California highways make for meaner (and fewer) mountain lions


A mountain lion hunts in the Santa Monica Mountains. (National Park Service)

When habitats are divided, so are animal populations. But unlike natural divisions like oceans and mountains, human-made barriers — major highways, for example — can spring up so suddenly that the effects are dramatic and devastating.

The wild mountain lion population in the Santa Monica Mountains (located within Greater Los Angeles) has been totally isolated by urban growth, and the 101 freeway in particular. A small population persists, but a new study in Current Biology paints a sad picture of its future.

Kittens are being born, but the population lacks genetic diversity. (National Park Service)
Kittens are being born, but the population lacks genetic diversity. (National Park Service)

For starters, they're cramped. Science Magazine reports  that the predators typically need about 1,100 square kilometers of space to support themselves, and the Santa Monica Mountains only provide 660 these days. And unfortunately, that's not the worst of it.

The top cat in the area, referred to as P1, monopolized females (as top cats are wont to do) and probably fathered all of the new lions born for some years. Typically, about 75 percent of young lions (all of the males, and half of the females) would leave the community to go find their own mates — but in the case of P1's rivals, there was no room. One of P1's sons managed to escape by crossing an interstate, but had nowhere to go but a smaller patch of land with no females.

Meanwhile, P1 exhibited unusually aggressive behavior, killing a son, a daughter, and (most bizarrely) a mate. He also bred with at least one of his daughters.

A hungry kitten in the Santa Monica Mountains (National Park Service)
A hungry kitten in the Santa Monica Mountains (National Park Service)

That level of inbreeding marks a downward turn in the genetic diversity of a species, and it's especially troublesome when the patriarch whose genes are getting re-hashed seems unusually violent.

In 2008, another mountain lion called P12 managed to cross into the territory, and has fathered eight offspring since then. But he's already mated with at least one of his daughters, too. If the California Department of Transportation doesn't create a tunnel or overpass suitable for mountain lion crossing, the researchers told Science Magazine, cramped quarters and inbreeding could make the population's demise inevitable.

Rachel Feltman runs The Post's Speaking of Science blog.
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Rachel Feltman · August 15