With their complex reproductive needs and permeable skins, amphibians are often considered to be ecological indicators.[138] In many terrestrial ecosystems, they constitute one of the largest parts of the vertebrate biomass. Any decline in amphibian numbers will have an impact on the patterns of predation. The loss of carnivorous species near the top of the food chain will upset the delicate ecosystem balance and may cause dramatic increases in opportunistic species. In the Middle East, a growing appetite for eating frog legs and the consequent gathering of them for food was linked to an increase in mosquitoes.[139] Predators that feed on amphibians are affected by their decline. The western terrestrial garter snake (Thamnophis elegans) in California is largely aquatic and depends heavily on two species of frog that are diminishing in numbers, the Yosemite toad (Bufo canorus) and the mountain yellow-legged frog (Rana muscosa), putting the snake's future at risk. If the snake were to become scarce, this would affect birds of prey and other predators that feed on it.[140] Meanwhile, in the ponds and lakes, fewer frogs means fewer tadpoles. These normally play an important role in controlling the growth of algae and also forage on detritus that accumulates as sediment on the bottom. A reduction in the number of tadpoles may lead to an overgrowth of algae, resulting in depletion of oxygen in the water when the algae later die and decompose. Aquatic invertebrates and fish might then die and there would be unpredictable ecological consequences
http://en.wikipedia.org/wiki/Amphibian
http://en.wikipedia.org/wiki/Amphibian