This means toads act like a barometer for habitat or ecosystem conditions. Southern California does not have a lot of amphibians, and those that are there have adapted to very specific habitats. The arroyo toad, for example, has adapted to life near waterways that often dry up for part of the year, so the species survives best in areas that flood repeatedly. Frequent fires also play a role in maintaining vegetation. When humans develop or alter watersheds, drainages, and streamside areas in southern California, the toad s environment changes to the detriment of the species.
Species exhibit a range of sensitivity to habitat loss and other stresses.
The California red-legged frog, for example, is extremely sensitive to habitat changes. Today, it is gone from 75 percent of its total range and all but one site in southern California. Also in southern California, the mountain yellow-legged frog population has declined to fewer than 100 individuals. Arroyo toads represent a mid-range of sensitivity, so the fact that they have been extirpated from 75 percent of their former range indicates extremely negative changes in the water systems that support the species. Today, the arroyo toad inhabits about 22 watersheds or drainages, and many of the remaining populations are quite small.