Loss of biodiversity
Biological diversity must be viewed as a global
resource, like the atmosphere or the oceans. New uses for it are
being discovered that can relieve both human suffering and
environmental destruction. Only a tiny fraction of species with
potential economic importance have been utilized; 20 species supply
90 per cent of the world's food, and just three (wheat, maize, and
rice) provide more than half. In most parts of the world, these few
crops are grown in monocultures that are particularly sensitive to
insect attacks and disease. Yet tens of thousands of edible
species—many possibly superior to those already in
use—remain unexploited. The rapid development of
biotechnology will speed up the use of available genetic resources,
thereby increasing the value of maintaining the most diverse
possible pool of species and genes.
Rapid destruction of the natural environment is
quickly reducing both the number of species and the amount of
genetic variation within individual species. Perhaps a quarter of
the earth's total biological diversity, amounting to about a
million species, is in serious risk of extinction during the next
20 to 30 years. This is perhaps 1,000 times faster than the
historical rate of extinction. If a forest is reduced to 10 per
cent of its original size, the estimated number of species that can
continue to exist in it will decline eventually by half. Habitat
reduction on this scale has already occurred in many parts of the
tropics in recent decades. More than half of the world's species
are believed to live in tropical rain forests. They were
disappearing at a rate of more than 7 million hectares per year in
the early 1980s; this implies a 40 per cent reduction in their
total area from the mid-1980s to 2000. Other species-rich habitats
in danger include tropical coral reefs, geologically ancient lakes,
and coastal wetlands.
Macaws, frogs and toads
In the year 2000, Spix's macaws vanished from
northeast Brazil. The large, powder-blue birds' disappearance was
no fluke. Farmers and timber cutters cleared their wooded river
forest habitat. Bird traders bagged the birds, and hunters shot
them. Today, only 40-60 Spix's macaws still live in aviaries, where
most of them were born. None remain in riverside woodlands where
the birds were "discovered" just 183 years ago.
While scientists puzzle over the prospects for
breeding these birds and releasing their progeny back to the wild,
many wonder how re- introduced birds would learn to locate food.
With little habitat left, they would need to fly to other scattered
habitat "islands" to find enough fruit and seeds to survive. Even
if all of this worked out, the birds' young would be threatened by
an invasive introduced insect—the "Africanized" hybrid
honeybee—that inhabits 40 percent of remaining tree cavities
suitable for macaw nesting.
The demise of the Spix's macaw resonates far
beyond one tiny Brazilian region, for this is far from an isolated
incident. According to a 2000 study published by the global
conservation organization BirdLife International, the Spix's macaw
and almost 1,200 additional species—about 12 percent of the
world's remaining bird species—may face extinction within the
next century. Most struggle against a deadly mixture of threats.
Although some bird extinctions now seem imminent, many can still be
avoided with a deep commitment to bird conservation as an integral
part of a sustainable development strategy.
By the end of the 1980s, at least 14 Australian
amphibian species had gone into serious decline or disappeared
entirely from the eastern mountainous regions of the continent. The
southern dayfrog and the gastric breeding frog, which was only
discovered in 1973, commonly been found in the same areas
have not been seen in the wild since 1981. Three other species in
southeastern Queensland have declined by more than 90 percent.
Further north, in the tropical forests two species declined sharply
in 1985; one of them has not been seen since. And in the tropical
rain forests of northern Queensland, large- scale declines began in
1989—seven species dipped sharply; four can no longer be
found in the wild. All these species were locally endemic: they did
not exist anywhere else in the world.
Several -hypotheses about Australian amphibian
declines have been proposed, but there are no widely accepted,
definitive answers. And the mystery spreads beyond Australia. By
the end of the 1980s, reports of declines and disappearances
emerged from most other regions of the world where amphibians were
reasonably well monitored—in North America, parts of South
America, and Europe. In Costa Rica's Monteverde National Park,
populations of 20 of the 50 native amphibian species, including the
famous Golden Toad, have declined or disappeared since 1987.
And in California's Sierra Nevada, five out of seven native
amphibians have disappeared or declined sharply since the early
1900s.
There were some uncanny global similarities, to
these declines and extinctions— patterns that suggested
something more ominous could be taking place. The declines were, in
the first place, very rapid. They sometimes involved whole
assemblages of species, rather than just one or two. And they were
occurring not just in areas that were obviously disturbed, but in
some of the world's most carefully protected parks, such as Costa
Rica's Monteverde Cloud Forest Reserve and Yosemite National Park
in the western United States. These were not the kinds of losses
that could be readily predicted—or explained. Something
peculiar was happening to Amphibia. Habitat loss, and
pollution are clearly major factors in the decline of populations
of amphibians. But other, more subtle factors are at work,
such as increased UV radiation, the introduction of non-native
predators and reduced resistance to fungal and bacterial
disease..
Spinl's Macaw and the Mount Verde Golden Toad are
case studies of unsustainablility, touching on all the major
environmental issues of our day.