When a top predator is removed from an ecosystem, its prey species can multiply unchecked. This often leads to overgrazing or over-browsing of vegetation, which in turn affects plant communities and the animals that depend on those plants for food and shelter. Conversely, the introduction or reintroduction of a top predator can help control the population of herbivores, allowing vegetation to recover and thrive. This recovery can benefit a wide array of other species, illustrating the interconnected nature of ecosystems.
Perhaps the most famous example of a trophic cascade is the reintroduction of wolves to Yellowstone National Park in the United States. Before wolves were reintroduced in the mid-1990s, elk populations (American elk, not to be confused with European elk, known as Moose in the Americas) had grown excessively, leading to overgrazing and a decline in the health of plant communities. When wolves were brought back, they began preying on the elk, reducing their numbers and altering their grazing behaviour. This allowed overgrazed areas to recover, leading to increased growth of trees and shrubs. These changes provided better habitats for species such as beavers and songbirds, showcasing the cascading effects of predator-prey interactions.
