New research on loss of species indicates that extinctions are
occurring now at a rate 100 to 1000 times as fast as "natural
background" rates of extinction. The "natural background" is the
rate of extinction measurable in the fossil record of life before
humans appeared on the scene. In some regions, the rate today is 10,000
times as fast as the natural rate. Extinction is nothing new; it has
been going on since life first emerged on Earth, perhaps 3 billion
years ago. What is new is the speed with which extinctions are now
The most recent estimate of the "background" rate of extinctions
indicates that one species is lost per year out of each 1 million to 10
million species in existence. (No one knows how many species exist.
About 1.4 million species have been named and cataloged; Harvard
biologist E.O. Wilson says his best guess is that somewhere between 5
and 30 million species exist.)
A recent conservative (meaning on the low side; not exaggerated)
estimate of the present rate of species loss suggests that we are
losing one species per year for every 10,000 species on Earth. Thus the
present extinction rate is 100 to 1000 times as fast as the historical
Extinctions are particularly important problems because they are
permanent and cannot be reversed once they occur. When a species is
lost, all of the genetic information that it contained is lost as well.
If a species has valuable characteristics --like the bread mold that
gave us penicillin --its loss is particularly important to humans. But,
in a crucial way, all species are important. We do not know what holds
the web of life together. It is as if we were flying in an airplane and
periodically reaching down, pulling a component out of the control
panel, and tossing it out the window. Anyone can see that such a plane
will very likely not remain airborne. It is the same with biodiversity
--the loss of component parts weakens the whole structure in ways that
we cannot understand or appreciate. We just know that loss of species
cannot be good for the system, or for us.
Why are we losing species so fast? A recent look at the loss of
amphibians (frogs, toads, and salamanders) reveals many complex
There are 5130 species of amphibians on Earth today. Amphibians have
been on the Earth for well over 100 million years --1000 times as long
as HOMO SAPIENS has been around. In other words, humans in their
modern form have been on Earth only one-tenth of one-percent of the
time that amphibians have been here. Amphibians managed to live through
the stressful time when the dinosaurs went extinct, 65 million years
ago. Clearly, amphibians are survivors.
Since about 1970, however, there has been accumulating evidence that
amphibians are declining and disappearing in places as diverse as North
America, Central and South America, Europe, Asia, Africa and Australia.
The rate of amphibian extinctions has been estimated as follows: there
are about 4000 species of frogs and toads; only 5 are thought to have
become extinct between the 19th century and the 1960s. But in the past
25 years, herpetologists have observed drastic population declines and
disappearances of many more species. They believe that 89 amphibian
species are now at risk of extinction. Other species have not been
seen in recent years, but it is not known whether this is due to
natural fluctuations of population or is a sign of trouble.
Why has the rate of amphibian extinctions increased so rapidly this
century and especially within the last 30 years? Specialists writing in
SCIENTIFIC AMERICAN and elsewhere list the following reasons:
1) Amphibians are born of eggs laid in water, eggs not protected by a
leathery or hard shell. Thus amphibians start "sampling" the
environment as soon as life begins.
2) During early life (egg and larval stages), they live in the water;
during later stages, they live partly in water and partly on land. Thus
they "sample" a spectrum of environments as their lives progress.
3) Amphibians have a permeable, exposed skin, not covered by thick
scales, hair or feathers. They breathe (respire) through their thin,
moist skin, again "sampling" the environment and whatever pollutants it
may contain. Because they are "cold blooded" (having no internal
thermostat), they move in and out of sunlight to avoid extremes of heat
4) Habitat loss: The U.S. originally contained between 148 and 185
million acres of wetlands; during the 1950s to 1970s, about 10% of
these wetlands were drained. Currently an estimated 107 million acres,
or between 58% and 72% of the nation's original wetlands, remain in the
continental U.S. Nearly 300,000 acres of wetlands are lost per year.
 Amphibians depend upon wetlands for life. [Solution: protect
5) Habitat fragmentation. Amphibians live in local colonies. When one
colony's habitat is damaged, it might migrate to a new location if
conditions are right. But habitats have been fragmented --cut up by
human developments --so that migration to new habitat is made difficult
or impossible. [Solution: Stop building new roads. Stop clearcutting
forests. Learn to live within reasonable limits. Plan our land uses on
the assumption that other species have a right to exist and that humans
are diminished when other species decline.]
6) Introduction of exotic species for recreational fishing. Exotic
species may outcompete indigenous species for food and breeding sites
or may prey upon the indigenous species. In the U.S., introduced
species such as rainbow trout, golden trout, brook charr, and
largemouth bass eat eggs, larvae and adult amphibians. [Solution:
minimize introduction of exotic species. The stocking of rivers and
lakes with hatchery-bred fish gives the false impression that all is
well, so we could give ourselves a much-needed reality check by
abandoning this practice. Amphibian declines offer a second good reason
to abandon this practice.]
7) Global climate change. Normally, the Earth's ozone shield filters
out the sun's deadly ultraviolet radiation. In the last 30 years,
humans have depleted the ozone shield by chemical contamination, thus
increasing the amount of ultraviolet radiation striking the surface of
the Earth. Field experiments by biologists in Oregon showed that the
eggs of certain species of amphibians are killed by increased exposure
to ultraviolet light. They concluded, "Clearly, amphibian eggs in wild
populations were dying from exposure to ultraviolet-B radiation."
[Solution: aggressively ban all ozone depleters including CFCs, HCFCs
and methyl bromide, and attempt to shut down the black market in such
8) These same scientists note that certain bacteria and fungi have been
known to decimate amphibian populations. One particular fungus is
carried by fish raised in hatcheries; when the fish are released, the
fungus may harm local amphibian populations. These scientists
speculate that, because ultraviolet light is known to harm the immune
system of many animals, ozone depletion may be harming the immune
systems of amphibians, diminishing their defenses against bacteria and
fungi. [Solution: see No. 7, above.]
9) Acid rain, snow, and fog: acidity itself seems to harm growth and
development of amphibians; it also releases aluminum from the soil
which then harms growth and development of amphibians. [Solution:
phase out coal-burning power plants and replace them with solar-
10) Agricultural contaminants: In the western U.S., agriculture uses
80-90% of available water. Recently, 31 of 50 states, plus the Virgin
Islands and Puerto Rico, have reported concerns about groundwater
contamination by pesticides; there are few data on the effects of
pesticides on amphibians. Recent studies at the Klamath Basin National
Wildlife Refuge showed that irrigation drainwater was either lethal to,
or caused significant malformation of, developing frog embryos. The
study concluded that poor water quality (elevated pH [8.0 to 10.4] and
un-ionized ammonia) and/or pesticides may be contributing to the
decline of indigenous frog populations. [Solution: help chemical-
dependent farmers adopt organic farming techniques; this means revising
the institutional framework of agriculture, including loan policies of
private and public lenders, as well as turning much of the Agricultural
Extension Service on its head.]
11) Overharvesting of frogs for human food: The importance of frog legs
as a food item in France has apparently been linked to a marked decline
in native frogs in Europe, India, and Bangladesh. The demand for
frog legs in France is tremendous: the French eat 3,000 to 4,000 metric
tons of them a year. Some 20,000 frogs must be sacrificed in order to
supply a single metric ton of legs.
12) Certain industrial chemicals can mimic the activity of naturally
occurring hormones. Examination of birds, fish and reptiles indicates
that these substances can have drastic consequences, such as a
reduction in sperm count and the alteration of male genitalia.
[Solution: Ban and phase out chlorine as an industrial feedstock. Adopt
the principle of "reverse onus," which says that new chemicals shall be
assumed dangerous until they are shown to be compatible with natural
systems.] (See REHW #378.)
At the most immediate, practical, monetary level, it makes no sense to
ignore the decline and disappearance of species. From the perspective
of humans, amphibians represent a storehouse of pharmaceutical products
waiting to be tapped fully. Hundreds of chemical secretions have been
isolated from amphibian skin, and scientists are just beginning to
learn how valuable these substances may be. Some of these compounds are
already used as painkillers and in treatment of victims of traumas
ranging from burns to heart attacks. It is clearly in our own interests
to stop the destruction of amphibians, and of all other creatures great
 Stuart Pimm, "Seeds of Our Own Destruction," NEW SCIENTIST Vol.
146, No. 1972 (April 8, 1995), pgs. 31-35.
 E.O. Wilson, "The Current State of Biodiversity," in E.O. Wilson
and Frances M. Peter, editors, BIODIVERSITY (Washington, D.C.: National
Academy Press, 1988), pgs. 3-18.
 Andrew R. Blaustein and David B. Wake, "The Puzzle of Declining
Amphibian Populations," SCIENTIFIC AMERICAN Vol. 272, No. 4 (April
1995), pgs. 52-57.
 Andrew R. Blaustein, "Chicken Little or Nero's Fiddle? A
Perspective on Declining Amphibian Populations," HERPETOLOGICA Vol. 50,
No. 1 (March 1994), pgs. 85-97.
 David B. Wake, "Declining Amphibian Populations," SCIENCE Vol. 253
(August 23, 1991), pg. 860.
 Andrew R. Blaustein and David B. Wake, "Declining Amphibian
Populations: A Global Phenomenon," TREE Vol. 5, No. 7 (July 1990), pgs.
 Pimm, cited above, pg. 35.
 Joseph H.K. Pechmann and others, "Declining Amphibian Populations:
The Problem of Separating Human Impacts From Natural Fluctuations,"
SCIENCE Vol. 253 (August 23, 1991), pgs. 892-895.
 Blaustein and Wake, cited above in note 3.
 Robin Boyer and Christian E. Grue, "The Need for Water Quality
Criteria for Frogs," ENVIRONMENTAL HEALTH PERSPECTIVES Vol. 103, No. 4
(April 1995), pgs. 352-357.
 Blaustein and Wake, cited above in note 3, pg. 55, referring to
Andrew R. Blaustein and others, "UV repair and resistance to solar UV-B
in amphibian eggs: A link to population declines?" PROCEEDINGS OF THE
NATIONAL ACADEMY OF SCIENCES Vol. 91 (March 1994), pgs. 1791-1795.
 Andrew R. Blaustein and others, "Pathogenic Fungus Contributes to
Amphibian Losses in the Pacific Northwest," BIOLOGICAL CONSERVATION
Vol. 67 (1994), pgs. 251-254.
 Boyer and Grue, cited above, pg. 353.
 Boyer and Grue, cited above, pg. 354.
 Blaustein and Wake, cited above in note 6, pg. 204.
 Blaustein and Wake, cited above in note 3, pg. 56.
 Blaustein and Wake, cited above in note 3, pg. 56.
 Blaustein and Wake, cited above in note 3, pg. 56.
Descriptor terms: species loss; habitat destruction; habitat
fragmentation; endocrine disrupters; deforestation; clearcutting; frog
legs; france; agriculture; pesticides; fertilizer; acid precipitation;
immune system disorders; bacteria; fungi; fish; exotic species; ozone
depletion; cfcs; hcfcs; methyl bromide; global climate change;
atmosphere; ultraviolet light; hormones; reverse onus; water pollution;
water quality criteria;