Human pressures are taking a toll of amphibians
The planet's amphibians are under threat.
Declining populations of frogs, salamanders
and toads have been reported from all over
the globe and some of the amphibian groups
are disappearing completely from their natural habitats.
Frogs are in close communion with their
surroundings - both water and soil - at different times in their life history. Besides, they have different food habits - adult frags are
carnivores, while tadpoles are herbivores.
This makes them suitable indicators of the
state of the planet's health. Scientists argue
that what happens to the f rags is a reflection
of what can happen to humans, as they occupy the same living area (Scientific American, Vol 274, No 4).
Several causes have been suggested for
the decline in amphibian populations - first
recognised as a global phenomenon in 1990.
Andrew Blaustein, professor of ecology at
the Oregon State University says that the
depletion of stratospheric ozone may well be
harming the amphibian species in some parts
of the world. The ozone layer shields the
earth from the Sun's harmful rays. The
ultraviolet rays, particularly ultraviolet-B
(UV-B) radiation - a specific wave-length
of light with a range of 280 to 320
nanometers - is harmful to both plant
and animal life.
Ultraviolet radiation also affects the
aquatic insects population - the food of
the amphibians, and so influences the
amphibian population. Amphibian eggs,
which are normally laid in open, shallow
waters, are not only being exposed to
UV-B radiation but are also being attacked by a fungus - Saprolegnia - which
infects fish like salmon and trout.
Pollution is another factor that affects
the population of amphibians. Frogs are
particularly sensitive to acid rain, insetticides, herbicides and industrial chemicals,
which adversely affect the reproduction and development of
amphibians. Frog populations have
also suffered because of the popularity of frog legs, particularly in France.
One of the biggest human follies has been the introduction of
imported species into an ecosystem.
The introduction of salmon and
trout into streams in California has
resulted in the disappearance of the
mountain yellow-legged frog.
David Wake, professor of biology at the University of California.
Berkeley says that no single explanation fits everycase of declining
amphibian populations, but all
seem to be important to one degree
or another.
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