Mountain lions in Southern California are under growing pressure from a shrinking gene pool, fragmented by highways and urban sprawl that has left the cats' territories increasingly isolated from each other, a study published on Wednesday showed.

Analysis of DNA from about 350 mountain lions, or cougars, statewide revealed that those in the Santa Ana Mountains southeast of Los Angeles are only about half as genetically diverse as more robust populations in the Rockies.

The Santa Ana range is surrounded by an expanding population of about 20 million people. A corridor linking cougar territory there to a bigger range — and more lions — to the east is cut off by a 10-lane highway.