This will shatter your view of apex predators.
70 years ago, northwestern wolves were hunted to extinction in Yellowstone National Park, Wyoming. They were mistakenly considered a huge danger to the safety of human visitors to the park, so were eliminated by rangers. However, unbeknownst to the owners at the time, the extinction of the wolves had a massive effect on the whole ecosystem of the park. Removing a key predator had a huge knock on effect on the food chain, drastically altering the levels of flora and fauna in Yellowstone.
So when, in 1995, the wolves were reintroduced to the park, the ecosystem began to correct itself back to the levels of the 1930s. The wolves’ return led to what is called a trophic cascade – the phenomenon where the presence of a predator alters the number and behavior of their prey, which in turn has a knock on effect on the food chain. Vegetation has improved and wildlife has increased in number. In particular, the wolves caused an incredibly positive and extremely dramatic effect on the rivers.