25 years after returning to Yellowstone, wolves have helped stabilize the ecosystem, Peterson 2020

Compendium Volume 5 Number 2 January 2022

Before the 1900s, wolves and other predators, such as bears and mountain lions, helped control the populations of herbivores in Yellowstone. However, the federal government exterminated these predators in a coordinated campaign. After the last wolf pack was killed, the elk numbers started increasing uncountably. The US Park Service subsequently attempted to control the elk population by shooting the animals or moving them out of the park.

When the park stopped killing elk in 1968, numbers shot up again from about 5,000 to close to 20,000. For the next several decades, elk cycled through population booms and collapses along with climate fluctuations; hard winters left the ground littered with hundreds of the carcasses of elk that had starved to death [Peterson 2020].

Wildlife officials, therefore, reintroduced wolves back to Yellowstone 25 years ago, which brought the elk population under control and ended their extreme population fluctuations due to climate variability. To study how the wolves maintained the balance, the scientists tracked the wolf packs and recorded details of elk kills by the wolves.

They found that the wolves killed cow elk during the years with normal amounts of rain and snow. During the dry years, when there is less vegetation and therefore less elk food, the wolves targeted bulls. The undernourished elk are generally easier to catch, so the wolves target bulls given their larger size. Sparing elk cows allows the elk to reproduce.

The wolves improve elk herd resilience by eliminating the weak and sick animals. Scientists believed the elk herds are now better prepared for climate change impact, such as the frequent droughts.

The result of reintroducing wolves to Yellowstone showed that wolves stabilize the elk population better than humans can. Now wolves may be reintroduced to other states which are home to a large number of elk.

Peterson, Christine, 25 years after returning to Yellowstone, wolves have helped stabilize the ecosystem, National Geographic (July 10, 2020), https://www.nationalgeographic.com/animals/article/yellowstone-wolves-reintroduction-helped-stabilize-ecosystem

For the full PDF version of the compendium issue where this article appears, visit Compendium Volume 5 Number 2 January 2022