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The Preservation of Species
The Value of Biological Diversity
By Bryan G. Norton PRINCETON UNIVERSITY PRESS
Copyright © 1986 Princeton University Press
All rights reserved.
ISBN: 978-0-691-02415-8
CHAPTER 1
Species Leave the Ark One by One
THOMAS E. LOVEJOY
Endangered species are usually perceived as representing no more than a small number of highly individual and esoteric situations — such as the mysterious small tree from the Alatamaha River Valley of Georgia discovered by John and William Bartram in 1765, named in gratitude for Benjamin Franklin, and found only a few times in nature and not since 1803. This perception of disappearing individual species as opposed to a process of biotic impoverishment is a natural one because people identify readily with individual plants and animals, or individual species, even if the organism is only recently familiar to the general public.
In recent years, however, awareness has grown that the problem is actually a matter of considerably greater magnitude than heretofore realized. To a large degree, this is a consequence of the accelerating rates of tropical deforestation.
I. How Many Are There?
Estimates of numbers of endangered species were first restricted to warm-blooded vertebrates, because birds and mammals are among the more noticed elements of the biota. Today, endangered species lists prepared by the U.S. Department of the Interior and by the Species Conservation Monitoring Unit of the International Union for the Conservation of Nature and Natural Resources (IUCN) attempt to encompass all forms of life. This is a very difficult task because most species of plants and animals are still completely unknown to science and there is no information about their status or biology.
Estimates of the magnitude of the problem are usually put in terms of projections (which are not to be equated with predictions) of the number of extinctions that might be expected by the end of the century. These projections assume no major changes in various trends such as population and deforestation. The number of extinctions projected ranges from hundreds of thousands to over a million.
In part because the size of the numbers is startling, there has been some criticism of the figures. Some of the criticism has been justified. In some instances there has been no explanation of how the estimate was obtained. In others, estimates have been made in terms of rates, implying a greater precision than is possible. Further, the meaning of a rate in terms of cumulative numbers has often been ignored. The "one extinction per minute" used by some authors is equivalent to 525,600 extinctions per year (an unlikely or impossible number).
Other criticism has tended to view the large numbers as the outpouring of overwrought biological Cassandras and has asked how they could be so very much greater than historical figures. This criticism ignores basic biology in trying to compare the historical figures for mammalian extinctions with the recent projections which encompass all forms of life. Historical figures for mammalian extinctions are indeed small compared to the projections but they are only meaningful compared to the total number of possible mammalian extinctions (i.e., 4,500, the total number of extant mammal species), or as an indication of accelerating extinction rates.
That there is considerable spread in the estimates is really not surprising, given the difficulties in getting precise information. Just to begin, the size of the biota is only known to an order of magnitude. Estimates of the complete array of life forms on our planet vary from three to ten million, and occasionally go higher. Only about 1.5 million species have actually been described by science and, even then, their full geographic range and ecological peculiarities have not been recorded. In addition to the problem of not knowing how many species there are, what they are, and where they are, there is the additional problem that there exists no accurate estimate of the extent of the major transformations in the biological landscape such as tropical deforestation. Consequently, a considerable variation in estimates can be expected.
What is important is that every effort to estimate extinction rates has produced a large number. This is consistent with what can be observed of human-wrought changes in the biology of the planet. The tropical forests probably hold half or more of all species of plants and animals. Most of the species of primary tropical forests do not occur in second growth as is much more often the case in temperate zones. Nor in most instances are tropical forest plant species able to persist for long periods of time (decades and even centuries) in soil seed banks the way most temperate forest species can. Such characteristics explain why New England's forests have recovered from extensive cutting in the nineteenth century without major loss of diversity, but tropical forests will not do so.
The great numbers of species in tropical forests usually occur at very low densities (few individuals per unit area) and often they are very restricted in distribution. Large numbers of species will almost inevitably be lost from tropical deforestation. The situation is close to the end in the forests of Madagascar where 90 percent of the species are endemic (occur nowhere else), and the Atlantic forest region of Brazil (also high in endemism); the latter is reduced to less than 2 percent of its original extent. Heroic and major last-minute efforts may yet save a good portion of the highly endemic floras and faunas in such areas. Yet nobody expects tropical deforestation to cease tomorrow. The relation between area of tropical forest destroyed and the number of possible extinctions was the basis for the projections in the Global 2000 Report.
Besides the urgency implied by events in the tropics, there is also a growing awareness of the implications of habitat fragmentation for potential extinctions. Habitat fragments have differing ecological dynamics from those they had when once part of continuous wilderness; this change leads the remnant fragments to lose species after isolation. Isolated habitat fragments are almost always subject to this species loss process. Little is known of the process and what forces drive it. Nor is it known how ordered the species loss really is; if there is a predictable order in which species vanish from habitat fragments, those early in the order are much more prone to extinction because they are likely to be lost from every habitat fragment. The process of species loss from fragments of habitats basically calls into question whether many areas set aside to protect particular forms of life, and which are often isolated habitat remnants, will, in fact, actually do so. The activity of civilization has tended to fragment natural landscapes (when not entirely obliterating them), so that the terrestrial portion of the globe has become a biological fretwork each portion of which is going through the process of species loss.
At the same time, people are busy changing the chemistry, if not the physics, of the planet. The recent increase in acid precipitation from burning high-sulfur fuels is a prominent example. The origin of acid rain is not fully understood nor are the effects of this change on environmental chemistry, but there is no question that certain kinds of lakes are vulnerable to biological impoverishment and effects on forests are well known in both Europe and the United States. In the Amazon, excessive deforestation could disrupt the basic hydrological cycle and trigger an irreversible drying trend. That trend in turn could affect the remaining forest and lead to numerous Amazonian extinctions. The increase in atmospheric carbon from burning of fossil fuels as well as from tropical deforestation has serious implications.
Every year a large number of compounds new to nature are produced in laboratories. Some are sufficiently novel that natural systems have not evolved a capacity to cope with and assimilate them. Among the best known and dramatic are the chlorinated hydrocarbons, most notably DDT. These were well on their way to eliminating some species before the problem was recognized and corrected. Great care is taken to test substances destined for human consumption; similar precautions should be taken for substances destined for environmental consumption.
False hope is sometimes derived from noting the few species which have benefited from conversion of our landscape, such as raccoons which have reached nuisance levels in some eastern cities of the United States such as Washington, D.C. It is easy to let such examples suggest the problem cannot be as bad as portrayed. Yet such species are a tiny minority and their success in modified environments makes them what biologists term "weedy" species, i.e., potential pests.
Not only is there a large and unprecedented number of endangered or potentially endangered species, but this also implies an impending net reduction in global biological diversity. While there have been notable episodes of species extinction in the past, during the history of life on earth, overall there has been a net accumulation of species. Extinction has, more often than not, involved a replacement of one species by another, not necessarily closely related to it. Even if the disappearance of much of the Pleistocene megafauna was human-generated, it really only represented a tiny number of extinctions. Consequently, we stand on the brink of an episode of extinctions which is without precedent in the history of humankind.
II. Why Is It Important?
Assuming that the biota contains ten million species, they then represent ten million successful sets of solutions to a series of biological problems, any one of which could be immensely valuable to us in a number of ways. Penicillium mold has the ability to ward off competitive fungi. The French take advantage of this to use goat's milk to produce a cheese (Roquefort) having distinctive flavor and not susceptible to spoilage by other fungi. This same characteristic is used to combat fungal infections of our bodies or those of our domestic animals. This kind of ability was first observed in a Penicillium, which thus provided an impetus for studies of antibiotic activity and resulting medicines. United States superiority in antibiotic medicine was one of many, but nonetheless one of the factors leading to the Allied victory in the Second World War.
Our history is rich in examples of highly useful discoveries based on species previously perceived as worthless. Aspirin, as standard an ingredient of most modern medicine cabinets as any, consists of an organic molecule originally derived from a willow; indeed its chemical name, salicylic acid, is derived from the Latin Salix for willow. The recent discovery of a powerful antiviral substance from a sea squirt is another such example.
Some discoveries have an enormous impact and some minor. There is nothing about abundance (or, therefore, rarity) that correlates with usefulness. If anything, there are arguments that rare species may be more useful on the average than abundant ones. Much is made of the potential and present contribution of wild species. A recent analysis of the United States economy shows that 10 percent of GNP is derived directly from wild resources.
Yet as important as some of the contributions of wild species have been, are, or will be to human society, the greatest contribution is likely to be in the form of knowledge. The pharmaceutical industry is much more likely to attempt to synthesize a new medically useful compound than it is to try to grow the organism in question in large volume, or to harvest it from the wild. This is even more likely with the advent of biological/genetic engineering.
It might seem at first glance that this engineering potential will provide less reason to care about protecting biological diversity; in fact it indicates increased importance. Our knowledge of biological systems is so superficial that there is not a single species for which it can be said with confidence that we know it in its entirety and need not retain it for its potential contribution to biological knowledge. As living organisms we have a vested interest in not limiting the growth of that branch of knowledge known as the science of life. For that reason alone we must be concerned with the survival of each and every species.
The point then is not that the "worth" of an obscure species is that it may someday produce a cure for cancer. The point is that the biota as a whole is continually providing us with new ways to improve our biological lot, and that species that may be unimportant on our current assessment of what may be directly useful may be important tomorrow.
Natural aggregations of species (ecosystems) are more than a large collection of genetic material; they also are involved in ecological processes, often of immediate public service value. A dramatic example is the watershed protection provided by tens of thousands of species in the forests around the Panama Canal. Every time the series of locks is filled and emptied one million gallons of fresh water are used. The canal watershed forests guarantee a steady flow of the fresh water needed for this important link in the world economy.
Many of these processes/services arise from the fundamental fact that living organisms inevitably modify their environment. Indeed the atmospheric composition of this planet is different from all others (high oxygen, for example) because of the presence of life. While it is in one sense paradoxical that life cannot exist without affecting its environment, these modifications have often created conditions favorable to life itself. Life is often also actively involved in maintaining these conditions. For example, the tropical forests of the Amazon are dependent on a minimum amount of rainfall, and yet are (as noted earlier) responsible for generating about half the rainfall in the Amazon basin by hydrological recycling. If the forest were replaced by grassland, rainfall would drop considerably (although not by half since the grasses could return some moisture). The minimum rainfall required for tropical rain forest would then only occur in limited places (e.g., near the Atlantic coast or in places of higher altitude). There, biological factors would not dominate; rather, physical features such as proximity to an oceanic source of moisture or condensation of moisture in rising air masses would generate the necessary rain.
On a global basis the biota is involved in maintenance of the great cycles of water, energy, and the elements. There are already signs that cycles of carbon, nitrogen, and sulfur are being disturbed; disturbance of the biota plays a causal role in most instances, which is augmented in some cases by other factors such as burning of fossil fuels (ironically, fossil biota).
III. Biotic Impoverishment and Economic Impoverishment
The foregoing arguments all carry obvious economic implications. Yet the most worrisome aspect of the endangered species problem comes from a disturbing observation that exists for the most part independently of the foregoing arguments: those nations which are unsuccessful in maintaining their basic diversity of plant and animal life are also the ones least successful in protecting decent standards of living for their people. Notable examples in the Western Hemisphere are El Salvador and Haiti, and the latter is of particular interest in comparison with the Dominican Republic on the other half of the island of Hispaniola.
El Salvador has the highest population density of any non-island nation in the Western Hemisphere. Its original forest cover has been reduced to less than one tenth of its original extent, with an attendant although poorly documented decrease in biological diversity. These population/ natural resource-base problems, exacerbated by a tremendous gap between rich and poor, have led to continuing unrest in El Salvador for decades.
(Continues...)
Excerpted from The Preservation of Species by Bryan G. Norton. Copyright © 1986 Princeton University Press. Excerpted by permission of PRINCETON UNIVERSITY PRESS.
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