Many of our endangered plants and animals are found in only a few, or sometimes even a single small area. This makes the risk factor for extinction very high should something negatively impact that habitat, such as fire, deforestation, or introduced predators. Extinction is a natural process. Today, extinction rates are many times greater than the natural rate. If we are to save what is left, today's unnatural rates of extinction cannot continue.
Extinction is irreversible.
There is no way to replace a species once all of its members are gone. As in the example of the nene, a species can be brought back from the brink of extinction, but it requires human intervention.