 With their complex reproductive needs and permeable skins , amphibians are often considered to be ecological indicators . In many terrestrial ecosystems , they constitute one of the largest parts of the vertebrate biomass . Any decline in amphibian numbers will affect 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 . 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 <unk> ) , 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 . 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 . 
