How many wolves were reintroduced to Yellowstone to restore the original ecosystem through a trophic cascade?

• A. 20 wolves
• B. 60 wolves
• C. 100 wolves
• D. 41 wolves

Answer: (D)

Restoring an apex predator can trigger a trophic cascade that rebalances an ecosystem. In Yellowstone, 41 wolves were released in the mid-1990s from Canada to establish a viable, genetically diverse population across the park. This number was enough to form multiple packs and spread through key areas, creating widespread predation pressure on elk. As wolves began to influence where and how elk graze, elk browsing declined in riparian and other sensitive zones. That relief allowed vegetation like willows and aspens to recover, which in turn supported better habitat for beavers, songbirds, and other wildlife, and even affected stream structure and fish habitat. The 41-wolf release was sufficient to kick a self-sustaining ecological response, whereas too small a release might not have established stable wolf populations or produced broad ecosystem changes.