National Park Service policy contains a potential internal tension because it directs park managers both to protect native species and to protect ecological processes. But even without human influences, native species come and go from a landscape. In some cases, were such a situation to develop, other laws would override policy. If ecological processes threaten grizzly bears, for example, the Endangered Species Act would presumably require the National Park Service to find ways to protect and sustain the grizzly bear population. But in most cases, which would involve species that are probably abundant elsewhere and need no special local protection, it is more likely that the species would not receive special protection.
Biodiversity has several levels of meaning in a landscape.
At another level, it may involve the diversity of species that inhabit a landscape, and is often referred to Alpha diversity. As explained earlier, in the history of the northern range issue, the first concerns over species diversity involved the herbivores that some people believed were being pushed out by the elk. More important, elk are not threatening the more common northern range ungulates. No significant relationship has been found between elk and pronghorn numbers, and bison and mule deer numbers have increased along with elk numbers during the past three decades. Numerous investigators, cited earlier, have demonstrated that grazing and browsing of northern range plant species by ungulates does not decrease native plant species diversity.