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Pictured here is a Hylid frog (commonly called a tree frog) from Costa Rica. In the 1980s, reports began to accumulate about the decline of frogs and toads in pristine environments such as nature reserves and parks. This greatly concerned ecologists who look at amphibians as an indicator species, a warning of environmental stress.
The metamorphic life cycle of amphibians -- often egg to tadpole (or other water-living larva) to land-based adult -- relies upon both aquatic and terrestrial habitats. Therefore, because they lack such exterior protection as scales, feathers and hair, they are very sensitive to changes that may occur in their external environment.Image credit: Joseph Kiesecker, Pennsylvania State University
