Scientists believe that the earliest relatives of modern amphibians, the first land vertebrates, emerged from the water approximately 400 million years ago. In the 100 million years that followed (before the rise of the reptiles) amphibians achieved a great degree of diversity. Today, there are only 4,800 species of amphibians worldwide, divided into three orders, Anura (frogs and toads), Apoda (caecilians), and Caudata (salamanders and newts). There are 193 species of amphibians which can be found in North America, of which two species of anurans representing two families have been documented within the Preserve.
Amphibians evolved from life in the water and are still closely tied to water today. Amphibians have a thin skin that is not covered by hair, feathers, or scales (except in a very few cases). This thinness allows them to both breathe and drink through their entire surface of their bodies. It also makes them highly susceptible to desiccation (drying out), one reason why not many amphibians are found in the desert. (There are also no marine amphibians – they would loose water from their bodies through their permeable skins to the salty ocean water.) The amphibians that are found in the Preserve live in riparian areas such as springs or seeps where they have access to water. Most amphibians also require water to lay their eggs in. The larval form of frogs and toads is called a tadpole, a free-swimming organism that breathes with gills and looks radically different from the adult form. Adult frogs and toads also do not possess a tail. Anurans are the most vocal of all amphibians.
The red-spotted toad (Bufo punctatus) is a member of Bufonidae, the true toad family. Although there is no scientific distinction, toads tend to have warty skin which is drier than that of frogs, relatively shorter hind limbs for hopping and walking, and spend more time on dry land. The parotid glands (behind the eyes) and warts of true toads can secrete a sticky white poison that can be deadly to some predators. There is no danger in handling these toads however, and touching them does not cause warts. The red-spotted toad is a good climber and may be found on or among rocks.
The pacific treefrog (Pseudacris regilla) is a member of Hylidae, the treefrog family. Frogs generally have smoother skin than toads, longer hind limbs for leaping and climbing, and spend more time in the water. Contrary to its name, the pacific treefrog is a ground-dweller and is usually found near water among low vegetation. Both pacific treefrogs and red-spotted toads have been observed at Cornfield Spring, one of the few perennial sources of water in the Preserve, in recent years.
Amphibians species all over the world are in decline and have been for many years. Some of these cases can be attributed directly to localized events, such as habitat loss due to logging or draining of wetlands. However, scientists are discovering that amphibian populations in protected, seemingly pristine areas like national parks and refuges are also in decline. Because of their thin skin and ability to take up substances through it, they are often more susceptible to pollutants than are other types of animals and are considered by many to be important environmental indicators. Although the cause of the decline in many amphibian species is unknown, some scientists believe that global changes such as increased ultraviolet radiation caused by the depletion of the ozone layer or the accumulation of pollutants in the environment may be at fault.
