The last wolves in Yellowstone were killed in 1926. They were gone from Yellowstone for almost seventy years. Their absence had a number of direct effects, like creating the huge numbers of elk, mule deer, and pronghorns that crowd the meadows and hillsides and cause traffic jams along the roads. But it also had indirect effects.
For one thing, it screwed up the rivers and streams.
How, you may ask?
It goes like this: As the ungulates found themselves unthreatened, their population not only rose, but their eating habits changed. They began to spend a lot of time on the riverbanks, where the foliage was lush and savory.
This was a problem for the beavers.
In the early twentieth century, Northern Yellowstone was rife with beavers. Every stream and pond had its allotment of beavers and their dams, creating pools, slowing erosion, and generally shaping the riparian environment.
The beavers had a symbiotic relationship with the willows. The mature willows fed the beavers and provided the materials for their dams. In return, the beavers created a perfect shoreline ecosystem to grow more willows. Even their harvesting of mature willows cleared the way for the young willows to grow up.
Unfortunately, young willows are very tasty.
With the loss of the wolves, the ungulates began clearing away the young willows while the beavers were clearing away the mature willows. Pretty soon, there were almost no willows on the riverbanks. Not long after that, almost no beavers. And with the loss of the beaver dams, the streams opened up, draining away the water, causing erosion, and, as often as not, leaving bare, rocky beds inhospitable to lots of kinds of life.
The overpopulation of deer was recognized as a problem. So, in 1995, wolves were reintroduced to the northern Yellowstone. And, voila, the ungulate populations began to drop…a bit. More importantly, they stopped taking their lunch breaks on the open riverbanks. This gave a chance for the willows to return. Which they did…a bit.
Problem is that after seventy years, a new ecology had grown. The mix of riverside vegetation had changed and stabilized. Riverside water tables were low, so the willows had trouble getting to a height (over 2 meters) to survive the winters and discourage browsing ungulates. But, most importantly, the beaver population had cratered. Without the beaver dams, none of the other changes could be reversed, wolves or no wolves.
So the Park Service has reintroduced beavers. And in some areas, they are thriving. But not in the north, their old preferred area. It has changed too drastically to welcome them. In time, perhaps some hardy pioneer beavers will move north and start to reclaim their old home ground. Or perhaps we will discover that there is some other constraint we never thought about that we will have to try and overcome. Nature likes to surprise us.
Take, for instance, whale poop.
Baleen whales live largely on krill, tiny shrimp-like crustaceans. The Antarctic krill biomass alone is estimated to measure hundreds of millions of metric tons. A single whale can consume a colossal amount. So, like the situation with the wolves and the elk, you would assume that as we slaughtered the whales, the population of krill would have skyrocketed.
But it didn’t. Instead, it has dropped. Dramatically.
To call this counter-intuitive is to indulge in wild understatement. You kill off the predators that have been attacking a population and the populations falls? What the (expletive deleted)?
Okay, here’s one theory on what’s happening.
Krill live on phytoplankton. One of the major constraints to life in the oceans is a relative scarcity of iron. The krill need iron. The phytoplankton are full of iron. If the phytoplankton just dies, their carcasses drift down and are lost in the sea mud. However, if the krill eat them, the iron stays in circulation. But if the krill just dies, their carcasses, too, just drift down and the iron goes to the sea floor.
Enter the baleen whales. They take in vast amounts of krill, containing far more iron than the whales need. When the whales rise to the surface, they produce their own giant plumes of iron-rich whale poop. The phytoplankton feed on the whale poop, re-use the iron, and the cycle goes on. Baleen whales may thus be necessary to keep the iron in its biological circulation. So when the whales declined, so did the phytoplankton. And then so did the krill. Which has also led to a decline in animals that also live off krill, like penguins and squid.
Human beings spent many a long year killing whales for oil, or meat, or corset stays. We kept it up right into the 1970s. (A few countries are still at it. Ironically, one of the reasons that Japan claims for continuing their whale hunting is that fewer whales will obviously mean an increase in the krill population!)
But wait, there’s more. It’s not only the whales whose populations have declined. Other mammals like sea lions, seals, and sea otters have seen their numbers crash. How come?
The answer may be whale hunting again. One theory with some pretty good data suggests that while baleen whales are krill predators, they are also prey. In this case, for orcas. Historically, the orcas were major consumers of whales. There were so many whales that they supported a very large population of orcas. Then we started killing off their favorite entrees.
Not wanting to starve, the orcas switched their diet. Some occasional items of their cuisine, like sea lions, seals, and otters, changed to being the main dishes. It remains to be seen whether, as the whale populations slowly rebound, orcas will switch their preferences back. Just as it remains to be seen whether the krill and all the species that depend on them will rebound along with the whales.
In Glory Road, Robert Heinlein has one character say, “Disturbing a natural balance is a matter to be approached with fear and trembling – and a very versatile computer.”
A lesson we have yet to learn.