Environmental Engineering Reference
In-Depth Information
The last word in ignorance is the person who says of an ani-
mal or plant: “What good is it?” ...If the land mechanism
as a whole is good, then every part of it is good, whether we
understand it or not. ...Harmony with land is like harmony
with a friend; you cannot cherish his right hand and chop off
his left.
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LDO
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EOPOLD
logical roles in the biological communities where it is
found.
In
biological extinction,
a species is no longer found
anywhere on the earth (Figure 9-2 and Case Study,
p. 183). Biological extinction is forever.
Science: Endangered and Threatened Species—
Ecological Smoke Alarms
An endangered species could soon become extinct; a
threatened species is likely to become extinct.
Biologists classify species heading toward biological
extinction as either
endangered
or
threatened
(Figure 9-3,
p. 186). An
endangered species
has so few individual
survivors that the species could soon become extinct
over all or most of its natural range. A
threatened spe-
cies
(also known as a vulnerable species) is still abun-
dant in its natural range but because of declining num-
bers is likely to become endangered in the near future.
Some species have characteristics that make them
especially vulnerable to ecological and biological
extinction (Figure 9-4, p. 188). As biodiversity expert
Edward O. Wilson puts it, “the first animal species to
go are the big, the slow, the tasty, and those with valu-
able parts such as tusks and skins.”
One 2000 study found that human activities
threaten several types of species with premature
extinction (Figure 9-5, p. 188). Another 2000 survey by
the Nature Conservancy and the Association for Biodi-
versity Information found that about one-third of the
21,000 plant and animal species in the United States
are vulnerable to premature extinction.
This chapter looks at the problem of premature extinc-
tion of species by human activities and ways to reduce
this threat to the world's biodiversity. It addresses the
following questions:
How do biologists estimate extinction rates, and
how do human activities affect these rates?
■
Why should we care about protecting wild
species?
■
Which human activities endanger wildlife?
■
How can we help prevent premature extinction of
species?
■
What is reconciliation ecology, and how can it help
prevent premature extinction of species?
■
KEY IDEAS
■
The current rate of extinction is at least 1,000 to
10,000 times the rate before humans arrived on earth,
and it is expected to increase in the future.
■
The greatest threat to a species is the loss and
degradation of the place where it lives, followed by
the accidental or deliberate introduction of harmful
nonnative species.
■
One of the world's most far-reaching and controver-
sial environmental laws is the U.S. Endangered
Species Act, which was passed in 1973.
■
Reconciliation ecology involves finding ways to
share the places that we dominate with other species.
Science: Estimating Extinction Rates
Scientists use measurements and models to estimate
extinction rates.
Biologists estimate that more than 99.9% of all species
that have ever existed are now extinct because of a
combination of background extinctions, mass extinc-
tions, and mass depletions taking place over thousands
to millions of years. Biologists also talk of an
extinction
spasm,
wherein large numbers of species are lost over a
period of a few centuries or at most 1,000 years.
Biologists trying to catalog extinctions have three
problems.
First,
the extinction of a species typically
takes such a long time that it is not easy to document.
Second,
we have identified only 1.4-1.8 million of the
world's estimated 5-100 million species.
Third,
we
know little about most of the species we have identified.
The truth is that we do not know how many
species become extinct each year mostly because of
our activities. Scientists simply do the best they can
with the tools they have to estimate past and projected
future extinction rates.
9-1
SPECIES EXTINCTION
Science: Three Types of Species Extinction
Species can become extinct locally, ecologically, or
globally.
Biologists distinguish among three levels of species ex-
tinction.
Local extinction
occurs when a species is no
longer found in an area it once inhabited but is still
found elsewhere in the world. Most local extinctions
involve losses of one or more populations of species.
Ecological extinction
occurs when so few members
of a species are left that it can no longer play its eco-
