COLUMN ONE : Extinction of Planet’s Species : Scientists predict millions of plants and animals will soon be wiped out if destruction of wild land continues. But most believe the trend can be reversed.
The year is 2050. As many as half of the planet’s species have either vanished or dwindled to numbers too small to assure them a long future.
Large animals such as giraffes live only in scattered preserves and zoos. Their survival depends on stored embryos, sperm and eggs that have been frozen for future breeding.
Greenery persists. So does wildlife. But there is a sameness to the landscape. Only those plants and animals that coexist well with humans have survived in large numbers. “Weedy species,” including rats, starlings and cockroaches, have thrived.
This pessimistic vision, drawn from interviews with many highly respected scientists, represents their predictions for the future should wild lands, particularly tropical rain forests, continue to vanish at current rates.
“This is not something off in the indefinite future,” said Jared Diamond, professor of physiology at UCLA. “This is something that is going to reach its climax in the lifetimes of the kids who are being born now.”
Many researchers--even a minority who believe the crisis will not occur for a century or more--generally agree that Earth is approaching or already has entered a major extinction spasm, one of just a handful in the planet’s 4.5 billion-year history.
Entire ecosystems or landscapes could disappear. Genes important to medicine and agriculture would be lost. Soil productivity and hydrological cycles would be disrupted.
Key to the problem is worldwide population growth. In the past 40 years, human population has more than doubled to 5.4 billion and may more than double again within a century. Pressures to destroy what natural settings remain will multiply.
Potential global warming caused by emission of man-made gases could be a particularly devastating blow to wildlife, but the situation would be grim even without it, scientists say.
Fortunately, even the pessimists believe the losses can be stemmed. In an important first step globally, many of the world’s nations have been negotiating a treaty intended to spur conservation of the planet’s biological diversity. The accord, if completed, would be signed at a June meeting in Rio de Janeiro.
But for now, the trends are ominous. Nobody even knows exactly how many species are being lost because nobody knows exactly how many species exist.
At least half of all plants, animals and other organisms are believed to live in tropical rain forests, which occupy only 6% of the world’s land. About 40 million acres of these teeming forests vanish each year, cleared for farming, cattle grazing and timber, primarily in West Africa, Southeast Asia and South America.
“I would say that if we do not halt the ongoing destruction of natural habitats, we will have lost 20% of the species now living in the next 30 years,” speculates E. O. Wilson, a biologist at Harvard University.
Scientists generally put the total of species worldwide at 10 million, but estimates range from 5 million to 100 million, most of them insects, other small organisms and microorganisms--such as bacteria--not yet discovered.
Taxonomists have named only about 1.4 million species, including 4,000 kinds of mammals, 9,000 birds, 250,000 plants and 750,000 insects.
Daniel Simberloff, a professor of biological science at Florida State University, estimates that more than half of the world’s species will be doomed by the middle of the next century unless drastic action is taken.
The alarm comes from tropical researchers who have witnessed the rapid disappearance of wildlife and from studies showing that, as a rule, 50% of species are condemned once 90% of their tropical forest habitat is removed.
Scientists cannot predict with any certainty how quickly extinctions occur once habitat is destroyed. But when one species is lost, they say others will vanish with it.
Researchers in the Amazon observed the web of life unravel after a rancher, at the scientists’ request, allowed patches of rain forest to remain in an area that had been cleared in 1979 for cattle.
Pigs disappeared from some of the isolated patches, triggering the demise of seven species of frogs, according to one of the researchers from the Smithsonian Institution. The frogs needed the pigs’ wallows to survive.
Some species of birds also disappeared because they were dependent on army ants. The patch of forest was too small to sustain enough swarms of the voracious ants, which scare up insects from among the leaves and under logs as they approach. The birds survive by feeding on the insects fleeing the ants.
“There are just hundreds of ways in which individual species depend on other species,” said Simberloff. “ . . . I’m sure we are going to get a lot of unpleasant surprises.”
As some species dwindle, others that adapt easily to different environments will flourish to fill the vacuum.
“It’s the most persistent species that will survive this, and many of them are pests of our most important crops and timber resources,” said Dennis Murphy, director of the Center for Conservation Biology at Stanford University.
Even if wholesale extinctions of wildlife can be staved off, the numbers will still be sharply reduced, limiting the chances of survival over the long term, scientists say.
“We will save a lot of species,” said Michael Soule, chairman of the environmental studies department at UC Santa Cruz, “but we will have to be content with them being literally frozen for a while or in captivity.”
Although much of the lament over vanishing wildlife focuses on tropical forests in developing nations, the industrialized world has little to boast about.
The United States, for instance, has been destroying its virgin old-growth forests more rapidly than tropical forests are being lost globally, according to Simberloff. Only 13.5% of the nation’s rain forests remain and only a third are left in Canada, he said.
Despite the grim trends, a minority of scientists believes that a major extinction crisis is not at hand. They complain that extinction studies, often conducted on islands, exaggerate the losses because many continental species can escape into bordering areas once their prime habitat is removed.
“Think of fighting a fire,” says Michael Mares, director of the Oklahoma Museum of Natural History and a University of Oklahoma zoology professor. “ . . . I see the fire as beginning but not as the raging conflagration that some people see.” Mares notes that “not everything is being converted into parking lots,” and many species might be able to survive in secondary forests and grazing lands.
Skeptics point out that only two forest birds were lost as a result of the deforestation of the Eastern United States. But other scientists say tropical forests contain substantially more species than did the Eastern United States, and many cannot survive outside small ranges. Another example offered by skeptics is Puerto Rico, a tropical island that lost most of its virgin forests at the beginning of the century and did not suffer massive extinctions. But the island is regularly buffeted by hurricanes and its species have evolved to adapt to tremendous disturbances.
The resiliency of nature is hard to factor in the extinction projections.
“I was born in West Virginia in the country, and as a boy I never saw a white-tailed deer,” said Lloyd Kiff, an ornithologist and director of the Western Foundation of Vertebrate Zoology, a research and conservation organization in Southern California.
“Pileated woodpeckers were nonexistent. Yet the deer are now a menace in the state, and the woodpeckers are coming to people’s back yards. Nobody would have predicted this in the 1940s.”
What happened? The forests regenerated as subsistence farming declined, and the deer, which tend to thrive in disturbed habitat, rebounded as hunting decreased.
While Harvard’s Wilson estimates that 50,000 species are being doomed each year in rain forests alone, Mares is one who contends that the crisis may still be a century or more away.
“I’m saying we’re losing those (50,000) species every 20 or 30 years, but it is still quite a few when you look over normal geological time, which is millions of years,” Mares said.
Major extinction spasms are rare, even over geological time. The only significant extinction episode triggered, at least in part, by man occurred 10,000 to 12,000 years ago when many large animals vanished from the planet.
Until that time, mastodons, elephant-like creatures, roamed the United States. So did giant ground sloths--long-clawed, bear-like animals--and lions, camels, native horses and saber-toothed cats.
“We are losing more species now, but the flagships, the really dramatic examples of what’s at stake, are already lost,” said Paul S. Martin, emeritus professor of geoscience at the University of Arizona in Tucson.
Martin believes that man probably hunted North America’s large mammals to extinction. Africa and parts of Asia have similar creatures today only because disease and rugged terrain limited human population, he said.
Simberloff’s research has found that if extinction studies are correct for continents as well as for islands, today’s losses would be closer in scale to the demise of the dinosaurs 65 million years ago, a massive extinction spasm that dwarfs the later disappearance of large mammals.
An estimated 60% to 80% of species vanished along with the dinosaurs, possibly after Earth collided with an asteroid. Millions of years later, large mammals evolved from animals the size of rats and squirrels to fill the dinosaurs’ niche.
“For those who say that extinction is natural and we can just wait for nature to replace them, well 10 million years is a long time to ask our descendants to wait,” said Wilson of Harvard.
A United Nations agricultural organization already is sounding the alarm, promoting the collection and conservation of plants from around the world. At stake is the world’s future food supply.
Plants, like other life, contain a multiplicity of genes. These genes can be used to breed crops that can resist disease, climate change and pests. When diversity is lost, crops become more vulnerable.
Food sources already are dangerously homogeneous. Early man lived off several thousand plant species but people today cultivate only 150 species. Much of the world depends on no more than 12 plants for food.
Recent history underscores the hazards of such a trend. In the 15th Century, a few potatoes brought from Peru eventually led to extensive cultivation of the crop in Europe.
When disease struck the genetically alike potatoes in the 19th Century, the crops quickly succumbed and millions starved in Ireland, where the vegetable had become the staple of the diet.
Researchers returned to Peru and discovered potatoes of all colors and shapes. Some were bred with the European variety to make it immune to the scourge.
“New diseases will appear because microorganisms are always evolving,” said Jose Esquinas-Alcazar, secretary of the U.N.’s Food and Agriculture Organization. “So new varieties will have to be developed every so often.”
Just in the past few years, a new kind of aphid that kills wheat appeared in the United States and elsewhere. Plant explorers are going into the Ukraine and Turkey to obtain genes from almost extinct wheat varieties to breed commercial crops capable of resisting the pest.
Mindful of the dangers, governments around the world have stored more than 2 million samples of seeds and plant tissues.
But storage cannot substitute for conservation. In poor countries, some samples have been lost because of an inability to pay for air conditioning. What is reputed to be an excellent collection in Eastern Europe is being threatened by the economic crisis there.
Moreover, small samples stored in a bank cannot replicate nature. In the wild, plants continually evolve, adapting to new environments and developing new characteristics.
“When you put them in a gene bank, you are freezing evolution,” said Esquinas-Alcazar, a geneticist and professor at the University of Madrid in Spain.
The destruction of natural settings, particularly tropical forests, also is ominous for medicine. Plants produce an array of secondary compounds, many of which have ultimately been developed into pharmaceuticals.
Tropical plants are especially important because they contain diverse chemical defenses to protect them against their many predators. Insects too are believed to be a still largely untapped source of drugs.
To avert catastrophe on all fronts, policy-makers, scientists and conservationists have developed a long shopping list. Even some of the more pessimistic scientists believe that strong and quick action could save a lot.
“If we take strong action,” says Wilson, “we can hold (the losses) to 10% or less” over the next 30 years.
The list of potential solutions is predictable. It includes more reserves and botanical gardens, more genetic storage in banks, improved family planning programs, more funding for scientific research to identify and conserve remaining wildlife and greater technical and financial assistance to developing countries.
The proposed biological diversity treaty calls for many of these measures.
But carrying them out globally would cost billions of dollars during the rest of this decade, and negotiators have weakened requirements for specific conservation measures by various nations.
Conservationists believe that strapped developing nations must be given a financial incentive to conserve their forests. In the past, developing countries have not earned profits from their wildlife even when it has been the source of commercially successful chemicals, drugs and agricultural improvements.
Finding a system to allow for shared benefits has proved difficult. Industrialized countries, citing patent laws, say they cannot just hand over proprietary technologies in exchange for access to tropical forests.
But many scientists say cost is not ultimately the problem. Rather, it is a lack of will.
“I think we are just at the edge of people beginning to focus on it,” said Peter H. Raven, director of the Missouri Botanical Garden and home secretary of the National Academy of Sciences. “By the end of the ‘90s, people will be deeply concerned about the loss of diversity.”
The next 30 years are expected to be the most telling. Population is projected to rise by 100 million a year, with 90% of the increase in developing nations, home to most of the tropical rain forests.
“The die will pretty much be cast by the middle of the next century,” said Murphy of Stanford.
Why Animals go Extinct
here are the major reasons that species become extinct: MAMMALS: Habitat loss: 19% Over exploitation*: 23% Species introduction: 20% Predator control 1% Other: 1% Unknown 36%
BIRDS: Habitat loss: 20% Over exploitation*: 11% Species introduction: 22% Predator control 10% Other: 37%
REPTILES: Habitat loss: 5% Over exploitation*: 32% Species introduction: 42% Unknown 21%
*Includes commercial, subsistence, and sport hunting and capture for zoos, research and sale of pets.
On the Earth
Here is a look at the estimated number of species in several taxons, or categories, of creatures: Insects: 751,000 Plantae (multicellular plants): 248,428 Non-insect Arthropoda (mites, spiders): 123,161 Mollusca (Mollusks): 50,000 Fungi: 46,983 Protozoa: 30,800 Algae: 26,900 Pisces (Fish): 19,056 Platyhelminthes (Flatworms): 12,200 Nematoda (Roundworms): 12,000 Annelida (Earthworms): 12,000 Aves (Birds): 9,040 Coelenterata (Jellyfish, corals): 9,000 Reptilia (Reptiles): 6,300 Echinodermata (Starfish): 6,100 Porifera (Sponges): 5,000 Monera (Bacteria, blue-green algae): 4.760 Amphibia (Amphibians): 4,184 Mammalia (Mammals): 4,000 Source: Annals of the Entomological Society of America, World Resources Institute, 1989.
