Turf wars: swelling human populations are crowding out other species.

It's not just in places like India or Zimbabwe that endangered plant and animal species are battling it out with growing numbers of people for the few remaining parcels of habitat. In the United States, too, population growth is the single greatest threat to endangered species. Every day, huge tracts of land are being gobbled up for new highways, subdivisons, office buildings and strip malls to accommodate a growing human population.

What's going on here? Didn't the U.S. already achieve population stabilization years ago? Well, no. Although it has maintained a low growth rate of 1.2 percent for the past 50 years (with a current fertility rate of 2.0, compared with 6.1 in sub-Saharan Africa), the country is still growing by three million people each year. In fact, the U.S. population has nearly doubled in the baby boomers' lifetime - from 150 million in 1950 to 267 million in 1997.

"Considering that the majority of the estimated 30,000 plant and animal species in the U.S. live near coasts where more than 50 percent of the human population also resides, massive habitat destruction is inevitable," says Anne Elizabeth Beale, deputy director of the Washington, D.C.-based group Population-Environment Balance. "And given our current growth rate, the rate of species extinction in the U.S. will increase dramatically unless we are able to achieve U.S. population stabilization." Five hundred species are already known to have vanished forever in the U.S.; at least 700 are endangered or threatened, and 9,000 are at risk of extinction.

The number of grizzly bears in the western U.S. was at one time estimated to be 100,000. Today, fewer than 1,000 remain, restricted to the mountainous areas of Wyoming, Montana, Idaho and Washington. In 1990, 65 of the remaining 300 Key deer in the U.S. were hit and killed by U.S. drivers on roads that run throughout the deer's habitat. One of the leading causes of death of the endangered manatee is being hit by drivers of recreational boats.

Not surprisingly, the places we love best - fast-growing spots like Southern California and Florida - are also "hot spots" for endangered species. A recent study by Princeton University scientists and Environmental Defense Fund senior ecologist David Wilcove found that the greatest concentrations of endangered species are in Southern California, Hawaii, southern Appalachia and the Southeastern coastal states, especially Florida. "They're all unique biological regions," says Wilcove, "and that's what makes the species so vulnerable. They have nowhere to go."

San Diego is a prime example of how the "livable city" reputation can be a virtual death knell for other species. People flocked there in the 1980s for the near-perfect climate and scenery that slopes gently from coastline to mountains to desert. Subdivisions with names like Rancho Mirage sprung up overnight. Massive paving of land threatened endemic habitats such as coastal sage scrub and the last 2,000 acres of Southern maritime chaparral left in the world. Today an estimated 200 species are at risk.

Now San Diego may also have a solution. After more than a decade of fighting, developers and environmentalists have worked together on the deal that Interior Secretary Bruce Babbitt has called "the jewel of habitat conservation plans." It will create a 172,000-acre preserve in the most heavily urbanized, southwestern corner of the county, and protect 85 species. But some environmentalists argue that, like many habitat conservation plans (HCPs), the San Diego plan gives away land that was better protected under the Endangered Species Act.

Austin, Texas is another fast-growing Sunbelt city where population pressures have threatened the habitat of endangered species. Once a sleepy university town and state capital, Austin's population passed the one million mark in 1995, with 100 new people arriving every day. In the 1990s, development in the Balcones Canyonlands was threatening the habitat of the golden-cheeked warbler and the black-capped vireo, migratory songbirds who were making music in the Texas Hill Country long before Willie Nelson or Jimmie Dale Gilmore arrived on the scene.

To protect these embattled creatures, environmentalists have spent the past six years hashing out a conservation plan that finally got Fish and Wildlife Service approval as the Balcones Canyonlands Preserve (BCP) in 1996. But like many HCPs, the Austin plan has had funding problems. "The plan has been stalled for the past year and a half because there hasn't been sufficient revenue," says Stephen Beers, conservation chair of the Austin Sierra Club. "It's only now just gotten back on track."

While HCPs have potential as stopgap measures, the only viable long-term solution is human population stabilization or reduction. Population-Environment Balance advocates a reduction in both fertility rates and immigration.

Endangered species advocates also say we need to stop wasteful land-use practices in favor of denser development and stricter zoning codes like the ones being tried in Portland and Boulder. And, they say, consumption levels need to be dramatically reduced. The environmental impact of a child born in this country is 300 times that of Uganda or Laos, according to population experts Paul and Anne Ehrlich.

"We are the archetype of a gigantic, overpopulated, overconsuming rich nation," say the Ehrlichs, "one that many ill-informed decision makers in poor nations would like to emulate. Unless we demonstrate by example that we understand the horrible mistakes made on our way to overdevelopment...there seems little hope for the persistence of civilization." CONTACT: Population-Environment Balance, 1325 G Street NW, Suite 1003, Washington, DC 20005/ [phone].