One of the most important things to remember about ecosystems and environments is that every species living within the environment plays a role that affects all other species in that environment. One direct way is through the predator/prey system. If a lion's main food source is the zebra and the zebra becomes extinct, then the lion's food resource is removed, greatly affecting its survival. It works the other way around as well. If a shark eats fish, but the shark goes extinct, that fish population will get very large and may have negative affects on the environment. One result may be that the environment cannot supply enough food for the increased population, so those fish either die or adjust their diet. The effect of extinction not only influences other animals, but it also greatly impacts plants and other living species. Plants rely on animals for a lot of things and vice versa (oxygen, carbon dioxide, nutrients, food, water, balance of environmental chemicals).So in short the extinction of a species has a chain reaction effect, impacting the survival and living conditions of many other species, both plant and animal.