B.C. Frogwatch Program
What are these Amphibians anyway?
(and why are we watching them?)
Amphibians are a class of vertebrate animals that have a characteristic two-stage life cycle. The name
amphibian comes from the Greek amphi- (two) and bios (life). Living amphibians include anurans
(frogs and toads), salamanders, and caecilians; there are about 4000 species in the world, mainly anurans.
The fossil record shows that some of the first vertebrate land animals were amphibians;
they were not the same species as today's amphibians, but they lived in the same way.
Some were very large - imagine a six-foot salamander!
Frogs, toads, and some salamanders go through an aquatic (water dwelling) "larval" stage
with gills, and then metamorphose (transform) into an adult form that lives on land and
breathes air. You have probably seen the transformation of tadpoles into frogs. Because
they live in two habitats, amphibians are uniquely sensitive to environmental changes. They
get a double whammy, so to speak, of pollutants or other environmental problems.
Most amphibians have smooth, moist skin that is very permeable to substances in the
water or the atmosphere. Adult frogs absorb part of the oxygen and most of the water
they need through their skin, and some salamanders get all their oxygen this way since
they have no lungs at all! While this permeable quality of the skin helps the amphibians
in some ways, it also makes them vulnerable to pollutants.
Scientists began to notice a decline in the numbers of amphibians, especially frogs,
about ten years ago. Since then it's become obvious that something is very wrong -
entire populations and even species of frogs seem to be disappearing, even from
apparently pristine areas. Scientists now think that the frogs' declines are not
caused by any single factor but by a complex of causes, including habitat loss,
pollution, ozone layer depletion (increased UV), and disease. It is distressing to see
how many of these factors have to do with human activities. Even the diseases may have
been spread by the introduction of exotic species to different ecosystems by
people. It is important for us to learn more about these declines and to do our best
to try to reverse them.
Photo © Russ Haycock. No reproduction or distribution without permission.
