If you visit Zion National Park today, you’re likely to see something like this, or this,
and most definitely this. But what you’re not likely to see, is this [insert picture
of mountain lion], a mountain lion. You might call it a cougar, a catamount, a panther,
or a puma, depending on where you live. But, no matter what you call it, these are all
the same species: Felis concolor, the world’s fourth largest cat.
Pound for pound, mountain lions are one of the most lethal felines on the planet. They’ve
been known to take down bull moose, which can be almost 10 times their size. They’re
primarily ambush predators, relying on stealth, explosive movement, and ferociously powerful
jaws to deliver suffocating bites to the necks of their unwitting prey.
And like most of their large carnivore brethren, mountain lions have been driven out of most
of their historic range. As solitary hunters, they require large amounts of uninterrupted
habitat to support themselves, something completely at odds with current human development patterns.
And so, mountain lions today only inhabit a small fraction of that historic range.
One of the areas cougars do still inhabit though, is Zion National Park - except in
Zion Canyon. The heart and soul of Zion, the place that the vast majority of visitors come
to see, is conspicuously devoid of mountain lions. The home of Angel’s Landing, the
Narrows, and the Great White Throne hasn’t been home to mountain lions since the 1940s,
and the reason for that is actually pretty simple: there’s too many people.
Mountain lions are generally pretty skittish animals, and will avoid humans if at all possible.
The hustle and bustle has driven them out of Zion Canyon in favor of the park’s more
isolated and less developed reaches.
We can trace the beginnings of the cougars’ retreat back to the early days of Zion itself.
The park was officially designated in 1918, but the park underwent a decade of development
between 1924 and 1934 which greatly improved its recreation and tourism infrastructure.
Most of this development occurred in Zion Canyon. The new roads, highways, trails, and
tunnels vastly improved the canyon’s visitor experience, making one of America’s great
natural cathedrals more accessible than ever. In that decade, Zion’s visitation grew by
an astonishing 719%!
But as we now know, that increase in visitation led to a decrease in mountain lion numbers
in Zion Canyon. As early as 1939, park biologists J.S. Dixon and E.L Sumner observed that “the
presence of these hundreds of human visitors tended to drive out the cougars, which are
the chief natural enemies of the deer.”
Their report foreshadowed more than just the retreat of mountain lions into Zion’s backcountry.
As we’ve learned in previous videos, (which I’ll link down below), when you remove a
top level predator from an ecosystem, ecological catastrophe tends to follow.
With mountain lions out of the picture, Zion’s mule deer were free to roam and graze in the
bottom of the canyon. They quickly consumed most of the Virgin River’s streamside vegetation,
including the all too familiar cottonwood trees. The mule deer population soon exploded,
and by the 1940s the situation had become so dire that park officials resorted to shipping
deer out of the park in an effort to keep their numbers under control.
It was at this point that the consequences of the cougar’s removal became clear. After
all, similar observations had been made in Yellowstone shortly after its wolves were
exterminated. But just like Yellowstone, it would take decades to uncover the full extent
of the damage.
In 2005, the same researchers who uncovered Yellowstone’s wolf cascade, Bill Ripple
and Bob Beschta, would come to Zion to solve another ecological mystery - and this time
cougars were the culprit. What they would uncover is altogether remarkable and unsurprising.
Unsurprising in the sense that park officials and biologists already had a sense that cougar
removal was negatively impacting Zion Canyon’s riparian ecosystem. But what Ripple and Beschta
found that was truly remarkable, was the extent of the impact the cougar’s removal had on
Zion Canyon.
For their investigation, Ripple and Beschta compared two different areas in Zion National
Park: Zion Canyon and the adjacent North Creek Canyon just 9 miles away. These two canyons
were virtually the same: they had the same geology, climate, and vegetation. The only
difference was - North Creek still had cougars. It wasn’t subject to the same development
pressures of Zion Canyon and it remained relatively remote and quiet - a perfect environment for
cougars. And so, these two canyons provided the perfect setting to test what happened
to an ecosystem when cougars were removed.
The impacts to Zion Canyon were well documented at this point. The removal of mountain lions
had triggered an irruption of mule deer, which ate their way through the fragile streamside
plants and led to considerable erosion along the Virgin River.
But in North Creek, Ripple and Beschta found a virtual paradise. Not only were the cottonwoods
growing full and healthy, but the stream banks of North Creek were fully intact. Because
the stream banks were stable, native wildflowers like Cardinal Flower and Aster flourished.
These flowers, in turn, provided habitat for a whole host of butterfly species, including
Swallowtails, Sulphurs, Blues, Satyrs, and Monarchs. Five times as many butterfly species
were found in North Creek as Zion Canyon. Likewise, all those butterflies meant a drastic
increase in lizards, who ate the butterflies and lived among the streamside shrubs. Amphibians
abounded as well. Red-spotted toads and canyon tree frogs hopped merrily along the lush riverbanks,
appearing in numbers up to two hundred times greater than their neighbors over in Zion
Canyon.
The stability of North Creek’s banks also provided homes to desert fish. In Zion Canyon,
where the lack of plant life caused the river to run swift and deep, it was nearly impossible
for small aquatic life to survive. But North Creek’s calm waters formed pools and shallow
channels, perfect habitat for fish like the speckled dace and flannelmouth sucker.
This was a true trophic cascade. Just like in Yellowstone, Ripple and Beschta had found
definitive evidence that the removal of a top-level predator had profound consequences
for the ecosystem at large. In Yellowstone, the removal of wolves led to an explosion
of elk which devastated its streamside ecosystems. And now, in Zion, the removal of mountain
lions had led to similar devastation with its mule deer.
The case was now stronger than ever that predators had an undeniable role in the protection and
preservation of the world’s ecosystems. Here were two completely different animals
in two completely different habitats impacting their ecosystems in remarkably similar ways.
With top level predators removed, the ecosystems of Yellowstone and Zion had crumbled. The
same can be said of Isle Royale with its wolves. Numerous other studies have only bolstered
the evidence in favor of the Green World Hypothesis.
And, it’s clear to me at least, that the Green World Hypothesis provides a ringing
endorsement of protected places. It’s no coincidence that the three stories I’ve
told about it all take place in National Parks. Parks, forests, refuges - these are some of
the last remaining areas where we see these sort of ecological relationships take place.
They’re some of the last places where large predators roam free, where the sort of ecological
balance they provide remains intact. Predators and protected places, go hand in hand. We
should all look to the Green World Hypothesis, with all of its lessons and implications,
as a shining example of what can happen when we protect and preserve wild places.
I hope you enjoyed this whirlwind tour through predators in our national parks. If you missed
the first two installments, feel free to check those out. I’ll link to them in the description
below. And, if you’ve got any other stories of predators in National Parks or protected
areas, leave them down in the comments - I’d love to hear about them, and possibly tell
them on the channel.
And as always, if you want to learn more about the world’s protected places, don’t forget
to like this video and subscribe to the channel. Thank you so much for watching, goodbye.