A recent article in “Discover” magazine has added new data to our evolving understanding of the impact of reintroduced wolves in the Northern Rockies. A biologist studying the Yellowstone National Park’s northern elk herd concluded that the introduction of lake trout into Yellowstone Lake may be a factor in that herd’s decline.
If that conclusion led to a spit take of your morning coffee, I get it. And if the coffee spill put you in a surly mood you may be asking, “Just how far off the deep end are these socialist, anti-hunting, wolf-loving biologists willing to go to avoid admitting the obvious?”
Wolves eat elk. End of story. Right?
Well, maybe. Lake trout may seem entirely unrelated to elk, but the more I learn about ecosystems and wildlife, the more I understand how changes in one part of a food chain can cause unexpected consequences somewhere else. Biologists call this phenomena trophic cascades.
Here’s a condensed version of how fish may have contributed to the decline of elk: Non-native lake trout killed or displaced native cutthroat in Yellowstone Lake. Lake trout spawn in the lake, often in deep water where they are unavailable for predators such as grizzly bears. Park grizzlies, accustomed to fattening up in the spring on stream-spawning cutthroat, had to find a new food source. It turns out lumbering bears are pretty efficient predators on elk calves. So that’s where some of the bruins turned when cutthroat runs collapsed.
One study showed bears contributed far more to elk calf mortality than wolves. So finally, we have are smoking gun, right? It’s big, bad bears.
Again, the answer is maybe. I’ve learned something else about trophic cascades: true smoking guns are rare in nature.
Bear predation alone doesn’t seem to be enough to cause the elk decline. And in my mind it’s simply foolish to suggest wolves have nothing to do with the northern herd’s reduced numbers. I hate to restate the obvious, but wolves do eat elk. There is going to be some impact from that, and there will also be some indirect impact on elk populations simply because elk in the presence of wolves have to behave differently.
One of the changes we expected when wolves returned to Yellowstone was that the elk — jarred from the stupor of their predator-free lifestyle — would have to get back on the move. Elk would have to be more cautious, and could no longer afford to camp out in the river bottoms feasting on nutritious willow. Not only would wolves flourish, the story suggested, but so would species such as beaver and songbirds that relied on willow for food and habitat.
But the same researcher, Arthur Middleton, who’s work suggested the lake trout/elk decline link, is also skeptical about wolves serving as some sort of apex-predator superhero, able to restore damaged riparian areas by its mere presence on the landscape. It turns out decades of elk over grazing may have damaged these streams beyond recovery and are lost forever.
Or, again, maybe nature is more complex than we assume. It could be that returning wolves to Yellowstone was just the first step in restoring those riparian ecosystems. The next step may require active restoration to recreate the kind of marshy habitat beaver and willow need to thrive. This kind of restoration is best accomplished with heavy equipment.
I suspect the mere thought of big yellow Caterpillars mucking around in nature will be too much for some to accept.
As for the decline of elk, I’m going with the multiple factor theory. Yes, bears and wolves are eating elk calves. But human hunters take a share as well. And the elk decline has coincided with a period of extended drought.
You may want to put down your coffee for this, but guess what? If there’s less grass you’ll grow fewer elk. That’s one smoking gun in this complex tale I’m pretty sure is right.