VOA英语2010年-Human Health Depends on Biodiversity（在线收听）

There's a good reason why people should be concerned about having a healthy environment containing lots of animal and plant species. A new study says the loss of biodiversity may make humans more vulnerable to infectious diseases.

Biodiversity is one of the ways to measure the health of an eco-system.  And the healthier an eco-system is, the better off we are. That's because animals, plants and even microbes can act as a buffer between people and pathogens.

Associate Professor Felicia Keesing, an ecologist at Bard College in Annandale, New York, is the lead author of the study.

"Biodiversity is the diversity of genes, species and eco-systems that occupy the earth. Most of the time when we talk about biodiversity, we mean the diversity of species," she says.

Keesing says the study adds a new reason to protect the environment.

"People have always recognized that there's some sort of esthetic value in having all of these different creatures living on earth with us. Many people feel that there's an ethical responsibility to protect them. But in the last couple of decades, scientists have begun to document ways in which biodiversity is actually providing services to us. Such services become practical reasons for protecting biodiversity as well," she says.

It's long been known that biodiversity helps provide clean water, cycles nutrients through the eco-system, and absorbs carbon from the atmosphere. But Keesing says the fact that biodiversity protects humans from disease is a compelling reason for conservation.

Sucking up pathogens

Keesing says, "What we've seen over and over again in different studies that we describe in our paper is that in diverse systems the species that are present either reduce the number of disease bearing organisms by competing with them. Or they suck up pathogens, sort of vacuum up pathogens, and then don't transmit them again."

That protection suffers as biodiversity is lost. Keesing says one example is Lyme Disease, which is a common tick-borne bacterial illness in the United States.

"If you have a low diversity system, the species that are present always include white footed mice. And white footed mice are very, very good at transmitting the Lyme bacterium back out so that humans are at risk," she says.

Eco-systems under attack

Biodiversity faces many threats all over the world. The biggest, she says, is land conversion.

"We're destroying habitats," she says, "So there are fewer places for organisms to live. But there are also a lot of other threats. The key ones are also climate change. So as the climate changes species are struggling and in some cases going extinct because they can't adapt quickly enough – or they have nowhere to go that has the appropriate environmental conditions."

Other threats to biodiversity include the spread of invasive species of plants and animals, as well as overhunting or overharvesting of species.

"In many ways, the biggest threat is that all of these things are happening at the same time and interacting with each other," she says.

Keesing rejects the idea that the loss of biodiversity is simply a matter of survival of the fittest, with humans being the most fit.

"Our survival," she says, "is actually linked to the survival of these other species. So, neither our short term nor our long term survival prospects are increased because we're destroying other species."

Scientists are also considering what a loss of biodiversity means for such diseases as Ebola in Africa. In other words, could it mean the disease could become more common and spread to new areas if there's a weak biodiversity buffer?

The Bard College associate professor says the effects of biodiversity loss are so clear, there's no reason to delay protecting the Earth's eco-systems.