We've written a fair amount here at Rewild about the plight of pumas in the Santa Monica Mountains, cut off from their fellow lions by freeways to and from the San Fernando Valley. Without an easy way to meet and mate with pumas elsewhere, lions in the Santa Monicas are inbreeding, and that's bad for the cats' long-term survival.
And that problem isn't just limited to the Santa Monica Mountains. A study shows that the Santa Ana Mountains have become a similar isolated island for pumas that live there, cut off from their neighbors in the nearby Peninsular Ranges by increasing human development.
The two puma populations, once separated by just 15 or 20 miles of easily navigable foothills near Temecula, are now quite distinct in their genetic makeup -- and the study's authors suggest that much of the reason may be the 10 lanes of high-speed freeway known as Interstate 15.
The study, published recently in the journal Public Library of Science, was conducted by Holly Ernest, T. Winston Vickers, Michael Buchalski, and Walter Boyce of UC Davis, along with Scott Morrison from The Nature Conservancy.
The researchers collected DNA from 97 pumas in in San Diego, Orange, Riverside, and San Bernardino counties, either when the cats were captured for radio telemetry studies or in cases when individual pumas were shot due to livestock depredation or public safety reasons. 42 of the samples were collected in the Santa Ana Mountains, and the remainder in the Peninsular Ranges to the east. All the samples were collected between 2001 and 2012.
Study and comparison of different genetic markers in the samples confirmed that, as long suspected, the pumas in the Santa Ana Mountains have been inbreeding for a long time. Of the 42 Santa Ana pumas sampled, just one, dubbed M86 (with the M standing for "male"), had genes characteristic of the Peninsular puma population. He had apparently sired four kittens in the Santa Anas, each of which had a partial complement of Peninsular genes.
Aside from M86's progeny, none of the other mountain lions in the Santa Ana samples showed evidence of having Peninsular pumas in their recent ancestry. The study's authors calculated the length of separation necessary to generate that marked a divergence between two geographically close populations of pumas, and figured that the genetic bottleneck for Santa Ana Mountains pumas started between 40 and 80 years ago.
It was about 40 years ago, of course, that the era of freeway building in Southern California was at its peak.
"It is likely that the potential for connectivity between the Santa Ana Mountains and the Peninsular Range-East region will continue to be eroded by ongoing increases in traffic volumes on I-15," write the authors, "and conversion of unconserved lands along the I-15 corridor by development and agriculture."
"These findings raise concerns about the current status of the Santa Ana Mountains puma population, and the longer-term outlook for pumas across Southern California," the authors conclude. "Indeed, the Santa Ana Mountains pumas may well serve as harbingers of potential consequences throughout California and the western United States if more attention is not paid to maintaining connectivity for wildlife as development progresses."