Abstract
The installation of Glen Canyon Dam has led to many changes in the Colorado River corridor through the Grand Canyon. The effect of the dam on mammals, amphibians, and reptiles is not well understood and poorly studied, but in general is considered positive. A number of animal species, specifically those associated with riparian habitat, have increased in numbers since the dam was closed. Toads, lizards, beaver, small mammals, scavengers, and bighorn sheep are among those species that have probably benefited from the dam’s flow regulation. Increases in riparian vegetation, available riparian habitat, insect abundances, and outside food from humans have all contributed to these population changes. The current and future Adaptive Management practices of fluctuating flows and controlled floods aim to decrease riparian vegetation, and may therefore lead to a decrease in habitat and food availability. This could in turn cause a decline in many animal species. However, these declines will probably be small, and are not likely to threaten mammal, amphibian, or reptile populations. Monitoring of these species is essential to ensure that changes in dam operations do not adversely affect their populations.