ABSTRACT
The Colorado River drainage contains the largest percentage (74 percent) of endemic fish species of any major drainage in North America (Miller, 1959). This high degree of endemicity is testimony to the long history of isolation of the basin. As a consequence of this isolation, the native fishes form a fundamentally insular fauna. This insular nature is proposed as a major reason underlying the precarious position of major components of the original fish community in the face of habitat alterations and species introductions. This is the thesis I wish to develop in the belief that current theories of insular biogeography and community structure are keys to understanding the history, present status, and future prospects for the native fishes of the Upper Colorado River Basin.
