the result of parasites and pathogens jumping from animal species to our own.
“If parasites are keeping disease down in wildlife, they might also be indirectly keeping them down in humans,” Mr. Carlson said. “And we might lose that.”
PAUL FETTERS FOR THE SMITHSONIAN INSTITUTION
Specimens from the National Parasite Collection, which holds more than 20 million parasites. Though reviled, parasites play a significant role in maintaining the world’s ecosystems.