What are Amphibians?

Amphibians form a class of vertebrates. Other classes include reptiles, birds and mammals. There are over 4700 species of amphibians worldwide, making this group more diverse than mammals. Amphibians have no unique structure, like the feathers of birds, which sets them apart from all other animals, but there are a few characteristics which all amphibians share:

• They are ectotherms (often referred to as cold-blooded). This means that amphibians do not hold their body temperature constant like mammals, but their internal temperature depends upon that of the surrounding environment.
• Amphibians have soft, generally moist skin without scales.
• Their eggs do not have shells and so must be laid in water or a damp environment to keep from drying out.
• Amphibians go through a two-stage life cycle. When an amphibian hatches it is in a gilled larval form. In frogs and toads this larva is called a tadpole. After a few weeks or months the larvae transform into the adult form, however it may still take a few years to become mature.

Biologists divide amphibians into three orders. Two of these, the frogs (including toads) and the salamanders are found in Canada. The third group is the caecilians -- limbless amphibians found only in the tropics. Frogs are by far the most diverse group of amphibians, with over 4000 species worldwide.

Amphibians in Prince Edward Island

Frogs, toads, salamanders and newts are all amphibians. These animals rely on outside temperatures to keep their bodies warm enough to survive. This is not always easy in Prince Edward Island! The work amphibian means "double-life", in reference to living both in water and on land. Most amphibians lay their eggs, protected only by jelly, in the water. The young go through a larval stage, breathing through gills and swimming with fins, before transforming into adults. Although most species have lungs, they also breathe through their moist skin and the lining of their mouths. Amphibians do not drink water; instead they absorb it through their mucous-moistened skin.

Amphibians are a part of local biodiversity: the amazing variety of life around us. Conserving biodiversity is essential to the health of the planet and the welfare of humankind. Amphibians also have a special role to play in keeping the environment healthy. Perhaps because they live "on the edge" between water and land, amphibians are very sensitive to pollution and other environmental changes. Worldwide, many species are declining in numbers or have recently become extinct. By tracking the health of amphibian populations, we can detect larger environmental problems.

The amphibians of Prince Edward Island hibernate in winter. With the warmth of spring they emerge and migrate to traditional breeding ponds. The males of most species call to attract mates in a lively chorus, while voiceless salamanders search for their mates by smell. Mating and egg laying take place in the water, where eggs and young are left to fend for themselves.

The eggs develop rapidly and hatch into larvae. Frog and toad larvae, called tadpoles, are good swimmers and eat mostly plants. Salamander larvae, which eat insects, develop legs quickly so that they can walk on the bottom of the pond. The tadpoles of some species forage in schools and use chemicals to communicate and warn of danger when wounded. Over several weeks the larvae transform into air-breathing, land-dwelling animals. Adult frogs, toads and newts are active in the daylight hours in the Prince Edward Island and feed on insects and other small creatures. Salamanders are nocturnal, hiding under logs and leaf litter. With the onset of freezing temperatures in autumn, amphibians retreat to their hibernating sites.

In winter, amphibians survive by hibernating underground, in pond mud, or under leaf litter beneath a thick blanket of insulating snow. While most amphibians freeze to death if cooled below -1º C or -2º C for more than a brief period, a few northern species actually have antifreeze in their cells to allow them to survive to a temperature of -5º C to -7º C. Wood Frogs, for example, use glucose in their cells as antifreeze that prevents the cells from bursting in these freezing temperatures. In effect, these frogs can be 'frozen solid' during hibernation and still emerge safe and sound in spring.

Amphibians take full advantage of the warmth of the spring and summer sun. Eggs are large and dark to help absorb heat. They are submerged in warmer shallow water, safely below the surface, which might freeze. Tadpoles love to bask in the sun in the shallow while adult frogs and toads bask on land or in shallow water in the heat of the day. Some amphibians, which are nocturnal in warmer climates, prefer the warmest and brightest part of the day in the North.

For more information about Amphibians in Canada, visit the Canadian Amphibian and Reptile Conservation Network website.