- The mountain lion population in the Santa Monica Mountains, a coastal range outside of Los Angeles in Southern California, is very small, numbering just an estimated 15 individuals.
- Most crucially, they are isolated from other mountain lion populations, as their range is hemmed in by large freeways, agricultural operations, and the Pacific Ocean.
- This has led to low genetic diversity amongst the Santa Monica mountain lions — and that could spell the population’s doom, according to a new study published in the Proceedings of the Royal Society B last week.
The mountain lion population in the Santa Monica Mountains, a coastal range outside of Los Angeles in Southern California, is very small, numbering just an estimated 15 individuals. Most crucially, they are isolated from other mountain lion populations, as their range is hemmed in by large freeways, agricultural operations, and the Pacific Ocean.
Because of these barriers, the Santa Monica mountain lions must interbreed with each other, as new lions can’t access their range. This has led to low genetic diversity amongst the Santa Monica mountain lions — and that could spell the population’s doom, according to a new study published in the Proceedings of the Royal Society B last week.
In order to determine how inbreeding will impact the mountain lion population, a team of scientists led by John Benson, a researcher at UCLA’s La Kretz Center for California Conservation, used a theoretical model called the “extinction vortex.” The model is able to predict the extinction risk of small, isolated populations by accounting for interactions between demographic, environmental, and genetic factors.
With any population that small, the impacts of random variation in survival and reproduction rates are magnified — a bad year or two in terms of survival rate can lead to the collapse of the population, in other words. But the Santa Monica mountain lions exhibit fairly strong survival and reproduction rates, according to the study.
Thus the model the researchers used predicted stable median population growth and a mere 15 percent chance of the Santa Monica mountain lions going extinct in the next 50 years — but only when inbreeding wasn’t factored in. Breeding among close relatives eventually starts to compromise survival and reproduction rates, which is called “inbreeding depression.”
“When we reduced demographic parameters proportional to reductions documented in another wild population of mountain lions that experienced inbreeding depression,” Benson and his co-authors write in the study, “extinction probability rose to 99.7%.”
That’s a nearly 100 percent chance the Santa Monica Mountains’ population of mountain lions will go extinct in the next half-century if something isn’t done.
Luckily for the mountain lions, plans are already in motion that could save them from inbreeding themselves to extinction. According to Southern California Public Radio, a $60-million wildlife crossing over the 101 freeway is currently in the final design phase. The crossing would link the Santa Monica mountain lions with populations in the Simi Hills and Santa Susana Mountains.
“It wouldn’t take a lot of new mountain lions entering the population to make a big difference, both demographically and genetically,” Benson said in an interview with Southern California Public Radio. “If we were even able to get one new mountain lion every two years or, even every four years, it would considerably lower extinction probability.”
The wildlife crossing is a far better solution than, say, introducing new mountain lions into the Santa Monica Mountains, Benson said, because it will also benefit other species that are isolated in the mountain range, such as bobcats and coyotes.
Benson and his co-authors said that their study provided empirical evidence for the central tenet of the extinction vortex model, because their results showed that genetic and demographic factors greatly increased the mountain lions’ chances of dying out. “Our modelling approach realistically integrates demographic and genetic data to provide a comprehensive assessment of factors threatening small populations,” the team write in the study.
But their results might be applicable on a broader scale in more ways than one, Benson said.
“We’ve got the largest cat in North America persisting in the second largest city in the US. That’s pretty unique,” he said. “What we’ve been thinking is: if we can conserve mountain lions, the top predator in the Santa Monicas, then we can probably do it anywhere. Because it would be a model of large carnivore conservation in a highly, highly fragmented human-dominated landscape just around Los Angeles.”
- Benson, J. F., Mahoney, P. J., Sikich, J. A., Serieys, L. E., Pollinger, J. P., Ernest, H. B., & Riley, S. P. (2016). Interactions between demography, genetics, and landscape connectivity increase extinction probability for a small population of large carnivores in a major metropolitan area. Proc. R. Soc. B. doi:10.1098/rspb.2016.0957