I'm writing a story for a character who is a an old monster hunter. In his younger days, he used to make a living by hunting the most dangerous monsters which are basically the story's equivalent of apex predators like tigers or lions. At one time he was tasked to clear a small island of tiger-like monsters, which he did, and he was paid well for that.
Later in his life, he returned to that island, only to find that it's been deserted by the people who lived there because of various ecological disasters. With lack of predators, its prey animals bred out of control, which decimated the vegetation to the point where even trees are eaten by the wildlife until there's none left, which ruins the soil and therefore agriculture (not to mention a period where the inhabitants on the island spend more time fighting off herbivores eating their crops than actually farming). This caused him to realize the error of his ways and he decided to be more conservative in his work, only hunting when it's absolutely necessary and even protecting monsters that are important to the ecosystem.
My question is, is this sort of ecological disaster even possible in a person's lifetime (ideally maybe 20-30 years)? The world of the story is inspired by Monster Hunter where fire or thunder breathing dinosaurs are quite normal and part of the ecosystem, so the science may be able to stretch a little bit.