Are cougars the saviors of oaks?
Things in nature are knit together in some of the most
surprising ways.
A consequence of reintroducing wolves to Yellowstone National
Park is healthier stream sides.
Are cougars the saviors of oaks?
Things in nature are knit together in some of the most surprising ways.
A consequence of reintroducing wolves to Yellowstone National Park is healthier stream sides.
The return of wolves resulted in a reduction in the park’s elk herd. With fewer 1,000-pound herbivores loitering around creeks, riparian vegetation made a rapid comeback and the landscape changed to something closer to what it once was.
Now researchers claim that hunting and other human pressures that pushed cougars out of Yosemite Valley had similar consequences to the once-missing Yellowstone elk.
The sharp reduction in cougar numbers allowed Yosemite’s mule deer to multiply. As they browsed on young black oaks, the trees began to disappear and pines and fir trees moved in. Even the wild evening primrose grew rare, the victim of its nutritious roots.
Oregon State University researchers are the ones who connected the dots in Yosemite. According to an article in the San Francisco Chronicle, William Ripple and Robert Beschta believe the removal of an apex predator sends ripples through an entire ecosystem.
But Yosemite’s biologists are not yet sold.
“They’ve brought up a really complicated issue and an interesting theory, but it needs much more rigorous study,” said Nikki Nicholas, the parks chief of resource management.
Leslie Chow, a cougar specialist with the U.S. Geological Survey at Yosemite, said nobody knows how many of the reclusive cats are left in the park. With natural ranges of up to 100 or more square miles per cat, there may have been 20 to 50 in the park in the 1920s, when hunters were paid to kill them off.
More recent DNA studies reveal there are now some 25 cougars still in the park.
The Oregon State researchers call the kind of chain reaction they’re studying a “trophic cascade,” in which little known connections between organisms reveal themselves.
There may be something else at work, however, and again, humans have a hand in it.
Ripple called it “the ecology of fear.” When cougars shun human presence, deer may tend to bunch up closer to where the people are, just as they seem to in Yosemite Valley. That may lead to changes in plant life.
Certainly, hunters and some wildlife observers locally believe they are seeing their own trophic cascade.
When sport hunting of cougars was outlawed, they believe deer numbers rapidly declined. They point to increased reports of encounters between humans and cougars as well.
That may well be because there are just more people in once-wild areas. The point is that nobody really knows. That’s exactly what makes studies like the one being conducted in Yosemite so compelling.
There’s a lot we understand about the world around us. But there’s a lot more to learn.
