Final answer:
The reintroduction of gray wolves would likely lead to a decrease in the elk population and an increase in the willow population, demonstrating their impact as a keystone species.
Step-by-step explanation:
The reintroduction of the gray wolves into Yellowstone National Park in 1995 is a classic example of how a keystone species can dramatically alter an ecosystem. Wolves, being top predators, prey on elk, leading to a decrease in the elk population.
Consequently, this change in elk behavior to avoid predation resulted in less grazing near streambanks. The reduced grazing pressure allowed willow and other vegetation to regenerate.
which led to a series of ecological improvements, including decreased erosion, improved fish habitat, and the creation of an environment conducive to species such as beavers.
Overall, the willow population would increase as a result of less grazing pressure, while the elk population would decrease due to predation by wolves.