=======================Electronic Edition========================
RACHEL’S ENVIRONMENT & HEALTH WEEKLY #441
—May 11, 1995—
News and resources for environmental justice.
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Environmental Research Foundation
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NEW PERSPECTIVES ON LOSS OF SPECIES
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. [1] 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 occurring.
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.) [2]
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 “background” rate.
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
reasons. [3]
There are 5130 species of amphibians on Earth today. [4]
Amphibians have been on the Earth for well over 100 million years
–1000 times as long as HOMO SAPIENS has been around. [5] 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. [6]
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. [7] 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. [8]
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: [9]
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 and cold.
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. [10] Amphibians depend upon wetlands
for life. [Solution: protect wetlands.]
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.” [11][Solution: aggressively ban all ozone depleters
including CFCs, HCFCs and methyl bromide, and attempt to shut
down the black market in such products.]
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. [12] 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. [13]
[Solution: phase out coal-burning power plants and replace them
with solar-hydrogen systems.]
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. [14] [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. [15] 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. [16]
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. [17][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 RHWN #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 and small. [18]
                
                
                
                
    
–Peter Montague
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[1] Stuart Pimm, “Seeds of Our Own destruction,” NEW SCIENTIST
Vol. 146, No. 1972 (April 8, 1995), pgs. 31-35.
[5] David B. Wake, “Declining Amphibian Populations,” SCIENCE
Vol. 253 (August 23, 1991), pg. 860.
[7] Pimm, cited above, pg. 35.
[9] Blaustein and Wake, cited above in note 3.
[13] Boyer and Grue, cited above, pg. 353.
[14] Boyer and Grue, cited above, pg. 354.
[15] Blaustein and Wake, cited above in note 6, pg. 204.
[16] Blaustein and Wake, cited above in note 3, pg. 56.
[17] Blaustein and Wake, cited above in note 3, pg. 56.
[18] 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; fertilizers; 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;