The return of a single species to Yellowstone has revitalized the entire ecosystem. Which species are we talking about?

The concept that the return or disappearance of top predators can impact every part of the food chain and the ecosystem as a whole seems to have been validated. In a new study, researchers summarized a 20-year investigation that began in Yellowstone National Park in the 1990s, as reported by Live Science.

In the 1920s, scientists noted that gray wolves (Canis lupus) had completely vanished from Yellowstone National Park, while the population of cougars (Puma concolor) had dwindled to such low numbers that researchers had to monitor them. Consequently, elk (Cervus canadensis) thrived in the absence of these predators, which in turn led to the destruction of certain plant populations. The loss of some trees and shrubs subsequently threatened beaver populations. This sequence of events is known as a trophic cascade — when the actions of top predators indirectly affect other species lower in the food chain, ultimately impacting the entire ecosystem.

It is known that similar trophic cascades have shaped the ecosystems of other parks, such as Olympic National Park in Washington after the wolves disappeared. In the 1980s, researchers observed that the cougar population in Yellowstone had rebounded, and wolves were reintroduced to the park only in 1995 and 1996.

Scientists were uncertain whether the return of predators would restore balance to the park's ecosystem. However, now, in a new study, researchers finally summarize the findings of the 20-year experiment: it is suggested that the return of wolves to the park likely had a cascading effect that benefited the system as a whole.

A team from Oregon State University analyzed data collected from 2001 to 2020 regarding willow shrubs along streams in Yellowstone. The researchers examined the crown volume of willows — the total space occupied by the branches, stems, and leaves of the shrub — and this measurement allowed them to calculate the total biomass of the shrubs.

According to the study's lead author, William Ripple, the analysis results indicated a 1500% increase in willow crown volume along the streams during the study period, which signifies a significant recovery of these shrubs. The study links this substantial recovery of willow shrubs to a decrease in browsing by moose, likely due to the return of predators to the region.

The new study also emphasizes the importance of long-term monitoring, as such changes do not occur overnight, and understanding them requires patience and persistence.

Ripple also notes that he and his colleagues intend to explore other factors in the future, such as how climate change and the growing bison population affect the trophic cascade. Additionally, researchers plan to investigate how beaver populations shape the landscape and ecosystem.