This study examines the ecological impacts of reintroducing apex predators in Yellowstone National Park’s northern range, specifically gray wolves, cougars and grizzly bears. Historically, predator removal led to elk overpopulation and a shift from a beaver-willow to an elk-grassland ecosystem. The study hypothesizes that restoring predators will reverse these changes, but an alternative hypothesis suggests the ecosystem is in a resistant stable state. A 20-year study, involving simulated beaver dams and browsing exclusion, monitored willow growth, herbivore populations and hydrology. Key findings showed willow growth only occurred with reduced browsing and simulated beaver dams, and the elk-grassland state persisted. Bison populations increased and remained unaffected by predators. This indicates ecosystem restoration requires an integrated approach, considering factors beyond predators, such as hydrology and herbivore behavior, and acknowledges potential alternative stable states. Simply reintroducing predators may not be sufficient for ecosystem recovery.
