Mountains

Sometimes mountains can become refuges for species endangered by the drying climate, or other radical ecological change, in the surrounding lowlands. In this way mountains can influence a species' chances to live and prosper. Climatic "islands" like this may isolate one population from the rest of its species. Entire uncatalogued species of large animals have been found in the 1990s living in the mountains of southeast Asia. As generation succeeds generation, the genetic pattern that defines a population can change during its separation from the rest of its species. An isolated population may even become a species unto itself, unable to reproduce with the population from which it was once separated. This evolutionary phenomenon is called speciation, and mountain topography provides barriers between populations that have made speciation happen.

When the Grand Canyon was cut, speciation occurred in the squirrels that inhabit the high-altitude ponderosa pine forest of the southwest Colorado Plateau. The canyon's steep cliffs and desert terrain contained nothing for a squirrel to eat, so individual squirrels did not enter it. The squirrels stayed at home on the south rim or the north rim, and the populations ceased to interbreed with each other. The eventual result has been speciation: the north rim's Kaibab squirrel and the south rim's Abert squirrel have become separate species.