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About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please AREAS OF SCIENTIFIC UNCERTAINTY 179 9 Areas of Scientific Uncertainty The main purpose of the Endangered Species Act is to provide protection for species with an uncertain future, and uncertainty permeates all decisions made under the act. This chapter focuses on the major areas of scientific uncertainty that exist with respect to applications of the ESA. The emphasis is on uncertainties that could be resolved with further research, as opposed to intrinsic uncertainties in species survival. Even in the best of possible worlds, with perfect data and valid estimation and evaluative procedures, there is always a probabilistic element to any assessment of risk. Nonetheless, the committee concludes that none of the scientific uncertainties discussed below is great enough to make the ESA unworkable. ECOSYSTEM-BASED PROTECTION A stated purpose of the ESA is ''to provide a means whereby the ecosystems upon which endangered species and threatened species depend may be conserved . . . ." The means to this end is the listing of individual species. The major threat to most species is loss of habitat, and therefore ecosystem protection is of paramount importance to the overall preservation of species. Because the ESA requires that critical habitat be designated at the time of listing, listing a species has the potential to protect ecosystems and their unlisted components as well. However, this approach can be effective only if habitat protection is pursued rigorously. Less clear is whether listing species, as opposed to a broader based use the print version of this publication as the authoritative version for attribution.

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About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please AREAS OF SCIENTIFIC UNCERTAINTY 180 policy of listing ecosystems, is the best means of achieving this goal. Protecting ecosystems is probably the only way to ensure the long-term survival of large numbers of species, but the best way to achieve such protection is uncertain. Ecosystem Management Species are relatively easy to identify. Ecosystems are difficult to define and certainly more difficult to manage (e.g., see Franklin, 1993; Irwin and Wigley, 1993; Naiman et al., 1993; Wilcove, 1993). For example, a lake ecosystem can be defined by the boundaries of its shoreline or by its shoreline and the terrestrial watershed on which it is critically dependent. Ecosystem protection is a fairly new concept, and policy for implementing it is untested. Nonetheless, it appears to the committee that enough is known to be helpful. Indeed, several federal agencies have expressed their desire to adopt ecosystem-management approaches, and some have developed task- forces to develop those approaches. Definitions of ecosystem management tend to fall into two major categories. The first—some concept of management to achieve various ecosystem goals—is the more difficult to implement. The second category is the idea of keeping other ecosystem components and processes in mind when managing a particular part of an ecosystem. This would mean, for example, that one would keep in mind the needs of marine mammals and birds when harvesting fish; one would keep in mind aquatic ecosystems when managing adjacent uplands (whether for forestry, agriculture, grazing, recreation, development, or any other goal); and one would keep various ecosystem processes and components in mind when managing for protection of endangered species. The second category is already being developed or practiced by many people in federal and state agencies (e.g., LaRoe, 1993; Quigley and McDonald, 1993), and it has the potential to help protect endangered species, to help protect the ecosystems they depend on, and to help reduce social and economic disruption and conflict. Therefore, despite the need for more knowledge, experience, management tools and, in some cases, social acceptance, ecosystem management offers promise. INADEQUATE KNOWLEDGE OF SPECIES AND THEIR ROLES IN ECOSYSTEMS The Endangered Species Act has been applied almost exclusively to vertebrates, invertebrates, and vascular plants. For small or inconspicuous organisms, a large fraction of the biota probably has not been classified. Furthermore, new species even of conspicuous taxa are still being discov use the print version of this publication as the authoritative version for attribution.

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About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please AREAS OF SCIENTIFIC UNCERTAINTY 182 wardly, biased estimates of the risk of extinction are preferred, so that errors in risk assessment would tend to be on the side of species. Intrinsic Limits of Extinction Models Biological models that jointly incorporate demographic and environmental (spatial and temporal) variation, age structure, and genetics can be analyzed by computer simulation. However, predictions emanating from these models will always be subject to uncertainty. Most notably, some aspects of the structure of the model (e.g., mode of density dependence, temporal and spatial patterns of environmental variation, and frequency and magnitude of catastrophes) will almost always be in doubt. Even for rare cases in which the essential information is available, its relevance to predictive models can be limited. For example, fundamental features of population structure and dynamics of a species in jeopardy because of environmental change might be altered in unanticipated ways. To a certain extent, those types of uncertainty can be dealt with by using a model structure and conservative enough parameter estimates that the predicted risk of extinction will most likely be an overestimate. In addition, evaluation of the sensitivity of a model's predictions to variation in its parameters can be used to identify the features of a population for which accurate estimates are most critical to the decision process. These sensitivity analyses should be conducted routinely, and the results should be used to direct future research. LACK OF BASIC INFORMATION Whether explicitly or implicitly, all decisions concerning rare, threatened, or endangered species are based on assessments that have at least some quantitative basis, even if that basis is not explicit. Yet, critical data to make informed decisions on proposals for listing, to designate critical habitat, and to develop recovery and management plans are usually lacking. Our biological understanding of many rare, threatened, or endangered species does not extend far beyond a taxonomic description and a coarse geographic distribution. That lack of data should not be the basis for failure to list a species if other information is available to indicate that listing is otherwise warranted. The act calls for the use of the best scientific data available in the decision-making process. It does not, and should not, require that all desirable data be available at the time of listing. Dynamics of Natural Populations Recovery plans often set goals based on target population sizes. Equally use the print version of this publication as the authoritative version for attribution.

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About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please AREAS OF SCIENTIFIC UNCERTAINTY 183 important is the need to stabilize the mean population density. One of the largest gaps in our knowledge of the population biology of most species concerns the natural temporal and spatial variation that exists in key demographic factors. That information is critical to evaluating the risk of extinction, regardless of the mean population size. Systematics Protection of ecosystems is becoming recognized as an attractive option for conserving biological diversity. However, ecosystems are composed of species and populations, and those components of ecosystem structure must be understood. Yet the vast majority of species in the United States are unknown and unnamed. Even for many of the named species, virtually nothing is known of their geographic ranges, population structure, demography, ecology, or practically any aspect of their biology. We have only the roughest of estimates of how many species of organisms reside in this country. A recent NRC report on the National Biological Survey (now the National Biological Service) (NRC, 1993a) recommended a commitment to a detailed study of a significant portion of our biota. Although some of the more visible vertebrate groups, such as birds and mammals, are well known, many plant groups and most invertebrates, except for some commercially important ones, remain virtually unstudied. Some large ecologically important groups have few or no systematists studying them. Any realistic attempt to provide even a basic inventory of our biota will need significant new resources for training and supporting systematic biologists. Wise understanding, management, and conservation of our biota need a much better picture of what organisms inhabit our country. Do Minimum Viable Population Sizes Exist? A popular heuristic concept in conservation biology is that of a minimum viable population size (MVP), i.e., a threshold population size below which rapid extinction is virtually guaranteed. Should MVPs exist in reality, numerical guides to them would be useful as listing criteria. At this point, there is little compelling evidence that general guidelines can be made in this regard. Certainly, small populations are more vulnerable to extinction than large ones, but it remains to be seen whether there is some critical population size below which the vulnerability to extinction increases suddenly. It is perhaps more useful to estimate extinction probabilities as a function of time for different population sizes than to identify some specific MVP, as discussed in Chapter 7. use the print version of this publication as the authoritative version for attribution.

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About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please AREAS OF SCIENTIFIC UNCERTAINTY 184 THE PROTECTION OF GENETIC DIVERSITY In previous chapters, we described the importance for the survival of species of maintaining genetic diversity for adaptive characters within and between populations. All species are now, and perhaps always have been, confronted with a globally changing environment. Many rare species have the additional burden of being confined to habitats that are changing rapidly in response to local human activity. Although all species have evolved behavioral and physiological mechanisms for coping with environmental change, the range of environments within which such homeostatic mechanisms are operative is normally confined to the conditions experienced over long periods. For species encountering entirely new environmental conditions, evolutionary flexibility is essential for long-term survival. Thus, the preservation of diversity at the species level is intrinsically dependent on the maintenance of genetic diversity within species. The difficulty lies in the identification and quantification of this genetic diversity. Uncertainty Regarding Future Adaptive Challenges to Species If information on all quantitative-trait variation could be obtained for an endangered species, it would still be difficult to identify which characters should be evaluated, because we would be unsure of the selective challenges that would confront species in the future or the characters that will contribute to adaptive change. With this uncertainty, the best strategy for the maintenance of genetic diversity within species is the implementation of protection programs that are likely to maximize genetic variation for all characters. Programs designed to maximize effective population size will naturally maximize the expected amount of genetic variation as well. Because individual genomes are mutable, populations that are devoid of useful quantitative-genetic variation can replenish that variation over tens of generations and should not be ruled out as viable evolutionary lineages. FEASIBLE MANAGEMENT STRATEGIES Perhaps the paramount challenge to future managers of endangered species concerns the degree to which management and recovery plans can be developed within a framework that incorporates a range of continuing human activities. Numerous issues remain unresolved, such as the design of reserves, reconstruction of habitat, the usefulness of captive breeding and supplementation programs, and the effects of environmental change. use the print version of this publication as the authoritative version for attribution.

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About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please AREAS OF SCIENTIFIC UNCERTAINTY 185 The Spatial Structure of Reserves A major challenge for conservation biology is the need to develop methods for ascertaining optimal strategies for moving species toward recovery goals when resources and critical habitat are in limited supply, as they always are. The spatial arrangement of habitats can have substantial effects on the persistence of metapopulations, but our understanding of even the most basic issues is still undeveloped (NRC, 1993b). Analogous to the concept of minimum viable population size, there might be a threshold number of subpopulations or a threshold degree of isolation beyond which a metapopulation becomes highly vulnerable to extinction, although this would certainly be expected to vary from species to species, depending on their biological features. Corridors and Edge Effects In principle, corridors between local demes can allow metapopulations of the demes to serve as buffers from extinction in a stochastically varying environment. However, because of their large edge effects, corridors often contain inhospitable habitat through which migration is risky. Consequently, corridors can be sinks as well as sources of individuals in a metapopulation context. Attempts to evaluate whether management of a species should involve a few very large reserves versus many smaller ones will be shortsighted if they do not take into account the demographic consequences of corridors (NRC, 1993b). Fragmentation of habitat, in general, is a particularly serious area of uncertainty. Because ecosystem structure develops over several hundreds to thousands of years, several human generations could pass before the full consequences of habitat fragmentation and the resulting edge effects were revealed. Reconstruction of Habitat In habitat conservation plans involving mitigation, proposals by developers to reconstitute ecosystems at alternative sites are becoming increasingly common. Careful management of species whose biology is well understood can lead to their protection in altered environments. However, development of complex communities for listed species must be approached cautiously, because we often are dealing in theory rather than proven ability. Reconstituted ecosystems can have very different internal and external interactions than their predecessors (NRC, 1992). As a consequence, maintenance of such ecosystems might require long-term and, perhaps at times, intensive management. Ecosystems, like species, evolve over time and use the print version of this publication as the authoritative version for attribution.

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About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please AREAS OF SCIENTIFIC UNCERTAINTY 186 space as their component species wax and wane. Artificial manipulation (management) might therefore be necessary if we are to focus on a particular listed species or species set as a target for management. Consequences of Captive Breeding and Supplementation From a genetic perspective, a fundamental issue for which we have almost no empirical information is the degree to which semi-isolated populations develop genomic incompatibilities, which upon crossing, would be exhibited as reduced fitness of the offspring. This issue is becoming increasingly important as recovery plans incorporate captive breeding, supplementation, and sometimes, hybridization procedures into management policies. Global Environmental Change In applications of the ESA, the major focus on species protection has been on local issues, such as dam and road building, logging and mining, grazing, and housing development. However, evidence suggests that human activity is causing global changes in temperature and the chemical composition of the atmosphere (Abrahamson, 1989; Kareiva et al., 1993). Even before humans had the capacity to cause environmental changes at larger than local scales, regional and global environments were changing; indeed they have changed as long as life has been on earth (see Chapter 2). Those types of changes, particularly when combined with habitat fragmentation, could pose major threats to rare and sensitive species. Policies for managing biodiversity will be short-sighted if they are developed in a setting that does not consider the implications of global environmental change. VALUING RARITY Many uncertainties in economics (defined broadly as the science of human choice and valuation) relate to the Endangered Species Act. One of the largest of these concerns the valuation of rarity. Valuation is an enormously controversial topic. Some cognitive psychologists argue that strong environmental values are not represented in monetary form in people's mental models (e.g., Gregory et al., 1993). Tversky et al. (1988) argued that the way people rank and order items depends on the measure used. Applied to the case of endangered species, it means that people might put a higher dollar value on one species than another but reverse the ordering if asked to decide which species should be preserved to make the greatest contribution to genetic diversity. Many issues are contentious between the fields of economics and ecology. Indeed, some econo use the print version of this publication as the authoritative version for attribution.

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About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please AREAS OF SCIENTIFIC UNCERTAINTY 187 mists and philosophers have doubted the ability of economics to solve this question because of the diversity of attributes being evaluated, the lack of information available, and especially the difficulty of including moral and long-term considerations in the valuation (e.g., Norton, 1988; Norgaard, 1988). Others have pointed out the usefulness of having some sort of balanced and complete economic analysis, even if it includes only short-term considerations (e.g., Randall, 1988). This discussion is limited to the economic perspective. Value does not inhere in objects. The attribution of values to objects by individuals is motivated by cultural and religious underpinnings, but our tastes and preferences are also influenced by more transitory forces of television, advertising, and the print media. Therefore, explaining taste is presently very much an exploratory enterprise. Rare things often are valued because ownership is a conspicuous way of displaying superiority. So some are willing to pay a great deal to possess a private good that few others can afford to have. Unfortunately, no research has established the relationship between rarity and dollar value. But rarity and great value are not the monopoly of private goods. Many feel great exaltation in front of Michelangelo's Pietà; looking at one of Christo's wraps; or observing natural wonders, such as the great migrations of zebras, wildebeests, and other animals between Kenya and Tanzania, or tens of thousands of migratory birds taking flight from a lake. The economic analog of these ideas is a willingness to pay if necessary to enjoy these experiences rather than go without one or more of them. Great economic value can arise from great quantity and is not limited to things quantitatively scarce, as long as qualitative attributes are acknowledged. Goods and services have high economic value when they are economically scarce, i.e., when the demand for them is large relative to supply. A key element in explaining whether consumers place a high or low value on something is the availability of substitutes. The destruction of something we like enormously is not so bad if we can easily find a substitute. Few substitutes is a necessary but not sufficient condition for high value. (For example, rare fatal diseases are not particularly valuable.) Not all rare things are valuable. Endangered species are, by definition, rare (or nearly so), but quantitative rareness is not a sufficient attribute to conclude that any and all endangered species have great economic value. Wilson (1988) and others effectively have heightened public awareness of the accelerated pace of species extinction—in recent years, three per hour in the rain forests alone, according to Wilson's latest estimate (Wilson, 1992). Yet we are complacent with that knowledge and with knowledge of threats to tropical rain forests and other hotspot ecosystems around the world. In the final analysis, allocated funds reveal how valuable the citizenry thinks endangered species are and use the print version of this publication as the authoritative version for attribution.

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About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please AREAS OF SCIENTIFIC UNCERTAINTY 188 how much it is willing to give up other things to have greater preservation activities. Congress annually appropriates funds for the Office of Endangered Species in the United States that are not adequate to list more than a small fraction of the candidate species or to pay for more than a fraction of the possible recovery plans for all endangered species. U.S. voters and their representatives in state and national legislatures have yet to demonstrate enthusiasm in support (or willingness to make sacrifices for) of species preservation despite the belief of many scholars and researchers that the pace of extinction is too rapid. Preservation efforts might be facilitated if estimates of economic value of rare and endangered species were available. Estimates of value are elusive because of the nature of the benefits (Brown, 1990); with few exceptions, credible estimates do not exist. Many suggest that a species is worth preserving if it yields products of commercial worth. It is easy to find specific plants with great commercial value, such as the rosy periwinkle (Catharanthus roseus ) which has been used in a cure for acute lymphocytic leukemia and Hodgkin's disease. But generalization of an estimate of economic value to all species is more problematical, particularly since the chance of finding a product of economic value is so small, perhaps on the order of 1 in 10,000 (Aylward et al., 1993). And preservation is costly and requires tradeoffs. It is not surprising that companies are reluctant to make privileged information about specific costs and revenues public, so data do not exist to estimate the commercial economic value of genetic resources in general and any species in particular. Preserving for commercial value is not a good strategy, unless endangered species can be ranked according to the chance of successful discovery of commercial products and expected value if successful. Even if the expected economic return could be accurately predicted, estimating the commercial value of species correctly will result in a systematic underestimate of species' value to society. If the species are common property, owned by none, then others can use them directly or indirectly for competitive commercial gain, so that value of any template or product developed from a species is devalued by the first discoverer who knows that a successful rival cannot be far behind. Patents are an imperfect protection. Removing common property status is tantamount to privatization, in which case the private "owners," apart from exceptional cases, act as monopolists and exploit their monopoly power to the detriment of social welfare. Many species are valuable because they provide either food or recreation directly to the consumer. However, this direct consumptive value is an excluded source of value for rare species. The benefits we derive from species as goods—either commercial or consumptive—are relatively easy to value compared with another type of value that derives from the services that species perform within the ecosystems that contain them. Such ser use the print version of this publication as the authoritative version for attribution.

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About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please AREAS OF SCIENTIFIC UNCERTAINTY 189 vices include the maintenance of fertile soil and water, control over the composition of the atmosphere, and regulation of the climate and the hydrological cycle (including flood control), and pest control. These major benefits to the human economy and to human well-being are called ecosystem services by ecologists, but that phrase masks the important roles that individual species or groups of species play in providing those services. For example, some species of microorganisms (denitrifying bacteria) convert nitrate in soil into a gas, nitrous oxide, that plays an important role in regulating the concentration of atmospheric ozone. Difficulty in valuing the roles of individual species in providing these services arise from uncertainty over the actual economic value of fertile soil, clean water, and other ecosystem-derived benefits. Indeed, Norton (1988) equated that value to ''the summed value of all the GNPs of all countries from now until the end of the world." Another part of a species' value is called non-use value. We can derive value from species by knowing they exist today—for example, the value of viewing and photographing them. An illustrative study of these values for elk, bighorn sheep, and grizzly bear was reported by Schulze et al. (1981). Many studies document that a substantial fraction of species values arises if we can be assured that they will be around in the future for subsequent generations to enjoy. The literature on the estimation of the non-use value of species is very modest. All studies estimating non- use value use a contingent valuation method, discussed below. The value of preserving the whooping crane population at the Arkansas National Wildlife Refuge in Texas for viewers and non-viewers has been estimated by Stoll and Johnson (1984) and Bowker and Stoll (1988). Hageman (1985) valued blue whales, bottlenose dolphins, California sea otters and northern elephant seals. Brown and Henry (1989) estimated the value of preserving elephants in Kenya. Boyle and Bishop (1987) estimated the value of preserving the striped shiner, a Wisconsin endangered species. Boyle and Bishop (1986) also have estimated the existence value of eagles by focusing, in part, on whether respondents view eagles or not. Brown et al. (1994) estimated the value of the northern spotted owl, as have Hagen et al. (1991). The valuation of non-use by economists is new and controversial. By its very nature, such valuation is not founded on behavioral observations, which is the source of controversy. Non-use values cannot be observed from organized markets. The research method is contingent valuation (Cummings et al., 1986; Mitchell and Carson, 1988). It involves the design of a survey that elicits dollar values that, for example, represent a respondent's willingness to pay for the preservation of one or more rare species. Critics argue that the values estimated from contingent value surveys are hypothetical and lack credibility. Advocates rebut that socioeconomic factors consid use the print version of this publication as the authoritative version for attribution.

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About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please AREAS OF SCIENTIFIC UNCERTAINTY 190 ered to be determinants of value have the right sign (i.e., they are positive when expected to be and negative when expected to be) and are statistically significant in well-designed studies and that more than 1,000 contingent valuation studies have been done in more than 40 countries. Controversy over the method of contingent valuation was sparked by the Exxon Valdez oil spill, because the regulations call for such studies. The National Oceanic and Atmospheric Administration, a federal trustee for natural resources injured by oil spills, created a panel composed of Nobel Prize winners in economics and other experts. The panel approved of the contingent valuation method, providing certain criteria were met (NOAA Panel on Contingent Evaluation, 1993). The case on economic grounds for preserving endangered species depends crucially on the magnitude of non-use values for species. Although we may believe that any or all endangered species are too valuable to sacrifice, there is an inadequate scientific basis to demonstrate whether citizens are willing to make the sacrifices necessary to save all endangered species in this country now and in the foreseeable future. In addition, economic analyses are less effective when assessing long-term values than short-term ones. The expected short-term use value in monetary terms of preserving many of the tens of millions of extant species is likely to be small relative to the short-term real costs of saving them (Brown, 1990; Gregory et al., 1993), especially if externalities such as ecosystem goods and services are not factored into the analysis. In part because of uncertainties in biological knowledge, the long-term costs and benefits of protecting endangered species and their ecosystems is poorly known. In our world of limited resources, the harsh fact is that we must give to get. In the absence of scientific facts, belief, not science, defends the view that endangered species are more economically valuable to citizens of the United States than the value of resources it will take to save them. However, many policy decisions concerning public goods are made without compelling economic arguments. It has also been argued that economic and ecological values are consistent with each other and that this consistency should be recognized by policy makers (e.g., Ashworth, 1995), so inasmuch as preserving species is related to preserving ecosystem functioning, preserving species should lead to an enhancement of both ecological and economic values. REFERENCES Abrahamson, D.E. 1989. The Challenge of Global Warming. Washington, D.C.: Island Press. Ashworth, W. 1995. The Economy of Nature: Rethinking the Connections Between Ecology and Economics. New York: Houghton-Mifflin. Aylward, B.A., J. Echerria, L. Fendt, and E. Barbier. 1993. The Economic Value of Species use the print version of this publication as the authoritative version for attribution.

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About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please AREAS OF SCIENTIFIC UNCERTAINTY 191 Information and Its Role in Biodiversity Conservation: Case Studies of Costa Rica's National Biodiversity Institute and Pharmaceutical Prospective. London Environmental Economics Centre, London, U.K. Begon, M., J.L. Harper, and C.R. Townsend. 1986. Ecology: Individuals, Populations, and Communities. Sunderland, Mass.: Sinauer Associates. Bowker, J.M., and J.R. Stoll. 1988. Use of dichotomous choice nonmarket methods to value the whooping crane resource. Am. J. Agr. Econ. 70 (2):372-381. Boyle, K.J., and R.C. Bishop. 1986. The economic valuation of endangered species of wildlife. Trans. North Am. Wildl. Nat. Resour. Conf. 51. p. 153-161. Boyle, K.H., and R.C. Bishop. 1987. Toward total valuation of Great Lakes fishery resources. Wat. Resour. Res. 5:943-950. Brown, G.M., Jr. 1990. Valuation of genetic resources. Pp. 203-229 in The Preservation and Valuation of Biological Resources, G.H. Orians, G.M. Brown, Jr., W.E. Kunin, and J.E. Swierbinski, eds. Seattle, Wash.: University of Washington Press. Brown, G.M., Jr., and W. Henry. 1989. The Economic Value of Elephants. International Institute for Environment and Development. LEEC Paper 89-12. London Environmental Economics Centre, London, U.K. Brown, G.M., Jr., D. Layton, and J. Lazo. 1994. Valuing Habitat and Endangered Species. Institute for Economic Research, University of Washington, Seattle, Wash. Cummings, R.G., D.S. Brookshire, and W.D. Schulze, eds. 1986. Valuing Environmental Goods: An Assessment of the Contingent Valuation Method. Totowa, N.J.: Rowman and Allanheld. Franklin, J.F. 1993. Preserving biodiversity: Species, ecosystems, or landscapes? Ecol. Appl. 3:202-205. Gregory, R., S. Lichtenstein, and P. Slovic. 1993. Valuing environmental resources: A constructive approach. J. Risk Uncertainty 7:177-197. Hageman, R. 1985. Valuing Marine Mammal Populations: Benefit Valuations in a Multi-Species Ecosystem. Admin. Rep. J-85-22. National Marine Fisheries Service, Southwest Fisheries Center, La Jolla, Calif. Hagen, D., J. Vincent, and P. Welle. 1991. Benefits of Preserving Old-Growth Forests and the Northern Spotted Owl. Working paper prepared at Western Washington University, Bellingham, Wash. Irwin, L.L., and T.B. Wigley. 1993. Toward an experimental basis for protecting forest wildlife. Ecol. Appl. 3:213-217. Kareiva, P.M., J.G. Kingsolver, and R.B. Huey, eds. 1993. Biotic Interactions and Global Change. Sunderland, Mass.: Sinauer Associates. LaRoe, E.T., III. 1993. Implementation of an ecosystem approach to endangered species conservation. Endangered Species Update 10 (3&4):3-6. Mitchell, R.C., and R.T. Carson. 1988. Fusing Surveys to Value Public Goods: The Contingent Valuation Method. Resources for the Future, Washington, D.C. Naiman, R.J., H. Décamps, and M. Pollock. 1993. The role of riparian corridors in maintaining regional biodiversity. Ecol. Appl. 3:209-212. NOAA (U.S. National Oceanic and Atmospheric Administration) Panel on Contingent Evaluation. 1993. Fed. Reg. 58(10):4602-4614. Norgaard, R.B. 1988. The rise of the global exchange economy and the loss of biological diversity. Pp. 206-211 in Biodiversity, E.O. Wilson, ed. Washington, D.C.: National Academy Press. Norton, B. 1988. Commodity, amenity, and morality: The limits of quantification in biodiversity. Pp. 200-205 in Biodiversity, E.O. Wilson, ed. Washington, D.C.: National Academy Press. use the print version of this publication as the authoritative version for attribution.

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About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please AREAS OF SCIENTIFIC UNCERTAINTY 192 NRC (National Research Council). 1992. Restoration of Aquatic Ecosystems: Science, Technology, and Public Policy. Washington, D.C.: National Academy Press. NRC (National Research Council). 1993a. A Biological Survey for the Nation. Washington, D.C.: National Academy Press. NRC (National Research Council). 1993b. Setting Priorities for Land Conservation. Washington, D.C.: National Academy Press. Quigley, T.M., and S.E. McDonald. 1993. Ecosystem management in the Forest Service: Linkage to endangered species management. Endangered Species Update 10 (3&4):30-33. Randall, A. 1988. What mainstream economists have to say about the value of biodiversity. Pp. 217-223 in Biodiversity, E.O. Wilson, ed. Washington, D.C.: National Academy Press. Schulze, W.D., R.C. d'Arge, and D.S. Brookshire. 1981. Valuing environmental commodities: Some recent experiments. Land Econ. 57 (2):151-172. Stoll, J.R., and L.A. Johnson. 1984. Concepts of value, nonmarket valuation, and the case of the whooping crane. Trans. North Am. Wildl. Nat. Resour. Conf. 49:382-303. Tversky, A., S. Sattah, and P. Slovic. 1988. Contingent weighting in judgement and choice. Psychol. Rev. 95:371-384. Wilcove, D. 1993. Getting ahead of the extinction curve. Ecol. Appl. 3:218-220. Wilson, E.O., ed. 1988. Biodiversity. Washington, D.C.: National Academy Press. Wilson, E.O. 1992. The Diversity of Life. Cambridge, Mass.: Harvard University Press. use the print version of this publication as the authoritative version for attribution.