The Interlocking Nature of Ecosystems

Junction Butte Pack Wolves – Lamar Valley – Yellowstone photography by Heidi Pinkerton,

In July 2020, National Geographic writer Christine Peterson described the impact of 25 years of the reintroduction of gray wolves to Yellowstone National Park. For 70 years, the wolves had been eradicated in the park, and most of the country, partly because government wildlife policy was to kill animal predators.

Yet as Ecolutionaries know, interlocking pieces in an ecosystem tend to bring resiliency.

Reintroducing wolves led to a strengthening of elk herds and the return to health of some trees and animals. Mainly, as Peterson reported, this was because elks were no longer starving to death, cow elk were more plentiful for reproduction, and overpopulated herds thinned, allowing tree growth to improve habitat for other birds and animals.

Why did this happen?

With normal rain and snow, cow elk were the easiest to hunt and that is what wolves targeted. But in dry years, giant bull elks were in a weakened state in the winter and burned off too many calories fighting with each other over mates, making them an easier target.
“As adaptable, intelligent predators, wolves have learned to recognize these conditions, and they would rather kill an undernourished 750-pound bull versus a 450-pound cow,” Peterson wrote. “So by targeting bulls during years of scarce food, they give the cows a chance to reproduce, thus keeping the population afloat.”

The thinning of overpopulated elk herds allowed some willow and aspen groves to return and create better habitat for songbirds and beavers. 

How did they figure this out?

Scientists analyzed more than a thousand dead elk in Yellowstone — through Wyoming, Montana, and Idaho — over 20 years. The scientists each winter “tracked three wolf packs, locating every elk kill the wolves made; recording the dead animal’s age and sex; and removing a bone marrow sample, which determined the elk’s physical condition before death. The team then used satellite data to derive how much plant life was available for elk to eat each year, an amount dependent on snowmelt and rainfall.”

The last known Yellowstone wolf pack was killed in 1926. Bears and lions also were greatly diminished by government policy. As a result, elk populations skyrocketed, but were not as resilient as they are now.
Between 1995 and 1997, wildlife officials reintroduced 41 wolves to Yellowstone.

In the winter of 2010 to 2011, scientists found that elk fared relatively well during abnormally deep snow and cold temperatures, compared with mass deaths during similar winters in the 1980s and 1990s.
Starvation, scientists told Peterson, is a sign of a weak system. In a healthier society, more evolved systems are better adapted to changing conditions.

Related Story

excerpted from The Guardian,January 25, 2020

“By 1926, the last wolf pack had been killed in Yellowstone by park employees as part of the policy of the time to eliminate all predators.They were mythologized as a danger to humans, a menace to the ranchers settling the west and competition for big-game hunters. That mythology still persists to this day, although wolves very rarely attack people, especially compared with cougars and bears. Wolves kill 0.2% to 0.3% of available livestock.

“In the 70 years of the wolves’ absence, the entire Yellowstone ecosystem had fallen out of balance. Coyotes ran rampant, and the elk population exploded, overgrazing willows and aspens. Without those trees, songbirds began to decline, beavers could no longer build their dams and riverbanks started to erode. Without beaver dams and the shade from trees and other plants, water temperatures were too high for cold-water fish.

“Scientists always knew that as the top predator, wolves were the missing piece in this ecosystem. But they were astonished at how quickly their return stimulated a transformation. The elk and deer populations started responding immediately.

“Within about 10 years, willows rebounded. In 20, the aspen began flourishing. Riverbanks stabilized. Songbirds returned as did beavers, eagles, foxes and badgers. “And those are just the things we have the time and funding to study,” said Smith. “There are probably myriad other effects just waiting to be discovered.”

Next week: The last in our wolves installment will look at “Wolf Island,” excerpts from a book about local gray wolf biology.