Alternate Stable State Theory and Yellowstone’s Wolves
How a too-tidy story gets messy and why that’s still pretty ok
This is a transcript from a social media video, watch here if you like
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If you’ve ever been to Yellowstone, or watched a single documentary about it, or even watched a couple of episodes of Yogi Bear, or have ever eaten out of a pic a nic basket, you probably have heard about the miraculous recovery of streams in the greater ecosystem when wolves were reintroduced in 1995. Since then, elk were scared away from streams, the stream vegetation recovered, and beavers came back. All because of wolves.
You’ve heard this story a million times. Heck, you’ve even heard it from me. The story of trophic cascade in Yellowstone National Park. Well friends, I come to you, hat in hand, bald head exposed to god and everyone, to tell you the same thing I’ve had to say so many times: ecosystems are complicated things and in every way we should resist easy answers.
Trophic cascade, in a nutshell, says that removing top predators from a landscape results in prey proliferation, which in turn creates an imbalance in grazing. The assumption is that by reintroducing that predator, the imbalance can be reversed, just like that. I mean I just barely made a video about this regarding sea otters.
Well, darn it. I’m afraid this 20-year-plus study (https://esajournals.onlinelibrary.wiley.com/doi/10.1002/ecm.1598) calls that hypothesis into question. Now of course no science is ever settled, and if someone says it is they’re selling you something sketchy, but this is a pretty compelling study. And let’s just get this out of the way. by no means do I think this is an argument against wolf reintroduction.
Anyway
Starting in 2001, researchers identified plots to monitor and measured the willow heights year after year. The plots were either fenced-off, fenced-off with an artificial beaver dam, no fence with a beaver dam, and unaltered. The idea is that if wolf reintroduction alone was enough, even the unaltered plots would show regeneration of willows over 20 years. But those plots remained more or less unchanged. In the fenced plots with beaver dams, willows grew over three times as high as those without either. Fenced plots without dams and unfenced plots with dams both outcompeted the control group, though less than when both measures were implemented. That means that predators alone weren’t preventing enough browsing from elk for meaningful recovery. The most important factor was physically protecting the stream bank willows with fencing and raising the water table so roots could more readily access it.
Another aspect of the study that makes it interesting is that it took into account the expansion of both mountain lion and grizzly bear populations at the same time as the wolf reintroduction. This is a place with more than one capable apex predator. The difference is that cougars and grizzlies repopulated the area naturally. The study’s literature review found that in the Greater Yellowstone Ecosystem, each cougar killed double the elk than each wolf. According to the National Park Service, the northern range of the park has between 34 and 42 cougars. That’s compared to over 100 wolves. Those are some efficient kitties. Grizzly bears go after elk calves, and also seem to have a larger impact on elk populations than wolves do.
Now, the prevailing theory for why the ecosystem was and is in that degraded state in the first place still is the deliberate eradication of predators, the Yellowstone Visitor Center didn’t lie to you about that part. It’s still the overgrazing by elk. And it’s still the starving of beavers that resulted. Without dams the stream cut so far into the slopes that plants couldn’t access the water anymore and converted from willow to grassland. This is why predator reintroduction and protection is still vital to maintain already healthy ecosystems across the country.
Unfortunately, like many ecological problems, just putting that thing back where it came from or so help me does not seem to be the fix.
It kinda makes sense. Let’s say I were to just stop putting oil in my car. It would eventually lead to a catastrophic engine failure. Putting the oil in after the fact wouldn’t fix the parts that need complete rebuilding, right?
So the bad news is that, at least according to this study, the Yellowstone ecosystem probably won’t recover to the kind of state it was in the early 1900s when predators were killed off if we just leave it alone with the parts back in it. Not without some pretty drastic human intervention, which is generally contrary to current US National Park management philosophy.
The good news is that all the major pieces are coming back. Another positive thing is that it appears that the current state, though different, appears to be stable. This is called “alternate stable states theory.” Instead of thinking of ecosystems as places on an inevitable pathway to a certain “ideal” climax state, alternate stable states proposes that the same place can settle into different ecosystem types based on the current factors and stay that way unless something truly momentous comes along. This is something we’re all talking a lot about these days when confronting the challenges associated with climate change, by the way. We don’t talk as much about “restored” ecosystems. We talk about resilient ones.
And sometimes that’s ok, right? Maybe we’re all like ecosystems. Maybe something long ago was taken away from us and we’re now different people because of it. . But we’re still pretty neat. I think you’re neat, I mean. Even if there’s some other path you could have taken and you wonder how it would have gone. That’s resilience. You’re here and I’m glad. I hope you know that.