Amphibians are a class of cold-blooded vertebrates that includes frogs, toads, salamanders and caecilians. They are distinct in usually having dual life stages, most species beginning life in water and then transforming into air-breathing adults that rely heavily on permeable skin.
Unlike reptiles, they lack protective scales and must remain closely tied to moist environments. Moreover, unlike fish, birds and mammals, they are almost entirely absent from marine environments because saltwater is toxic to their permeable skin.
Scientists currently recognize more than 9,000 amphibian species distributed across three major orders and several dozen families and hundreds of genera. Frogs and toads make up the majority of this diversity, followed by salamanders and the lesser-known limbless caecilians. They occupy a wide range of ecosystems including tropical forests, temperate wetlands, mountain streams and even some arid regions where they survive through burrowing and seasonal activity.
Despite their relatively small size and often hidden lifestyles, amphibians play disproportionately large roles in ecosystem function. Their environmental importance is closely tied to their position in food webs and their sensitivity to change. They serve as both predators and prey, consuming insects and other invertebrates while supporting birds, fish and mammals. By regulating insect populations, they help maintain ecological balance and reduce the spread of pests and disease vectors.
Their permeable skin allows for the exchange of water and gases directly with the environment, which also makes them highly responsive to pollution and climate shifts. As a result, amphibians are widely regarded as biological indicators, with population declines often signaling deeper environmental problems such as water contamination or habitat degradation.
Amphibians also contribute to agriculture, although their role is less visible than that of birds. Many species consume large numbers of crop-damaging insects, particularly in rice paddies and other wet agricultural systems, offering natural pest control that can reduce dependence on chemical pesticides.
Their presence can support more balanced and sustainable farming practices, particularly in regions where integrated pest management is used. Additionally, amphibians contribute to nutrient cycling by moving energy between aquatic and terrestrial systems during their life cycles.
Despite their ecological value, amphibians are among the most threatened groups of vertebrates. Current estimates indicate that around 40 percent of amphibian species are threatened with extinction, a proportion significantly higher than that of birds or mammals.
This is largely the result of habitat loss caused by wetlands draining, forest clearing and alteration of freshwater systems. It is also due to climate change, which disrupts breeding cycles and reduces the availability of suitable habitats, especially for species with narrow environmental tolerances. Additionally, pollution from pesticides and industrial chemicals can be absorbed directly through amphibian skin, leading to deformities or death. Still another major cause of amphibian declines is the global wildlife trade (i.e., the legal and illegal pet trade).
Disease has emerged as an especially severe threat. The spread of the deadly chytrid fungus has caused dramatic declines and extinctions in amphibian populations worldwide by disrupting their ability to regulate water and electrolytes. Invasive species also contribute to losses by preying on native amphibians or competing for resources. Because many amphibians have limited ranges and specialized habitat requirements, even small environmental changes can have outsized effects on their survival.
The decline of amphibians carries serious ecological consequences. As their numbers fall, insect populations may rise, affecting both natural ecosystems and agriculture. The loss of amphibians can also disrupt nutrient flows between water and land, weakening ecosystem resilience. These changes can cascade through food webs and reduce biodiversity more broadly.