The South Coast ecoregion is a hot spot for biodiversity in the United Statesit is also considered the most threatened.
For mountain lions in the Santa Monica Mountains a single underpass at Liberty Canyon is the lions' best chance to cross the 101 freeway for many miles in either direction. It is the only area with undeveloped wildlands on both sidesthe Santa Monica Mountains on the south side of the freeway and the Simi Hills wildlands on the north.
The canyon causes the land to dip slightly providing a hundred-foot (30-meter) stretch where the 101 rises more than eight feet (2.5 meters) above the ground and offers sheltered passage across.
But the nearest core population of mountain lions is in Los Padres National Forest, more than 22 miles (35 kilometers) away from the Santa Monica Hills. To provide a safe route all the way there would require several other linkages via the Santa Susana Mountains.
"The truth is it would have been nice if [the linkages were] 30 yrs ago, because a lot of the development along the freeway  has already happened," says Riley. "There are actually precious few places unfortunately that are left where we can try to maintain some connection."
Lions Study Freeway, Researchers Encouraged by Successful Corridors
The Liberty Canyon underpass is just about a hundred feet (30 meters) long. It seems a long shot that the mountain lions would use this bridge.
But late last year, according to the satellite tracking data, P2 sat on a hillside overlooking the 101 freeway for about three hours. She would have seen the freeway, the green grass on the other side, and just maybe a way across.
Ideally the mountain lions would use the Liberty Canyon underpass to travel in and out of the Santa Monica Mountains, but so far the biologist have not seen this happen.
Throughout the Santa Monica Mountain Recreational Area, Riley and York have about 20 traps to capture other mountain lions for tag and release.
A successful example of a wilderness corridor can be seen not far from San Diego, on the eight-lane 91 freewayCoal Canyon is a model for getting animals from point A to B.
"[Coal Canyon] used to be asphalt, this whole area used to be an underpass," says Penrod. "I mean people would exit the freeway and come under here." More than a thousand homes along with gas stations and restaurants were slated for development at the Coal Canyon exit. But those plans were abolished when scientists realized that a mountain lion they had been tracking, called M6, was using the underpass to cross the freeway and move between suitable parts of his habitat.
The underpass is now a wildlife corridor for mountain lions and many other animals and is currently being restored to its natural state.
Isolated Reserves, Sick Panthers
Now other sites are being watched closely too.
At the Santa Margarita Ecological Reserve, a seven square mile (18 square kilometer) link between the Palomar and Santa Ana Mountains, remote cameras track the movements of coyotes and birds and audio sensors detect bats.
"Wilderness corridors are necessary because we live in a human dominated landscape," says Paul Beier, a conservation ecologist at the Northern Arizona University in Flagstaff. "Although we have conserved significant areas, even the largest parks are too small to maintain independent populations of large carnivores like pumas, wolves, and grizzlies."
For example, the Grand Canyon National Park can hold about 20 mountain lions but if the park was isolated, that would spell extinction for those animals, Beier explains.
Researchers have found that isolated parks and nature reserves function like islands. Without animals coming in and out, animals inbreedcausing the gene pool to stagnate. The small, inbred population is more susceptible to decline via disease and natural disaster.
In Florida, for example, mountain lions, or panthers as they are known locally, became isolated over the last century till less than 50 breeding pairs remained.
"The population was very susceptible to infectionmany panthers had heart defects and some males were sterile," says Beier. The situation has gotten healthier since 1995, when a small group of animals, introduced from Texas, invigorated the Florida population.
In the Santa Monica Mountains researchers feel the pressure to move fast.
"It's not too late now but we, in Southern California, we have probably about ten years to secure these landscape level connections or they will be gone, and it will probably be forever," says Penrod.
National Geographic Today, 7 p.m. ET/PT in the United States, is a daily news journal available only on the National Geographic Channel. Click here to learn more about it.
Got a high-speed connection? Watch National Geographic Today in streaming video.
SOURCES AND RELATED WEB SITES