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Habitat Change, Population Growth, and the Biodiversity Crisis: Getting Ahead of the Extinction Curve (1)

by Daniel Simberloff

The Extinction Spasm

No one can tell you exactly how many species are going extinct every year, just as no one knows exactly how many species there are on earth. About 1.4 million species have been described by scientists, but the most recent expert estimate is that there are actually between 5 and 8 million species. Many of them are things you wouldn't get very excited about, like beetles or small plants or mites or worms. But there are still a lot of unknown species out there in groups that interest us a lot.

Even new mammal species are frequently discovered. Just in the last five years at least three new monkey species and two new hooved animals were discovered, and not all these were in remote places. One of the monkeys is found only 40 miles from Sao Paolo, Brazil, and one of the hooved animals is in Vietnam. A new whale was discovered in 1991.

Of course, no species is immortal, and extinction goes on all the time. Probably about a billion species have existed at one time or another since life first evolved on earth around 3.5 billion years ago. Obviously the vast majority of them have gone extinct. Some extinction must happen on a fairly regular basis. This ongoing extinction is called "background" extinction, but its rate is very low. Some people have estimated it at around five species per year. Every so often, at least five times during the last 250 million years, there is a mass extinction, with hundreds of thousands of species going extinct in a relatively short time. The last major extinction of this sort was at the end of the Cretaceous period, about 65 million years ago. This included the end of the dinosaurs that had dominated land. It is possible that this extinction was caused by the impact of a meteorite, or there might be other causes, but whatever happened, many thousands of species went extinct in a few centuries at most.

We are in the midst of a mass extinction right now, one that began less than two centuries ago. There have been about ten authoritative studies in the last few years, and these give a minimum current rate of extinction of about two percent per decade, or at least 10,000 species per year. This figure would put us right in the range of the great prehistorical mass extinctions.

What do these extinctions mean to us? Many people would say that it is unethical to eliminate species, and that humans have no particular right to make the planet unable to support other kinds of beings. There are many recent books and articles by ecologists, philosophers, and even clergy that generally support this view. In my mind, none of these writings is convincing because ethics is a slippery concept. It is very hard to convince someone that his or her ethics are wrong and yours are right. Also, I think it is obvious that ethics play a very small role in decision-making that determines the fate of species or entire ecosystems. I am not saying that the ethics of conservation should not be important; I'm only saying that they don't seem to be important yet and that attempts to make them important haven't been very effective.

Instead of focusing on ethical questions, I am going to concentrate on the economic costs of extinctions. It is difficult to know exactly how much the current extinction spasm is costing us, especially because some of the benefits of these species would have been realized in the future. Just pharmaceuticals derived from plants are now worth about $40 billion per year, and fewer than 1 in 100 plants has been surveyed for phytochemicals that might turn out to be medically useful. Just one plant that stops cancer, like the rosy periwinkle, can be worth over $200 million per year. It is the treatment of choice for Hodgkins' disease and some lymphomas. About 1 in 5 people in the U.S. and the rest of the world eventually contract some cancer, and for many of them there are still no known cures.

It is ironic that, in the last ten years, it has become possible for the first time to take a gene from one species and put it into another. One can even put a plant gene in an animal or vice-versa. This leads to staggering possibilities. It may even be possible to replace a defective gene in humans with a gene from another species, for example. It is already possible to take a gene creating a useful product from a slow-growing species and put it into a fast-growing species to get much more of the product. For example, human interferon is already being produced by trees, and several useful genes from plants have been put in bacteria that make their products much, much faster.

We cannot actually synthesize a new gene from scratch, and making new genes isn't even on the near horizon. So we are limited to whatever genes exist in nature now, and every species is a library of genes. The number of genes ranges from a few thousand in bacteria and fungi to around 100,000 in the typical mammal to half a million in some plants. At exactly the time when we have learned to use this library, we are destroying it at the rate of at least 10,000 species per year and probably much faster. This is what is so ironic.

Species are used for many things besides medicines. They are used for foods, of course, but surprisingly few species have been tried. For example, out of more than 14 million plant species, only 3,000 seem to have been seriously tried as human food, only 200 have been domesticated, and only 20 are major crops. Yet evidence from food use by different cultures shows that there are many more possibilities, and some of these plants are easier to grow and healthier to eat than the commonly used ones. Yet we are destroying them. For example, there are two species of perennial corn, and both are threatened with extinction in the wild in Mexico. Just think of the possible economic and environmental benefits of putting a gene for perenniality into corn.

Plants also are used for fuel, and this is a use that will have to increase as fossil fuels are depleted. Brazil already generates 28 percent of its energy needs from sugarcane biomass, and saves over a billion dollars annually on oil imports. Again, the plant kingdom has been very scantily surveyed for potential fuel use of individual species or their genes, and we are destroying thousands of possibly useful plants each year.

There are innumerable other uses of plant, animal, and microbial species. Just as one example, plant species already provide an enormous service to humankind by removing excess nutrients from the environment and converting them into biomass. There is a lot of promising research on microbes that literally eat oil and other chemicals, and so could potentially alleviate some major pollution problems.

In addition to the value of individual species, intact ecosystems provide many services to humans. They prevent floods, cleanse water, produce oxygen. These services are worth many billions of dollars in the U.S. alone. The exact role of individual species in maintaining sufficient integrity of entire ecosystems that perform these services varies from system to system, and is also not well studied. This leads to the notion of "substitutability." Would it not be possible to maintain these ecosystem services even as we eliminate biodiversity by simply substituting a few common species for the myriad rare ones. Even the preliminary study that ecologists have given this matter shows that particular single species can have an enormous influence on the maintenance and function of an entire ecosystem.

Just as one example, consider the longleaf pine forests that originally dominated the Southeast. They used to cover at least 70 million acres from Texas all the way to the Atlantic Ocean. They were virtually all cut down in the late 19th and early 20th centuries, and largely replaced by farms or by slash and loblolly pine tree farms. Slash and loblolly produced new crops of trees very quickly, so they were replanted. However, the second and third crops have been very disappointing, disasters in some places. They have grown very, very slowly. No one knows exactly why, but nutrient depletion probably has something to do with it. In any event, the wood of even the first crop of slash and loblolly pine is nowhere nearly as good as longleaf wood. Slash and loblolly are basically pulp for paper, while longleaf is used for building, shipmasts, and other things. It is much more valuable than wood of the other pines. Furthermore, as people came to be interested in biodiversity for its own right, they came to realize that planted slash and loblolly pine forests were virtual biotic deserts compared to longleaf. Old growth longleaf pine groundcover has about 500 species of plants, many not found anywhere else, and many species of animals that are highly adapted to it. The trees themselves are used by one of the most famous endangered species, the red-cockaded woodpecker. The decline in this bird is caused by the decline in longleaf forests.

So, both for the value of the wood and for the diverse threatened plants and animals, people are trying to restore longleaf forest. It is turning out to be very difficult, for reasons that one would not have expected. First of all, the key groundcover plant in longleaf forest, wiregrass, was completely extirpated when the land was logged and cleared, and it didn't grow back, because it grows largely by stolons rather than by dispersing seed. Rather, it was replaced by other plants. These other plants not only don't support the diverse animal community that wiregrass does, but they don't carry the fires as well that are critical to longleaf pine. These forests used to burn naturally from lightning strikes every two or three years, but now that they are in tiny fragments, the fires don't spread and each fragment is unlikely to be hit by lightning. Even when fire does start in a longleaf fragment, it doesn't spread well and burn with a cool, non-destructive fire unless there is a thick wiregrass groundcover. Without regular fires, the longleaf pine itself is quickly overgrown by hardwoods and the entire longleaf-adapted animal community is lost. Also, it turns out that longleaf doesn't grow well unless it is inoculated with a symbiotic root fungus that helps it to take up nutrients from the soil, and the animal that did the inoculation was the fox squirrel, which is now a threatened species, and completely missing from many areas, because of the destruction of longleaf pine forests. So, all in all, the maintenance and function of this entire major community seems to require the presence of two species -- wiregrass and the fox squirrel -- that one probably wouldn't have thought were important until we saw what happened when they disappeared.

Causes of Extinction

Virtually all extinctions today are caused by human activities. It is impossible to point to a recent extinction or even an endangered species where one can say the decline would have happened anyway if humans had not been around. In fact, the main cause of extinction today is habitat destruction and fragmentation. For instance, habitat destruction caused the extinction of at least 68 of 116 recent extinctions of birds, and is the problem for 117 of 149 well-studied threatened bird species. This is well-known, but the pervasiveness of habitat change and the pernicious ways it can work are among the most active areas of research in conservation biology.

Obviously when one completely destroys a habitat, such as leveling a forest, all the species in it will disappear. There is a rough relationship between the area of a site and the number of species in it that gives a ballpark estimate of the amount of local extinction that a decrease in area will cause. It is becoming clear that, even if there is substantial total area of some habitat left, if it is divided up into sufficiently small and isolated fragments, many species will be in trouble. Yet this is exactly what has happened over the past few centuries to virtually every habitat on earth -- increasing fragmentation. The classic study was done in the U.S. on forests in southern Wisconsin, but the same story is repeated over and over throughout the world.

Many different things can happen in a fragmented landscape that make it hard for species to survive, and some of them are very subtle. One very common thing that happens is that there is increased predation or herbivory on the residents of the fragments by species that live in the surrounding matrix. As one example, a biologist named David Wilcove put artificial nests with birds eggs in eastern forest fragments of different size. He found that in the largest fragment, the Great Smoky Mountains National Park, there was virtually no predation on these eggs. In the typical woodlots of 20 acres or so, virtually every nest was preyed on within a week. The predators were dogs, cats, raccoons, crows, squirrels, and jays. These are all species that are very common in the variegated suburban and agricultural landscape that dominates the eastern U.S. nowadays, but are not at all common in very large tracts of unbroken forest. This may be one of the big problems for declining neotropical migrants that we read about so much these days -- they tend to have open, cupped nests.

This same principle holds for plants. For example, in northern Wisconsin, the forest originally comprised about 80 percent of old-growth hemlock, cedar, yew, and other trees, with small fragments of early successional stage trees like aspen. Now the situation is exactly reversed, with about 90 percent regenerating lands dominated by aspen and about 10 percent old-growth, scattered in fragments of 20-400 acres. The U.S. Forest Service would like to maintain these fragments as old growth, because many plants and animals live in them that don't live in the aspen. But they are finding that these old growth fragments are changing in spite of their efforts. The old growth plants are not replacing themselves. The reason is that deer populations are very elevated in the aspen-dominated young forests, but they forage preferentially in the old growth fragments on the seedlings of old growth trees. Now it seems that, in order to save old growth, it will be necessary to set aside very large tracts, of tens or hundreds of square miles.

Global warming will interact with habitat fragmentation to cause extinction sometime in the next century. There have been periods when the earth warmed in the past, but these were not associated with mass extinctions because the geographic ranges of both plants and animals simply retracted northward. Most American trees moved north at the rate of about 15 miles per century during the last warming. Some plants are now found only hundreds of miles north of their ranges during very warm periods. Such migration was probably no big deal then; the climate changed relatively slowly and forests were continuous. But think about the problems nowadays. A forest refuge in North Carolina, for example, is likely to be at least 100 miles from the nearest forest refuge to the north, and the land in between is farms, shopping malls, and houses. So there is no way for a plant to move north year after year by having seedlings dispersing slightly to the north thrive. Even forest animals would have a hard time moving between two refuges 100 miles apart.

The second biggest cause of extinction is introduced species, and these cause extinction in many ways. Probably the most common is by habitat destruction. Introduced grazers destroy the native plants and the animals that live in them, or introduced plants simply out-compete the native plants and completely change the ecosystem.

Introduced species wreak havoc by many other means. For example, the entire lowland Hawaii bird fauna is introduced, and the native birds are all threatened. Many have already gone extinct. Among the causes of their extinction is bird pox and bird malaria, carried from the introduced birds by introduced mosquitoes. Another cause is the replacement of the native forests to which they were adapted by introduced plants that they can't use.

With increasing commerce and travel, the problem of introduced species is accelerating in spite of regulations to keep people from moving living organisms around. There are just too many exceptions to the regulations, and inspection can't begin to do an adequate job on the explosion of planes and ships traveling around the globe today.

The third biggest cause of extinction is hunting or other deliberate harvest, such as by animal or plant collectors. The rarer a species gets, the harder people try to collect it, and eventually the species disappears entirely. There are many examples, but habitat destruction and introduced species each cause at least twice as much extinction as various forms of harvest.

The Ultimate Causes of the Problem

In 1967, Lynn White, a historian, published an extremely important paper laying out one of the key causes of the environmental crisis. He pointed out that both modern science and modern technology are Western. Technology has absorbed elements from other areas, especially China, but technology and science today, even in Japan and Nigeria, are fundamentally the descendants of phenomena that began in the West. This dominance of the West in both science and technology is much older than the Scientific Revolution of the 17th century. By the year 1000 the West began to harness water and wind power, which led inexorably to various labor-saving devices and to automation. By the 15th century Europe was so technologically superior that its little nations could spill out over the rest of the world, conquering, looting, colonizing, and spreading its species. Even Portugal, one of the weakest Western states, was able to rule the East Indies and Brazil for a long time. These technological advances led to societal and agricultural changes that permitted the exponential growth of the human population, which I will discuss in a moment.

Since all this began in the Middle Ages, we have to look to medieval European assumptions and conceptions of nature and its relationship to humans. First is a belief in perpetual progress that was unknown to the Greeks, the Romans, or in the Orient. This notion of perpetual progress is rooted in Judeo-Christian teleology -- human existence is destined to get better and better and better. Just what did Christianity tell us about the relationship of humans to their environment? It told us that God created light and darkness, heavenly bodies, the earth and all its plants and animals. Finally, God created Adam and Eve, and He created all the rest of nature to benefit humans, who were created in God's image. Humans were to have dominion over fish and fowl and field and forest. All these other species were there only to serve humans.

Gradually this view of human dominance over nature became embedded in attitudes of all Western nations. Nature was a machine created by God to serve humans, and God intended us to use it to its fullest. One sees this attitude in every aspect of the environmental crisis, although assumptions of this sort are often not explicit and are very rarely questioned.

Just as one example, consider what the word "conservation" means in the U.S. It was coined in this country in the late 19th and early 20th centuries, and the definition was the outcome of a battle. Leading one faction, the losing one, was John Muir, the naturalist, author, and founder of the Sierra Club. Leading the winning faction was Gifford Pinchot, America's first professional forester and later chief of what became the U.S. Forest Service. Pinchot actually coined the term "conservation" and he defined it in 1910 this way:

The first principle of conservation is development, the use of the natural resources now existing on this continent for the benefit of the people. In the second place, conservation stands for the prevention of waste. There is a third principle. It is this: The natural resources must be developed and preserved for the benefit of the many, and not merely for the profit of the few."

This quote really says it all. Pinchot was very much a man of his times, dominated by the exuberant spirit of a huge young country just becoming aware of its power, and dedicated to opening up and using the frontier. Small wonder that Pinchot's view of conservation prevailed. Note also that the first and foremost element of his definition of conservation is development, which nowadays we often think of as the antithesis of conservation. Notice that the key is to use it, but to use it wisely, that is, without wasting it. Pinchot abhorred waste; to him, cutting down a forest for paper was fine, but cutting it down in such a way as to leave lots of wood and slash to rot on the ground was a crime. His concern for waste was understandable. In those days in the Southeast, for example, people used to clear land for farming by girdling all the trees and letting them die. Notice finally that only his last principle even mentions preservation, and even there it is tied to development. In modern terms, Pinchot would not be viewed as a conservationist. His phrase, "wise use," is the banner of the wise use movement that has arisen in the U.S., especially in the West among ranchers and loggers, to oppose what they see as the excesses of the conservation movement. Most conservationists today view them as anti-environmentalists.

John Muir was a generation older than Pinchot and had very different views of conservation. He wrote:

Any fool can destroy trees. They cannot run away; and if they could, they would still be destroyed. It took more than three thousand years to make some of the trees in these western woods . . . God has cared for these trees, saved them from drought, disease, avalanches, and a thousand straining, levelling tempests and floods; but He cannot save them from fools -- only Uncle Sam can do that."

Muir did not see humans as the rightful masters of nature, to be served by other species. He viewed humans as part of nature, and thought nature should be protected from excesses of humans. He also wrote eloquently of ways in which many species are linked together in intricate chains of interaction that can easily be broken by ignorant destruction of part of the chain.

Muir lost in the original American debate about conservation. His main legacy was a small conservation movement that didn't really start to take off until Rachel Carson's 1962 book, Silent Spring, sensitized Americans to the destruction being caused by pesticides and began a new conservation movement. So Muir was ahead of his time in understanding the science of ecology, and 50 years ahead of his time in his conception of the place of humans in nature. As with many people who were ahead of their time, he didn't have much effect in his lifetime.

Gifford Pinchot had a huge impact, on the other hand. His conception of conservation dominated the federal and state governments until very recently. The Forest Service, of which he was first director, was placed in the Department of Agriculture because forests were viewed as tree-farms, to be grown and harvested just as corn and wheat are. They are still viewed as that in many schools of forestry. It is only recently that the U.S. Forest Service has begun to consider a forest as an ecologist would -- as an ecosystem containing many species of plants and animals, with many ecological processes necessary to maintain the integrity of the whole.

There is generally a very fundamental shift in attitudes now taking place with more difficulty in the U.S. than in Western Europe. After all, the U.S. is a huge country, and until recently we had many frontiers. There is still a lot of land here; it is not nearly as crowded as Europe. France, for example, is one of the biggest European countries and has one-fourth the population of the U.S. on only 6 percent of the land area. Furthermore, the U.S. is dominated by a "can-do" spirit. Even more than the rest of the world, Americans think that they and their technology can solve any problem.

Finally, America is more dominated than the rest of the world by the idea of individual freedom and private property rights. It is the land of "free enterprise." This includes freedom to act as one wishes unless there is a very compelling public interest that would be harmed. A very fundamental sense of individual freedom in the U.S. is freedom to do as one wishes with land that one owns.

When Paul and Anne Ehrlich wrote The Population Bomb in 1968, it immediately galvanized environmentalists because its logic seemed devastating. As Malthus had shown about two centuries earlier, population grows exponentially, but the earth has only finite capacity to support the human population, so somehow and at some time, death rates are going to equal birth rates. The Ehrlichs pointed out that increasing people used increasing amounts of resources and spewed increasing amounts of pollutants into the environment, thus exacerbating all sorts of environmental problems, including the loss of biodiversity.

The Ehrlichs were correct in their approach, but two main things happened to cause the timing of the crisis to be different than they expected. First, population growth slowed down slightly. Overall, population growth peaked at 2 percent in the 1960s and fell to 1.7 percent in the late 1970s. This is a big difference. It means that the population will probably be about 10-15 billion in the year 2100, instead of 33 billion as would have been the case if the 1960s reproductive rate prevailed.

Of course there is still a big problem -- at least twice as many people by the year 2100 as we have now, and the growth is greatest in the places that can least afford it. Ninety-five percent of the projected population growth will occur in the Third World where population is growing at many times the rate in the U.S. and Western Europe. The population of Botswana is growing at 4.8 percent per year, while the United Kingdom, Denmark, and Hungary aren't growing at all. Asia will account for half the total, and Africa for a quarter. In terms of present populations, Asia will have 2.5 times its present population, Latin America will have 3.5 times its present population, and Africa will have 5.5 times its present population. It is hard to believe that these continents can support this many people except in utter misery, when many of their nations can't support their current population.

The other thing that happened to defer the inevitable reckoning as population grows is various technological fixes. Food output over the past 30 years in Third World countries grew by 2.9 percent annually. Of course almost all of it was taken up by the growing population, but there was a real increase of 0.5 percent annually per capita. There is certainly room to increase production still further, more by intensification on existing agricultural lands than by increasing the land devoted to food production. Of course, agricultural intensification rests to a large extent on great increases in both fertilizer and pesticide use, and these are among the biggest pollution problems already.

In the 1970s and 1980s, there was a backlash against environmentalists who advocated population control, and especially against people who pointed out that most of the population growth was in Third World countries. They were accused of being racists, because the populations that were growing fastest and would have to be controlled the most were not Caucasian. They were accused of being hypocrites, because the United States and Western Europe had developed precisely because they had used their own resources so heavily that some were totally exhausted, and had even used many of the resources of the Third World. Many foreign leaders asked why they should be asked to bear the brunt of reversing the world's environmental decline, at the cost of their own economic development, and why they should be relegated to long-term second-class nationhood, just because they got started on efficiently trashing the environment later than the U.S. and Europe did.

One can easily understand this reasoning. It is certainly true that, for all that we hear about the destruction of tropical rain forest, it has not been destroyed to nearly the extent of temperate rain forest, or longleaf pine forest. Even more remarkably, up until just three years ago, when a federal judge put some logging in the Northwest off limits to protect the spotted owl, American rain forest was being cut at a faster rate than tropical rain forest. So the charge of hypocrisy is easy to understand.

There is no real answer to this, other than to clean up our act ourselves. The Third World countries are right; if we care about saving the earth's environment, we are the ones who should largely pay for it. The Ehrlichs put this in sharp focus in some recent research. They point out that the total impact of a new baby on the environment over its whole lifetime is proportional to the per capita consumption of resources This means that the impact of one child is largely a function of how much technology, like electricity use, goes into the production of things that the newborn consumes through life. Using this equation, the Ehrlichs calculated the per capita impact on the environment for newborns in every country. As might be expected, the U.S. was the worst; a newborn in the U.S. today can be expected over the course of his or her lifetime to degrade the environment far more than even a newborn Western European. The countries in which newborn babies have the least expected lifetime impact on the environment are all poor. The winner is Bangladesh, leading to the definition of a new unit of environmental degradation, the Bangladeshi equivalent. An American baby costs the earth's environment at least 40 Bangladeshi equivalents. That is, from the standpoint of environmental health, the birth of an American baby is a great tragedy, while the birth of a Bangladeshi baby is a relatively innocuous event.

So one has to conclude that it is hypocritical for an American environmentalist to say that the solution to the earth's environmental crisis is to cut down on population growth, particularly in those regions where population is growing fastest.

What Can Be Done?

All this is pretty depressing stuff, because the problems are so large and pervasive that it is easy to feel hopeless. Almost all ecologists are very pessimistic about the prospects that things will really get better, at least until they get a lot worse first. That is exactly how I feel. Not that it is impossible, but that it will be very difficult to avoid a massive extinction and further environmental decline. If we really did want to deal with it, there are some things we would have to do.

First, even though we have to be cognizant of global dynamics and the global dimensions of the environmental crisis, we have to act largely on a local level. So the old saw (well, new saw) is correct: "Think globally, act locally." We will never even have a chance of solving the problem if we are immobilized by the immensity of the task. Further, if we act locally, and do the best we really can to solve this problem, it will disarm the criticism of American hypocrisy. This means cutting down on consumption and making consumption use less resources. This entails the entire battery of things, from recycling to ecologically sound waste disposal, that we read about in environmental journals and books.

The problem will never be solved as long as we believe that God created all the other organisms on earth to serve humans, and that it is our right and even duty to exploit all possible resources. Whatever one's view of what God did or didn't intend, or even whether or not there is a God, ecology and the other environmental sciences have shown over the past century that we are doomed if we really act this way. There are too many intricate links among species in each ecosystem, and many resources, like water and soil, are simply not renewable except over thousands of years. So we have to live in harmony with nature, not as masters of nature.

It is not even clear that the Christian tradition really demands a view of humans as having dominion over nature. As Lynn White has pointed out, the greatest radical in Christian history since Christ was St. Francis of Assisi, and his radical notion was of humility, not only for individual humans but for humans as a species. St. Francis tried to depose humans from their monarchy over all creation and to set up a democracy of all God's creatures. For him, the ant and the cricket are no longer simply a homily for the lazy; they are Brother Ant and Sister Cricket, praising the Creator in their own ways. Later commentators said that St. Francis preached to the birds as a rebuke to men who would not listen, but the records do not really show that. Rather, they show that he preached to the animals because he believed they were God's creatures just as humans are.

The concept of a balance of nature is embedded in Christianity, but in many other religions as well. It goes back at least to the Greeks and the ancient Jews. Many people act as if the balance of nature is something that God created to protect us from our own mistakes. If we do something wrong, the balance of nature will eventually make it right again. But if 20th century science has shown anything, it has shown that nature does not make everything right for us, and that some changes are irreversible. If there is any balance of nature, it is a fragile thing that needs our continued vigilance to protect it. Rather than nature protecting us, we have to protect nature.

Secretary of the Interior, Bruce Babbitt, has been saying since he took office that we have to have much better planning and regulation of the environment to avoid environmental train wrecks like the spotted owl. Once a species is in such bad shape that the Endangered Species Act has to be called into play to save it, the chances are not so good that we will succeed, and in any event, it will be very expensive. So how exactly do we get ahead of the extinction curve?

The idea that is being pioneered by the Nature Conservancy and lately adopted, at least in principle, by federal agencies like the Forest Service, is not to manage single species but to manage entire ecosystems so that they and their component species all remain healthy. I think this idea is on the right track, but a lot of science has to be done before we really know how to manage entire ecosystems. If we are willing to support this research, and then to follow its dictates, the problems probably can be solved. However, it is not obvious we will do so. Research budgets are being cut all over the place, and there are many things that scientists have already discovered that could alleviate the environmental crisis, but these are not being done for political or economic reasons. So ecosystem management is the way to go, but it will just remain a catchy phrase unless we work very hard to make it more than this.


(1)The following writings were used in preparation of this lecture, and they are a good starting point for further reading on the main ideas expressed: Borman, F.H., and S.R. Kellert (eds.), Ecology, Economics Ethics: The Broken Circle (New Haven: Yale University Press, 1991); Ehrenfeld, D.W., Biological Conservation (New York: Holt, Rinehart, and Winston, 1970); Ehrlich, P.R., and A.H. Ehrlich, The Population Explosion (New York: Simon and Schuster, 1990); Ehrlich, P.R., and A.H. Ehrlich, Healing the Planet (New York: Addison Wesley, 1991); Fox, S., The American Conservation Movement: John Muir and His Legacy (Madison, Wisconsin: University of Wisconsin Press, 1986); Groombridge, B. (ed.), Global Biodiversity: Status of the Earth's Living Resources (London: Chapman and Hall, 1992); Simberloff, D., "Species-area relationships, fragmentation, and extinction in tropical forests," pp. 398-413 in S.K. Yap and S.W. Lee (eds.), In Harmony with Nature (Kuala Lumpur: Malayan Nature Society, 1991); Simberloff, D., "The ecology of extinction," Acta Palaeontologica Polonica, 38, 3/4 (1993): 1-15; Western, D., and M. Pearl (eds.), Conservation for the Twenty-first Century (New York: Oxford University Press, 1989); White, L., Jr., "The historical roots of our ecologic crisis," Science, 155 (1967): 1203-1207; Wilson, E.O., The Diversity of Life (Cambridge, Mass.: Harvard University Press, 1992).