BIODIVERSITY

Life on earth began as bacterial cells at least 4,000 million years ago, and it has—with notable, but rare, catastrophic declines in diversity subsequently—expanded, evolved, and complexified across time. In the early-twenty-first century the earth teems with countless species arranged in many diverse patterns and relationships spread across varied landscapes. As human populations have expanded since the industrial revolution, with technologies becoming more powerful and increasingly capable of pervasive impacts, biodiversity is again in decline, this time as a result of human activities, especially the fragmentation of forests and other wild habitats. How to reverse the dangerous trend toward biological simplification has become one of the most urgent global environmental questions.

What Is Biodiversity?

Biodiversity, a contraction of biological and diversity, was introduced as a convenient abbreviation during preparations for a national symposium on the subject in the United States, which was sponsored by the Smithsonian Institution and the National Academy of Sciences (NAS) in 1986. This term, though technically difficult to define, has come to refer to the rich and textured web of life on earth. The term, and the concepts and ideas associated with it, gained world political prominence at the World Conference on Environment and Development in Rio de Janeiro in 1992, where the United Nations Convention on Biodiversity, a document that was subsequently ratified by a majority of nations, was passed. This convention called for the sustainable use and protection of the earth's biological resources, and the term biodiversity has become the rallying point for conservationists and others concerned about the rapid simplification of natural systems in the face of human development.

There are two approaches to defining biodiversity (Wood 1997, 2000). Perhaps the most popular approach is to define it as an inventory of diverse biological items. One such inventory, which has been described as the standard definition of biodiversity, defines it as the sum total of species, genetic variation within species, and diversity of habitats and ecosystems in which species are found (Takacs 1996). Difference definitions, in contrast, define biodiversity as the total of differences among biological entities and processes (Takacs 1996; Wood 1997, 2000). These two approaches differ in that inventory definitions, which simply count elements of different types (species, genes, habitats), tend to count elements of the same type equally in their contribution to total diversity, whereas difference definitions highlight degrees of differentiation. Accordingly, under a difference definition, a species that is the lone member of its genus would be considered to contribute more diversity than a species that shares its genus with others (Solow et al. 1993, Weitzman 1998).

As noted, there are serious technical problems in defining biodiversity. It clearly would be desirable to have a definition that represents biodiversity as a measurable quantity—so that, for example, one could say that a given system is measurably more diverse than another, or that a given system is losing or gaining diversity at a specifiable rate. Unfortunately both inventory and difference definitions fail to provide a measurable index of biodiversity. Decisive arguments show that biodiversity cannot be represented as a list of countable and additive elements. This conclusion follows from the unavoidable fact that living nature can be organized into multiple, but incommensurable, hierarchies. For example, there is a phylogenetic hierarchy of species and genera, among others, as well as a spatial hierarchy of cells, organs, organisms, and ecosystems. Both hierarchies add significantly to the total diversity of life, but the elements of these hierarchies cannot be added together to create a meaningful sum. Similar arguments apply to difference definitions: Biological entities vary across many parameters and aspects, and these cannot be added together to represent a meaningful index of biological diversity (Wood 2000, Sarkar 2005).

This difficulty implies that biodiversity is too complex and multifaceted to be represented by a single measure or to be made a countable quantity, and has led to a search for proxy measures for biodiversity (Sarkar 2005). One popular proxy is simply to use species counts as conventional markers to represent total diversity, which has gained wide acceptance in practice because it is clear and allows relatively unambiguous measures. The consensus view of scientists, however, is that simplified measures such as this cannot capture the full richness and diversity of life. In the United States this simplification was nevertheless embodied in the Endangered Species Act of 1973 (ESA), which has become, despite its narrow focus on endangered species, one of the most important pieces of environmental legislation ever passed by a national legislature. The act concentrates heavily on avoidance of species extinction through a process that lists species as threatened or endangered, limiting damage to the listed species, subspecies, and special populations. Protection of habitat is mainly treated by the act as instrumental to the protection and recovery of endangered and threatened species.

Accordingly it has been suggested that the U.S. strategy—which can be referred to as a rare species paradigm—may be less effective than an alternative strategy developed by Australian practitioners, who develop algorithms that rank possible reserve designs according to their effectiveness, per area set aside, in saving biodiversity (defined in terms of a chosen proxy). The Australian approach, referred to as the declining species paradigm (Caughley 1994), has increasingly been applied in international settings. This approach is to develop and refine an algorithm that ranks various protection strategies according to their efficiency in using space to protect proxy variables chosen to represent managerial goals. This pragmatic approach—which emphasizes shared actions rather than abstract measures—can provide a rough operationalization of biodiversity: Biodiversity is what is saved by the actions of professionals who design reserves that are effective in responding to identifiable forces of simplification that are addressed in a real place (Sarkar 2005).

Speaking more generally, biodiversity can be thought of as the result of a magnificent and eternal process of change, as life has explored countless strategies for survival in countless climates and habitats. These explorations have led to an inexorable increase in diversity across time, because each increment in diversity opens up new possibilities and adaptations for other species, and to the hypothesis that diversity itself causes increases in diversity. This theory also has a negative side: Losses in diversity can increase the likelihood that further losses will occur as species are stressed by loss of mutualist species and populations (Whittaker 1970, Norton 1987). Thus whereas biodiversity has, in the big picture, increased over time, there have also been cataclysmic periods of species loss, and paleontologists speculate that there have been as many as six extinction events in which half or more species disappeared. At least some of these events are associated with meteor strikes on earth and, possibly, as a result of dust from enormous volcanic eruptions. Increasing rates of extinction and endangerment have led some scientists to speculate that the Earth is entering another such event, for the first time as a result of human activities. Whether the human species can survive such an event is not known, but the exponential effects of human activities are impacting the world at a scale previously produced only by global cataclysms.

Fear that the simplification of nature may cause an irreversible spiral of losses inspires scientists and conservationists to advocate strong measures to reverse simplification processes before it is too late. As noted, there exists a broad, practical consensus among experts about what actions are necessary to reverse, or at least slow, such processes such as establishing protected riparian corridors along rivers and developing core reserve areas while managing buffer zones around them. Whether the means, and the will, exists to rein in development that encroaches on wild habitats and drives species toward extinction remains uncertain. Conservationists agree that it is important to save as much biodiversity as possible, though there are seldom adequate resources to do even a fraction of the things that are widely recommended by experts for the protection of sensitive areas and diversity hotspots. Thus whereas success in protecting biodiversity is not assured, broad agreement in strategies to maximize biodiversity does inspire confidence that practitioners know what they are talking about—that the concepts used are clear enough to allow communication and cooperative action—even if no abstract definition of biodiversity can be considered to correspond precisely to any measurable quantity in nature (Norton 2005).

What Is the Value of Biodiversity?

Despite considerable agreement in conservation strategies and protective practices, there remain several crosscutting disagreements regarding why biodiversity protection is important (Norton 1987, 1986). These are: (1) the nature of the value biodiversity has; (2) the units of diversity that should be valued; and (3) the appropriate measures of the value of biodiversity. These disagreements are important because they affect the prioritization given biodiversity protection in competition with other socially valued objectives, and also among various possible conservation objectives.

Disagreements regarding the nature of the value of biodiversity reflect differing theories of value. Monistic theories of value account for all value in nature according to a single measure. Utilitarians, economically oriented and otherwise, advocate decisions based on impacts on human well-being or satisfaction. Other monists have extended ethical concepts, usually applied only to humans, to other species and even to ecosystems, treating elements of nature as ends-in-themselves, as possessing moral considerability, and as having goods-of-their-own that compete with human welfare. The prominence of these two opposed, monistic theories, has resulted in a polarized discussion, often pitting economists against environmental ethicists, and no consensus regarding how to place measurable value on biological diversity has emerged.

The value of biodiversity is better captured by a pluralistic evaluative method, which treats the many social values derived from biodiversity as reinforcing each other. Actions that protect biodiversity protect complex natural systems, reduce soil erosion, promote aesthetic enjoyment and scientific interest, hold open options for economic uses, and support the values of the many individuals who value nature noninstrumentally.

Pluralism, though unpopular within academic disciplines, seems more consistent with the many ways that humans express their dependence upon, and love for, nature. Under a pluralist approach, multiple competing values must be balanced and prioritized against each other, but opportunities also arise to protect multiple social values simultaneously, opening up the possibility of win-win management policies through the protection of natural habitats as homes for biodiversity and many other values. The pluralist approach encourages a more political understanding of the value of biodiversity. Some authors conceptualize the problem of biodiversity protection as one of accepting responsibility for conveying a trust, or a gift from previous to subsequent generations as an obligatory legacy (Weiss 1989, Brown 1994). In a variant on the trust idea, other theorists argue that future generations have rights to a full complement of species and ecosystems, and that these rights should be protected by constitutional constraints that require governments to protect biodiversity (Schlickeisen 1994, Wood 2000). These trust doctrines and the constitutional amendment recommendation, built on a moral concern for the future, complement the idea of sustainable use and development of resources. The goal of protecting the evolved web of life, what scientists call biodiversity—whether for its possible uses in fulfilling human needs, the diverse aesthetic experiences it affords humans, or its noninstrumental value to the fulfillment of human needs—will be one of the great challenges of the future.

BRYAN G. NORTON

SEE ALSO Biophilia;Deforestation and Desertification;Ecology;Environmental Ethics;Rain Forest;United Nations Environmental Program.

BIBLIOGRAPHY

Brown, Peter G. (1994). Restoring the Public Trust: A Fresh Vision for Progressive Government in America. Boston: Beacon Press.

Caughley, Graeme. (1994). "Directions in Conservation Biology." Journal of Animal Ecology 63: 215–244. Outlines the differences between rare species and declining species paradigms.

Norton, Bryan G. (1987). Why Preserve Natural Variety? Princeton, NJ: Princeton University Press. A monograph surveying the science, values, and policies associated with biodiversity.

Norton, Bryan G. (2005). "What Are We Trying to Save? And Why? Toward a Policy-Relevant Definition of Biodiversity." In The Endangered Species Act at 30, ed. J. Michael Scott, Dale Goble, and F. Davis. Washington, DC: Island Press.

Norton, Bryan G., ed. (1986). The Preservation of Species: The Value of Biological Diversity. Princeton, NJ: Princeton University Press. An anthology providing a multidisciplinary review of nature protection.

Sarkar, Sahotra. (2005). Biodiversity and Environmental Philosophy: An Introduction. Cambridge, UK: Cambridge University Press. A highly recommended survey of issues and methods, written from the viewpoint of a philosopher of biology.

Schlickeisen, Rodger. (1994). "Protecting Biodiversity for Future Generations: An Argument for a Constitutional Amendment." Tulane Environmental Law Journal 8: 181–221.

Solow, Andrew; Stephen Polasky; and James Broadus. (1993). "On the Measurement of Biological Diversity." Journal of Environmental Economics and Management 24: 60–68.

Takacs, David. (1996). The Idea of Biodiversity: Philosophies of Paradise. Baltimore: Johns Hopkins University Press. A very useful examination of biologists' ideas on biodiversity.

Weiss, Edith Brown. (1989). In Fairness to Future Generations: International Law, Common Patrimony, and Intergenerational Equity. Tokyo: United Nations University; Dobbs Ferry, NY: Transnational Publishers. An analysis based in the theory of international law, of obligations to the future.

Weitzman, Martin L. (1998). "The Noahs's Ark Problem." Econometrica 66(6): 1279–1298.

Whittaker, Robert H. (1970). Communities and Ecosystems. New York: Macmillan. Whittaker introduced many of the concepts used to discuss biodiversity.

Wood, Paul M. (1997). "Biodiversity As the Source of Biological Resources: A New Look at Biodiversity Values." Environmental Values 6: 251–268. A focused argument for a difference definition, including also a discussion of the value of biodiversity as a source of biological resources.

Wood, Paul M. (2000). Biodiversity and Democracy: Rethinking Society and Nature. Vancouver, British Columbia: UBC Press. An examination of the moral and political obligations associated with protecting biodiversity.