Nature is a fickle beast. If one thing changes, it can effect the entire ecosystem. In fact, there is no place where the butterfly effect is more apparent than in nature.
Take Yellowstone National Park, for example. This massive nature preserve had not been home to wolves for almost 70 years, but when they were reintroduced, the entire landscape of the park radically changed.
It's amazing how one pack of wolves could cause such a drastic change, but that's just the way nature works. This is exactly why we need to take more stock in how our actions affect the environment. One small change is enough to disturb the balance of entire ecosystems.