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Wolves Keep Yellowstone in Balance

In the 1920s, government policy allowed the extermination of Yellowstone's gray wolf -- the apex predator -- triggering an ecosystem collapse known as trophic cascade.

In the 1920s, government policy allowed the extermination of Yellowstone’s gray wolf — the apex predator — triggering an ecosystem collapse known as trophic cascade.

In 1995 — through use of the Endangered Species Act — the conservation community reintroduced the gray wolf to restore balance. The impact is dramatic.

Elk populations exploded without wolves as their primary predator, resulting in severe overgrazing of willows and aspen. These trees are critical to beavers for food, shelter and dam building.

Elk populations exploded without wolves as their primary predator, resulting in severe overgrazing of willows and aspen. These trees are critical to beavers for food, shelter, and dam building.

Scavenger species such as bears, ravens and eagles suffered without year-round wolf kills to feed on. After wolves were reintroduced in 1995 in Yellowstone's northern range, scavengers have reaped the benefits of regular, wolf-supplied meals.

Various scavenger species suffered without year-round wolf kills to feed on.

Beavers virtually disappeared in the northern range of Yellowstone. Their dams disintegrated, turning marshy ponds into streams. Heavy stream erosion occurred. Many plant and animal species were affected.

Beavers virtually disappeared in the northern range of Yellowstone. Dams disintegrated, turning marshy ponds into streams. Massive loss of mature willows and aspens. Heavy stream erosion. Many plant and animal species were affected.

Coyotes became an apex predator without wolves, driving down populations of pronghorn antelope, red fox and rodents, and birds that prey on small animals.

Without wolves, the coyote became an apex predator, driving down populations of pronghorn antelope, red fox, and rodents, and birds that prey on small animals.

In 1995, wolves were reintroduced to the northern range of Yellowstone. Coyote numbers have dropped by half, allowing antelope, rodent and fox populations to increase.

As the wolf returns, coyote numbers drop by half, allowing antelope, rodent, and fox populations to increase.

After wolf reintroduction in the northern range, elk numbers drop and beaver colonies increase from 1 to 12. Insects, songbirds, fish, and amphibians thrive.

Today, biodiversity is enriched and scavenger species reap the benefits of regular, wolf-supplied meals.

All imperiled wildlife could soon be under fire due to a series of regulatory rollbacks to the Endangered Species Act. The Trump administration is seeking to remove protections for wolves across the entire contiguous United States. Urge your governor to stand up for the Endangered Species Act and for wolf recovery by opposing the national wolf-delisting plan.