This is because during the process of metamorphorsis many die and others are destroyed by predators. Metamorohosis alters the feeding and breathing habits of an animal as well as its physical shape. Amphibians change from gill breathers to lung breathers. They also change from plant eaters to meat eaters. Adults eat insects or small animals.
Some frogs eat small mammals and birds.
Most amphibians reach maturity at three or four years. They breed fot the first time about one year after metamorphosis. Although some amphibians carry their eggs withing their bodies until hatching takes place, most lay eggs in moist places to allow their offspring to develop at least to the larval stage before hatching. Some species abandon their eggs in a pool, a stream, or some other moist place, but others watch over their eggs until they hatch. The life span of an amphiban depends on its species and on its environment.