“How Wolves Change Rivers” is a thought-provoking four-minute mini documentary that went viral with over 44 million views. It showcases the impact of reintroducing wolves to Yellowstone National Park after a 70-year absence, and the resulting trophic cascade, which is an ecological phenomenon caused by the chain of effects on lower trophic levels, shaping ecosystem structure, and nutrient cycling.
The wolves regulated the number of large herbivores in the ecosystem by hunting, and in turn affected the behavior of the prey. As a result, the trees regrew, leading to reforestation, and subsequently stabilized riverbanks. This reintroduction changed not only the biodiversity of Yellowstone but also reshaped the park’s physical geography.
In addition, beavers played a crucial role in this ecological transformation. Their populations recovered thanks to the changes brought on by the reintroduction of wolves, resulting in the availability of woody vegetation which allowed for new habitats for many species.
Beavers are prominent examples of “ecosystem engineers,” modifying their environment with beaver dams and ponds, providing new habitats and influencing many ecosystem processes such as nutrient cycling. Their influence positions beavers as a keystone species, supporting the entire biological community.
The interaction between the keystone species wolf and beaver is complex and is currently being studied by the Voyageurs Wolf Project, which aims to examine the impact of the wolf-beaver dynamic on the ecosystem in and around Voyageurs National Park, Minnesota. The research team is studying how wolf predation affects forest composition by hunting for beavers on logging trails, intimating that wolves influence tree species composition.
Through compelling evidence, it has been established that the presence of wolves impacts the growth and composition of forests due to their effect on the behavior of beavers. Wolves notably influence the habitat engineering role of beavers, creating a visible effect on trees in ecosystems close to ponds, tilting towards conifer-dominated forests.