Even in large areas such as the Santa Susana Mountains and the Simi Hills, isolation could lead to the depletion of mountain lions and badgers within 200 years, according to Michael Soule of UC Santa Cruz, a conservation biologist who is a leading proponent of wildlife corridors.
But Simberloff, the Florida State biologist, is skeptical. He said the popularity of corridors is based more on emotion than reason.
"I know how to stop wildlife habitat degradation tomorrow. So do you. Stop development," Simberloff said.
But because that is impossible, he added, biologists have embraced the concept of corridors as a seemingly easy way to solve the vexing biological problems caused by development.
"It took off because it makes sense. It sounds like animals should move through corridors. It made people think there was an answer that might be feasible," Simberloff said. "Stopping development in California may not be feasible, but building corridors may be."
He said a proven and more practical alternative is to require developers to set aside large blocks of land as open space.
A recent paper published by the U.S. Fish and Wildlife Service also took a jaundiced view of the benefits claimed by corridor supporters.
"Corridors are an appealing Band-Aid remedy for wildlife management in landscapes that have already been fragmented by substantial development of natural resources," said the paper, published by the agency's National Ecology Research Center in Fort Collins, Colo. "Corridors may yet prove insignificant to the conservation of many wildlife species."
Edelman shrugs off skeptics by saying that development is occurring so rapidly that environmentalists can't wait for all of the scientific evidence to come in.
"You can't prove anything, so you have to be conservative. There's so much at stake," Edelman said.
In Ventura County and western Los Angeles County, Edelman envisions permanent links that would allow animals to roam from the Pacific Ocean to the nearby Los Padres and Angeles National forests.
Getting from one to the other isn't easy. Animals must cross as many as three major land masses: the Santa Monica Mountains, Simi Hills and Santa Susana Mountains.
Each is separated by one of the most effective human barriers to wildlife movement: the freeway.
The handful of freeway crossings that animals can use were built for other reasons, long before wildlife corridors became an issue.
One of these accidental crossings is a 15-foot-high concrete underpass at Santa Susana Pass, beneath the Simi Valley Freeway.
Originally built for the convenience of film crews at Corriganville, a former Western movie set, the tunnel is a key wildlife crossing between the Santa Susanas and Simi Hills.
Edelman spent a year studying animal tracks in the tunnel for a study he did of regional wildlife corridors. He recently revisited the tunnel, which is invisible from the roadway down a steep, overgrown embankment.
"Here's a raccoon. That's a coyote," he said, peering at indentations, hardened in dried mud beneath a spray-painted picture of a large marijuana cigarette and other graffiti.
In a layer of silt near one entrance, Edelman pointed out other faint impressions left by a passing baby bobcat, an opossum and a wood rat.
Edelman promotes the idea of a similar tunnel under the Ventura Freeway at Crummer Canyon, just east of the Ventura County line. But the cost could be about $5 million, according to an estimate Edelman received from a California Department of Transportation engineer.
"Things have been connected purely by chance, and society has woken up when there's still a chance," he said.
Edelman said the Corriganville tunnel demonstrates that a crossing can attract wildlife.
"I look at it like the 'Field of Dreams' scenario," he said. "If you build the field they'll come. If you create the habitat the animals will use it."
Edelman's agency, the conservancy, has made a multimillion-dollar commitment to wildlife corridors.
The state agency buys land that is later sold to parks agencies. Rorie Skei of the conservancy said creation of corridors "is one of the more important criteria" when the conservancy decides what property to purchase.
The desire to preserve a corridor between the Simi Hills and Santa Monica Mountains was one of the primary motivations behind the conservancy's proposed purchase of 7,437 acres on the Jordan Ranch from entertainer Bob Hope. The $19.5-million purchase, which was tied to the controversial Ahmanson Ranch development, stalled after negotiators and Hope failed to come to terms on the deal.
Preserving a key wildlife corridor was a primary motivation for the city of Simi Valley and the Rancho Simi Park and Recreation District, which spent more than $1 million to buy Corriganville, which lies on one side of the Simi Valley Freeway underpass.