E.O. Wilson to the defense.
Look at the freshness and vigor of the organisms in the photographs on these pages and consider: No species dies of old age. Every species that disappears is killed, and it dies young, at least in a physiological sense. We still occasionally hear someone call the California condor a senescent species whose time has come. Don't hold on too tight, the prescription follows, let it go! That opinion is based on a false analogy with organisms, which compares an endangered species to a terminal patient in intensive care too expensive for society to prolong. The truth is that the great majority of such species are composed largely of young, healthy individuals, just like other, more fortunate species that are still widespread.
The condor disappeared from the wild not because its heredity declined but because people destroyed most of its natural habitat and shot and poisoned the dwindling remnant. When only a dozen individuals remained in the wild, they were captured and placed with a confined breeding colony near San Diego. Given protection and food, they and their offspring are now flourishing. If the condor habitat were somehow restored across the prehistoric breeding range and the species left alone within it for a few decades, Gymnogyps californianus would return as an abundant bird across hundreds of thousands of square miles of the American landscape.
The condor didn't change; we did. Extremely few species are dying for any reason on their own, because humanity makes the decisions of life and death at this point in geological time. Paleontologists estimate from the fossil record that before the origin of Homo sapiens, each species and its immediate descendants lived an average of between 1 and 10 million years: 6 million years in the case of starfish and other echinoderms, 1 to 10 million years for flowering plants, 0.5 to 5 million years for mammals and so on. Through most of geological history, outside rare catastrophic disturbances of the climate, the probability of extinction has also remained more or less constant through time.
Consider the following oversimplified example of such a trajectory. If one-half the species of a certain group were alive at the end of a million years, then one-half of those (or one-quarter of the original) persisted 2 million years, and half of those again (one-eighth of the original) lasted 3 million years, and so on until all or almost all were gone. The overall rate of extinction, again according to group, has averaged from one species per million to one species per 10 million each year. In the present century, biologists agree, human activity has multiplied this rate as many as 1,000 times. Furthermore, the toll is steadily accelerating. The losses caused during the next 30 years, not including the impact of earlier declines, could easily reach 20 percent of the plant and animal species of the world.
By far the most important agent of extinction is habitat destruction. All biologists know that when habitat is reduced, species disappear. The rule of thumb is that a 90-percent loss of area results in an eventual 50-percent loss of species. The rate of loss of tropical rain forest during the late 1980s was estimated to have been about 1.8 percent per year, having nearly doubled since the 1970s. That amount translates to half a percent of the species lost or doomed annually. The theoretically lowest, least destructive estimate still projects to a quarter-percent extinction per year.
As the forest is cut back, as dams fill valleys and obliterate natural stream systems, as wild savanna is ploughed under, some very localized species are extinguished at once. Others persist in populations too small to persist beyond a few more years.
How long do doomed species last in habitats fragmented too small to support them? It depends on the size of the reserve. The loss of bird species in tropical American rain-forest patches reduced to 1 to 25 square kilometers has been observed to reach 10 percent to 50 percent in the first 100 years. Animals that are sparsely distributed, specialized in their requirements and short-lived, such as certain birds and butterflies, disappear first. Tree species can last for decades or in extreme cases for centuries. But a severe storm, a fire or an errant chain saw can finish any of them in an instant.
The life of some endangered species can be extended indefinitely by propagation in zoological parks and botanical gardens. Yet only a tiny fraction can be saved in such a manner. Facilities exist for up to several tens of thousands of favored higher plants and vertebrates, but for most plants and vertebrates and, worse, for almost all the millions of insects, other invertebrates, fungi and bacteria so vital to the functioning of the natural world, there is no such refuge.
As habitat is reduced, the other three apocalyptic horsemen of extinction - pollution, overharvesting and the introduction of exotic species - come into play. The worst is the last of these. Under certain conditions, a small number of exotic species can alter entire ecosystems and diminish or extinguish indigenous species.
Local mass extinctions are being observed with increasing frequency around the world in groups as disparate as flowering plants and freshwater fishes. They often entail the extirpation of species and races found nowhere else. It is a sad rule of field biology that when ecosystems are studied carefully before and after serious human disturbance, extinctions are almost always revealed. The casualty roll includes the following:
* One-fifth of all the bird species of the world during the past 2,000 years, with 11 percent of the remaining 9,040 species currently threatened or endangered.
* More than half the 266 species of exclusively freshwater fishes in peninsular Malaysia.
* Fifteen of the 18 endemic freshwater fishes of Lake Lanao in the Philippines.
* All of the 11 endemic tree snail species of Moorea in the Society Islands. Those on nearby Tahiti, as well as on Hawaii, are also rapidly disappearing.
* Upwards of 90 endemic or near-endemic plant species from a single mountain ridge in Ecuador, through clear-cutting of forest during 1978 to 1986.
As populations are restricted in size, they lose some of the genetic varieties composing the internal variability of the species. When individual organisms become more uniform within the populations, the species as a whole loses its ability to adapt to changes in the environment. The organisms also become in effect more closely related to one another (because their genes are overall more similar). The rate of inbreeding consequently increases, which in a few extreme cases reduces vigor and fertility of individuals and renders the species as a whole still more vulnerable.
Not just species and genetic variants but entire ecosystems vanish as the natural environment is eroded. A final stand of old-growth forest leveled here or a river dammed there can erase large numbers of species in one stroke. When the last remnant of a rain-forest tract is clear-cut in the Andean foothills, to take one extreme example, we can expect to see the local demise of perhaps 300 kinds of birds; up to 1,000 butterflies; 300 ants; 50,000 beetles; 1,000 trees; tens of thousands of fungi and bacteria; and so on down a long roster of major groups. Some of the species can be expected to have been limited to that particular habitat, so their extinction will be total and final.
Each species in the ecosystem occupies a precise niche, demanding a certain location in the forest, an exact microclimate and particular nutrients and temperature and humidity cycles with specified timing to trigger phases of the life cycle. Many and perhaps most of the species are locked in symbioses with other species. They are the pollinators, root symbionts, epiphytes and other mutualistic partners, hangers-on and parasites that raise the superstructure to extreme complexity. They cannot survive and reproduce unless joined with certain other species in the correct configurations of space and time.
Each species, to put the matter succinctly, is a masterpiece. It deserves that rank in the fullest sense: a creation assembled with extreme care by genius. The master craftsman that shaped it was natural selection, acting upon mutations and recombinations of genes, through a vast number of steps over a long period of time. Each species is consequently a source of scientific knowledge and aesthetic pleasure. The number of genes prescribing an organism belonging to a higher life-form (in other words, more complex than a bacterium) runs into the hundreds of thousands; the nucleotide pairs composing them, the genetic letters that encode the life-giving enzymes, number according to species from 1 billion to 10 billion. If the DNA helices in one cell of a mouse (a typical animal species) were placed end on end and magically enlarged to the same width as a piece of wrapping string, they would extend for about 600 miles, with 20-odd nucleotide pairs packed into every inch. How all that genetic information translates into a fully functioning organism is still partly a mystery. The lesson to be drawn is that the life-forms around us are too old, too complex and too valuable to be carelessly discarded.
So far I have offered some of the facts and statistics from which scientists offer the case for conservation. Such information implies cost and benefit, the national interest, the state of the world. It is an argument primarily of the mind.
The remarkable photographs presented here have a wholly different impact. These portraits speak to the heart. In the end, their kind of testimony may count as much toward conserving life as all the data and generalizations of science. Each photograph strips the environment from the background of the animal or plant chosen to represent its species, forcing us to look at the face of the organism unadorned. We are given no opportunity for distraction. The technical quality of the portraiture is so fine, the composition so pleasing, that we gladly contemplate for a few moments creatures as strange as the Furbish lousewort (yes, at last we have a look at the plant with the fabled name) and the American burying beetle.
Each species is personalized. The freshness of the visage of the emissary chosen by Middleton and Liittschwager, the sign of a life cycle still capable of renewal, offers hope. The creature can no longer be called a weed, a flower or a bug. It has a name, a million-year history and a place in the world. It is now unmistakable and unavoidable. It is more than a statistic reduced to, say, one less warbler from the forests of North America, one less bivalve from the riffles of the Tennessee River drainage. The endangered species whose portrait we see can be a companion henceforth, if we wish, for us and for our descendants as far into the future as can be imagined. Its death we will have occasion to mourn bitterly.
RELATED ARTICLE: California Condor
"The condor disappeared from the wild," writes E.O. Wilson. "not because its heredity declined but because people destroyed most of its natural habitat and shot and poisoned the dwindling remnant." By 1987, only 27 of these largest flying birds in North America survived, and all were in captivity. Attempts to release the birds have met with mixed success, but researchers are now training the birds to avoid hazards such as live electric wires. As of this writing, six condors had survived a release last winter, and more releases were being planned.
RELATED ARTICLE: American Burying Beetle
Once found in 32 states, this victim of DDT contamination is found only in Oklahoma and on a New England island (wildlife officials keep the location vague to deter collectors). The beetles live up to their name, burying found carcasses of birds, rodents and other small animals, in which they carve space and lay eggs. Both parents tend to the larvae, which munch on the walls of their home.
RELATED ARTICLE: Furbish Lousewort
Without its odd moniker, this perennial herb surely would not have become well known outside of Maine, where it was imperiled by plans for a dam in the 1970s - and now is at risk from development. The plant grows along the St. John River, where spring runoff scours away rival vegetation. Seven lousewort stands were discovered in 1976. At last estimate, 5,000 individuals plants were growing along the river in Maine and Canada.
RELATED ARTICLE: Jaguarundi
Though a few wild jaguarundis may still exist in the extreme southern tip of Texas, this elusive housecat-sized feline probably exists in the United States only in captivity. The cat's decline is likely due to eradication of its scrub habitat for farming and grazing in southern Texas and southeastern Arizona. Jaguarundis do survive in the wild in Mexico, where they inhabit dense brush mixed with grassland.
RELATED ARTICLE: New Effort To Save Species
With funds set aside specially for working on behalf of endangered species, NWF has developed an ambitious new effort to help communities in conservation of imperiled animals. The plan includes grass-roots education and legislative advocacy work. See "The NWF View" on page 6 for details. For more information and a free pamphlet on endangered species, call 1-800-824-WILD.
RELATED ARTICLE: Flattened Musk Turtle
Named, yes, for its flatness, this water-loving turtle may find its shape useful for wedging itself between rocks or into a crevices. A denizen of Alabama's major coal region, it is at risk from toxic runoff that contaminates food sources in streambeds. In a more immediate threat, dams to create lake's along the state's Black Warrior River system have left the turtle's food supply of mollusks choked by slit.
RELATED ARTICLE: Northern Aplomado Falcon
As the grasslands of the U.S. Southwest have been grazed or converted to crops, the northern aplomado falcon has lost both habitat and prey. Pesticides, particularly DDT in the past, have also taken a toll. Though it once nested in Texas, Arizona and New Mexico, this species no longer breeds in this country. It can still be found south of the Mexican boarder, and U.S. reintroduction efforts are underway.
A Pulitzer-prize-winning writer, entomologist E.O. Wilson teaches at Harvard University and is the author of numerous books, on subjects ranging from ants to sociobiology. His most recent solo effort was an autobiography, Naturalist (Island Press, 1994). California photographers Susan Middleton and David Liittschwager collaborated on their book Witness: Endangered Species of North America (Chronicle Books, 1994), from which Wilson's essay is adapted.
|Printer friendly Cite/link Email Feedback|
|Title Annotation:||biologist fights for the protection of endangered species|
|Author:||Wilson, Edward O.|
|Date:||Dec 1, 1995|
|Previous Article:||How NWF is defending out natural heritage.|
|Next Article:||The benefits of badgers.|