 Non @-@ native predators and competitors have also been found to affect the viability of frogs in their habitats . The mountain yellow @-@ legged frog which typically inhabits the Sierra Nevada lakes have seen a decline in numbers due to stocking of non @-@ native fish ( trout ) for recreational fishing . The developing tadpoles and <unk> fall prey to the fish in large numbers . This interference in the frog 's three @-@ year metamorphosis is causing a decline that is manifest throughout their ecosystem . 
