Interstate 15 is big. It stretches across 10 lanes through the Santa Ana and Santa Monica mountains. It also keeps puma populations away from each other.
A study of 354 pumas in California by scientists from UC Davis School of Veterinary Medicine found that pumas in Santa Ana and Santa Monica had significantly lower genetic diversity than pumas in other parts of the state. This lack of genetic diversity was caused by human developments like the I-15. Over time, pumas have been forced to inbreed and their genetic diversity has plummeted.
"The lack of diversity is likely to cause serious problems within the next 20-50 years," said Dr. Paul Beier, of North Arizona University, who works on the science-based design of wildlife corridors. "We know this because the Florida panther (same species as puma) also suffered lack of genetic diversity in the 1980s and 1990s that caused serious heart defects, sterility in many males, and susceptibility to infections."
During the study, one puma got lucky and managed to cross Highway 101. He re-invigorated some of the genetic diversity among the pumas he encountered on the other side. But this is rare, especially as human populations around San Diego and Los Angeles grow and continue to develop the landscape.
Preventing a lack of genetic diversity in land-bound species will require urban planning that takes animal movements into consideration. One solution is to leave large pieces of land undeveloped. Another is to create crossing structures so animals can get past highways and railways with no danger of being struck by a moving vehicle.
"I suspect that lack of genetic diversity is a problem only for a handful of populations today, and that most puma populations are genetically healthy," added Beier. "But this could become a problem in more places as human footprint on the landscape grows."