WASHINGTON -- Changes are needed in the way biological populations and habitat are designated for protection under the Endangered Species Act, concludes a report released today by a committee of the National Research Council. The committee's study was prepared in response to a bipartisan request from leaders of the previous Congress for an independent evaluation of the Act's scientific basis.

"Since 1973, when the Endangered Species Act was passed, scientific knowledge has been anything but static," said committee chair Michael T. Clegg, professor of genetics and dean of the College of Natural and Agricultural Sciences at the University of California, Riverside. "In general, there has been a good match between science and the Act. But in places where this agreement is poorer, we recommend changes to improve its effectiveness."

The 1973 Endangered Species Act and its amendments constitute the broadest and most powerful law to protect endangered species and their habitats. It has stringent requirements that mandate public and private parties to avoid harming endangered and threatened species and prohibit federal agencies from damaging "critical" habitats essential for species survival.

Species extinctions have occurred since life has been on Earth, but the current rate of extinction is among the highest in the entire fossil record. The introduction of non-native species and especially the degradation and loss of habitat are causing extinctions at a rate that many scientists consider a crisis.

The ultimate goal of the Endangered Species Act is to ensure the long-term survival of a species, but the recovery plans designed to achieve this goal often are developed too slowly or have provisions that cannot be justified scientifically, the committee concluded. To ensure that recovery plans are effective, the U.S. Fish and Wildlife Service, which oversees each plan, should establish explicit guidelines for developing those plans. Species recovery plans should include as much guidance as possible concerning which human activities are likely to harm recovery and which are not, to enable people to plan economic activities. Also, for purposes of evaluation, plans should incorporate estimates of the probabilities of achieving various recovery goals over different periods of time.

HABITAT PROTECTION

The relationship between vanishing habitats and vanishing species nationwide is well documented, the committee said. Consequently, protecting species in the wild most often means conserving habitats. The Act's emphasis on protecting habitat reflects current scientific understanding of this crucial relationship.

But detailed information needed to designate critical habitat for a given species often is lacking. Just because a species occurs within a habitat does not necessarily mean that it requires that habitat, nor does it mean that the present amount and quality of habitat is critical to species survival, the committee noted. To complicate matters, the absence of a species from a given habitat does not mean that the habitat is not critical to the survival of the species. These uncertainties, combined with public concern over economic consequences, often make designating critical habitat both controversial and arduous, thus delaying or preventing protection.

To avoid such situations, the committee recommended that when a species is listed as endangered, a core amount of "survival habitat" should be protected -- without reference to economic impact -- as an emergency, stop-gap measure. This survival habitat should be able to support either current populations or the population necessary to ensure short-term survival for a period of 25 to 50 years, whichever is greater. When the required recovery plans are adopted or the required critical habitat is identified and designated, the survival-habitat protections should automatically expire.

There is no biological or physical reason that standards relating to habitat protection, species survival, and recovery should differ for public and private lands, the committee said. The degree to which public and private entities should bear the responsibilities of the Endangered Species Act is a policy decision, not a scientific matter. But there is no escaping the scientific conclusion that all species have certain biological and physical requirements no matter who owns the habitats, and that public and private landowners do not always respond in the same way to laws, regulations, and other incentives. As a result, regulations applied equally on public and private lands might not provide the same degree of species protection, although the scientific criteria on which the regulations are based are the same. For this reason, different management policies may be required for public and private lands.

The committee endorsed regionally based, negotiated approaches to the development of habitat conservation plans needed to protect endangered and threatened species and their habitats. The U.S. Fish and Wildlife Service should provide guidance on obtaining the necessary biological data and other information for the development of these plans, the committee said.

Conflicts between what is needed to protect different species in the same geographical region will become increasingly common, though such conflicts have been rare in the past, the committee said. The most effective way to avoid conflicts is to maintain protected areas large enough to allow for the existence of a diverse array of habitats.

THE SPECIES CONCEPT

The question of what constitutes a species under the Endangered Species Act can be difficult, requiring scientific interpretations about the subtle physical, genetic, or behavioral characteristics that distinguish subgroups within a species from one another, the committee said. The Act's inclusion of these distinct population segments is scientifically sound and should be retained.

To provide greater scientific objectivity in identifying these population segments, the report recommends using the concept of "evolutionary units" to identify groups within subspecies with distinctive behavioral and genetic characteristics. By focusing attention on the important attributes of organisms, the use of evolutionary units would provide policy-makers with an additional scientific basis for determining which groups of plants and animals merit protection. This is not likely, however, to result in a major change in the number of organisms recognized as eligible for protection under conservation laws, the committee said.

Identification of evolutionary units should be made independently from deciding whether they need protection, the committee said. Although there may be persuasive reasons unrelated to science to protect certain plants and animals distinguished by political jurisdiction alone, there might not be scientific reasons for listing them as evolutionary units. For example, bald eagles in the contiguous 48 United States and in Canada intermix and are not biologically distinct, so there is no scientific justification for identifying the U.S. population as an evolutionary unit. Similarly, protection status of the American alligator and the American brown bear have been based more on management, aesthetic, and political considerations than on scientific grounds.

ADDITIONAL PROTECTIONS

More approaches need to be developed and implemented as complements to the Act to prevent the continued, accelerating loss of species and to reduce economic and social disruption and uncertainty, the committee said. The Endangered Species Act by itself cannot prevent the loss of species and their habitats but should be viewed as only one part of a comprehensive set of tools for protecting them.

Many federal, state, and local governments and private organizations are developing such approaches, including cooperative management (shared decision-making among several government and non-government groups); the management of ecosystems and landscapes; the reconstruction or rehabilitation of damaged ecosystems; the development of mixed-use areas that provide for human activities as well as wildlife habitat; and the use of various market-based economic incentives.

The National Research Council is the principal operating agency of the National Academy of Sciences and the National Academy of Engineering. It is a private, non-profit institution that provides science and technology advice under a congressional charter.

Funding for the study was provided by the U.S. Fish and Wildlife Service of the Department of the Interior. A committee roster is overleaf.

*Pre-publication copies of the report, Science and the Endangered Species Act, are available from the National Academy Press at the mailing address in the letterhead; tel. (202) 334-3313 or 1-800-624-6242. The cost of the report is $45.00 (prepaid) plus shipping charges of $4.00 for the first copy and $.50 for each additional copy. Reporters may obtain copies from the Office of News and Public Information at the letterhead address (contacts listed above).

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Date: May 24, 1995
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In addition to the Section 7 prohibition of any federal action that jeopardizes an endangered species or its critical habitat, Section 9 prohibits the taking of an endangered species of fish or wildlife(or, by regulation, of threatened species). Sections 7 and 9 are major sources of the act's power as well as numerous controversies. In particular, the prohibition against taking endangered species has raised questions among private landowners: taking is fairly broadly defined in the ESA and even more broadly in some regulations. How broad the definition of taking in regulations should be is currently undergoing review by the U.S. Supreme Court. The court's decision will be important in determining the future of some of the controversies about the taking prohibition. (Editor's note: Babbitt v. Sweet Home Chapter of Communities for a Great Oregon ruling issued June 29, 1995. )

As human activities continue to affect species populations and their habitats, two major questions arise concerning the ESA. First, the focus of this report: is the ESA soundly based in science as an effective method of protecting endangered species and their habitats? The second question--of great public importance, but not part of this committee's charge--concerns the desired public policy with respect to protecting endangered species and their habitats, i.e., what are the costs and benefits, and to what extent is the public willing to incur the costs?

THE PRESENT STUDY

In November of 1991, Senator Mark Hatfield, Representative Thomas Foley, and Representative Gerry Studds wrote to the chairman of the National Research Council requesting a study of "several issues related to the Endangered Species Act." The request focused on scientific matters related to the act. After receiving funding from the U.S. Fish and Wildlife Service in September 1992, the NRC's Board on Environmental Studies and Toxicology convened the Committee on Scientific Issues in the Endangered Species Act. The committee's membership includes expertise in ecology; systematics; population genetics; wildlife management; risk and decision analysis; the legal, legislative, and administrative history of the Endangered Species Act; economics; and the implementation of the ESA from public and private perspectives. The committee's statement of task is based very closely on the letter of request from the three members of Congress (see Appendix A).

The committee was asked to review the following issues and to evaluate how they relate to the overall purposes of the Endangered Species Act:

• Definition of species. The committee was asked to review how the term species has been used to implement the ESA, and what units would best serve the purposes of the act.
• Conservation conflicts between species. The committee was asked how frequent or severe conflicting conservation needs are when more than one species in a geographic area are listed as endangered or threatened under the ESA, and to make recommendations to resolve these conflicts.
• Role of habitat conservation. The committee was asked to evaluate the role of habitat protection in the conservation of species and to review the relationship between habitat-protection and other requirements of the act.
• Recovery planning. The committee was asked to review the role of recovery planning under the act and to consider how recovery planning could better contribute to the purposes of the act.
• Risk. The committee was asked to review the role of risk in decisions made under the ESA (such as what constitutes sufficient "endangerment" to require listing of a species, what constitutes jeopardy, adverse modifications, reasonable and prudent alternatives, taking, conservation, and recovery). It was also asked to review whether different degrees of risk ought to apply to different types of decisions (e.g., should an endangered species be at greater risk than a threatened species to justify listing?) and to identify practical methods for assessing risk to achieve the purposes of the act better while providing flexibility in appropriate circumstances to accommodate other objectives as well.
• Issues of timing. The committee was asked to review the timing of key decisions under the ESA and to consider ways of improving such timing under the act to serve its purposes better while minimizing unintended consequences.

The committee held meetings in Washington, D.C., and Irvine, California, where it received briefings from federal officials, congressional staff, Senator Mark Hatfield, Secretary of the Interior Bruce Babbitt, members of private conservation organizations and of private industry, and other experts. It has also made use of many sources of information, including previous NRC reports; documents and studies done by other agencies; and relevant published literature from scientific journals, symposia, and books.

This report reviews scientific issues related to the ESA. The overall conclusion is that the ESA is based on sound scientific principles. Many scientific advances have been made since the ESA was passed in 1973, and they provide opportunities to improve the act's implementation, especially with respect to identifying species, subspecies, and distinct population segments, with respect to estimating risks of extinction, and economic and decision analyses. Although it is difficult to quantify the effectiveness of the act in preventing species extinction, there is no doubt that it has prevented the extinction of some species and slowed the declines of others. It is equally clear that the ESA by itself cannot prevent the loss of many species and their habitats. Instead, the ESA is best viewed as one part of a comprehensive set of ways of protecting species and their habitats. The committee was not asked to comment on the social and political decisions concerning the ESA's goals and tradeoffs, and it has not done so. Nonetheless, they are and should be an important part of the policy discussions about the ESA.

EXTINCTIONS

Extinction is an essential part of evolution. In the past 20 years, we have learned a great deal about the earth's physical and biological history. Over the past 500 million years, at least five mass extinctions have occurred, with as much as 84% of the genera of marine invertebrates disappearing from the fossil record. Those extinctions were associated with major physical events. Today, we are again witnessing a major extinction. Unlike the earlier ones, which affected some kinds of organisms and some kinds of habitats more severely than others, today's extinctions are affecting all major groups of organisms in all nonmarine habitat types (the marine environment has not yet been affected as much as terrestrial and freshwater environments).

We do not know how many species of organisms live on earth, but there are many ways of estimating the rate of extinction in various habitats and in various kinds of organisms. The major cause of the current extinctions is human activity, and most estimates suggest that human activity has significantly increased the background extinction rate, perhaps by orders of magnitude. Such activities include direct alteration of habitats by forestry, agriculture, fishing, and residential and commercial development; indirect alteration of habitats by pollution of water, air, and the soil; alteration of ecosystems by introductions of exotic organisms and the spread of diseases; removal or alteration of sources of food and shelter for organisms by human use of natural resources, and unregulated harvesting, hunting, and fishing.

THE SPECIES CONCEPT

Species of organisms are fundamental objects of attention in all societies, and different cultures have extensive literatures on the history of species concepts. The Endangered Species Act (ESA) defines species to include "any subspecies of fish or wildlife or plants, and any distinct population segment of any species of vertebrate fish or wildlife which interbreeds when mature." In the act, the term species is used in a legal sense to refer to any of these entities. In addressing its use in the ESA, one must remember, however, that species has vernacular, legal, and biological meanings.

Many societies have notions of kinds of organisms, usually organisms that are large and conspicuous or of economic importance. The term species can be applied to many of those kinds and can be accurate as a scientific and vernacular term, because the characteristics used to differentiate species can be the same in both cases. Largely for this reason, the question of what a species is has not been a major source of controversy in the implementation of the Endangered Species Act. Greater difficulties have arisen in deciding about populations or groups of organisms that are genetically, morphologically, or behaviorally distinct, but not distinct enough to merit the rank of species--i.e., subspecies, varieties, and "distinct population segments."

In particular, questions have arisen about how to recognize "distinct population segments." To help in identifying them, the committee introduces the concept of an evolutionary unit (EU). An EU is a group of organisms that represents a segment of biological diversity that shares a common evolutionary lineage and contains the potential for a unique evolutionary future. Its uniqueness can be sought in several attributes, including morphology, behavior, physiology, and biochemistry. Because any specified group of organisms can be claimed to have a unique evolutionary future, a basic characteristic of an EU is that it is distinct from other EUs. In most cases, an EU will also occupy a particular geographical area. Most currently recognized species and subspecies are EUs.

Distinction implies an independent evolutionary future. Estimates of distinctiveness (i.e., circumscription of EUs) are based on genetic, molecular, behavioral, morphological, or ecological characteristics. Any single method will often be inadequate to identify an EU (that is, to provide compelling evidence of distinctiveness). The question of distinctiveness and the associated inference of an independent evolutionary future usually requires the careful integration of several lines of evidence.

Committee Conclusion. The ESA is clear that species and subspecies of "fish or wildlife or plants"--defined in the act to include all members of the plant and animal kingdoms--are eligible for protection. The ESA's emphasis on distinct population segments--i.e., taxa below the rank of subspecies--is soundly based on science.

Committee Recommendation. The committee concludes that the ESA's inclusion of species and subspecies is soundly justified by current scientific knowledge and should be retained. Often, competent systematists will be required to delineate subspecies, and sometimes species as well.

Committee Recommendation. To help provide scientific objectivity in identifying population segments, the concept of the evolutionary unit (EU) should be adopted. The EU is a segment of biological diversity that contains a potential for a unique evolutionary future. To clarify the analyses, identifying an EU should be separate from deciding whether it is in need of protection.

Committee Conclusion. The ESA explicitly covers species and subspecies of all plants and animals. As currently written, however, it covers taxonomic units below the subspecies level (i.e., distinct population segments) only for vertebrate animals. There is no scientific reason (other than lack of knowledge) to exclude any EUs of nonvertebrate animals and plants from coverage under the ESA. Although the way organisms are divided into kingdoms has changed since the ESA was enacted in 1973, current scientific knowledge about how species concepts apply to these organisms does not lead us to recommend that coverage be extended to prokaryotes and most single-celled eukaryotes, such as yeasts.

Committee Conclusion. Application of the EU concept should not result in any substantial change in the application of conservation laws. We hope it will move decisions of eligibility for protection away from arguments only about taxonomic ranks and into a realm where more substantive views about the degree to which populations are evolutionarily significant and new techniques can be applied.

HABITAT

Habitat--the physical setting in which organisms live and in which the other components of the environment are encountered--is a basic requirement of all living organisms. It embraces all components of a species' environment. The relationship, nationwide, between vanishing habitats and vanishing species is well documented. The ecological relationship is simple and fairly general: species diversity is positively correlated with habitat area. A corollary of this relationship is that if habitat is substantially reduced in area or degraded, species occurring in the wild will be lost. Therefore, habitat protection is a prerequisite for conservation of biological diversity and protection of endangered and threatened species. The Endangered Species Act, in emphasizing habitat, reflects the current scientific understanding of the crucial biological role that habitat plays for species.

The question has been raised whether critical habitat should be determined at the time of listing or whether it should be deferred to the time of recovery planning. Because of public concern over economic consequences, the designation of critical habitat is often controversial and arduous, delaying or preventing the protection it was intended to afford.

Committee Recommendation. Because habitat plays such an important biological role in endangered species survival, some core amount of essential habitat should be designated for protection at the time of listing a species as endangered as an emergency, stop-gap measure. As discussed below, it should be identified without reference to economic impact. Economic review may need to remain linked to critical habitat determination in the ESA, and determination of areas essential to the recovery of a species, including areas not currently occupied by that species, can be especially complex. Hence we suggest an alternative: designation of survival habitat.

Survival habitat would be designated at the time of listing of an endangered species, unless insufficient information were available or harm to the species would occur. For this purpose, survival habitat would mean the habitat necessary to support either current populations of a species or populations that are necessary to ensure short-term (25-50 years) survival, whichever is larger; survival habitat would receive the full protection that the ESA accords to critical habitat. Because of its emergency nature, no economic evaluation would be conducted before designating survival habitat. The designation of survival habitat (and its protection under the ESA) would automatically expire with the adoption of a recovery plan and the formal designation of critical habitat. Subsequent recovery planning would include designation of critical habitat as currently defined in the ESA (including economic evaluation) to include areas necessary for species recovery.

Because essential survival habitat is identified in our recommendation without reference to economic impact, and because it might not be sufficient to ensure long-term survival and recovery of endangered species, the committee views it as an emergency, stop-gap measure until critical habitat can be designated and a recovery plan can be completed, not as a substitute for those measures. Indefinite delays in designating critical habitat and formulating recovery plans after designation of survival habitat might cause harm to economic interests and to the endangered species itself. Therefore, implementation of this recommendation needs to include ways of preventing that delay from occurring.

Committee Recommendation. The committee endorses regionally based, negotiated approaches to the development of habitat conservation plans. Guidance from FWS for the development of such plans should include advice on the development of biological data, such as demographic and genetic analyses, habitat requirements of the species involved, reserve design, and monitoring, and it should also include advice on descriptions of management options and application of risk analyses in consideration of alternatives.

RECOVERY

The ultimate goal of the ESA is to recover threatened and endangered species. Recovery is "the process by which the decline of a threatened or endangered species is arrested or reversed, and threats to its survival are neutralized, so that its long-term survival in nature can be ensured." Despite increased attention from Congress, recovery plans are developed too slowly and recovery planning remains handicapped by delays in its implementation, goals that are sometimes not scientifically supported, and the uncertainty of its application to other federal activities.

No recovery plan, however good it might be, will help prevent extinction or promote recovery if it is not implemented expeditiously. Indeed, the failure to implement a recovery plan quickly can also increase the disruption of human activities, because of the resulting uncertainty among other causes.

Committee Recommendation. To reduce uncertainty and permit the planning of activities not directed at species recovery, all recovery planning should include an element of "recovery plan guidance," particularly with regard to activities anticipated to be reviewed under sections 7, 9, and 10 of the ESA. FWS should convene a working group to develop explicit guidelines for the applciation of data to the construction of recovery objectives and criteria. To the degree possible, the guidance should identify activities that can be assumed to be consistent with the requirements of those sections, activities that can be assumed to be inconsistent with them, and activities that require individual evaluation. Topics would include a habitat-based approach to recovery; a logical, hierarchical approach to analysis of ecological and genetic data on the species; guidance for demographic modeling, stressing the inherent uncertainty of such modeling; outlining future research needs and how the research will contribute to species and habitat management; and an effective monitoring scheme.

Several habitat-related features of the ESA differ without scientific basis, in particular, standards applicable to the protection of plants and to the determination of jeopardy and modification of critical habitat, and different standards of protection on public and private lands. For example, Section 9 fails to protect endangered plants from habitat modification to the same degree that it protects animals, especially on private lands.

Committee Conclusion. The biological differences between animals and plants underlying their taxonomic separation offer no scientific reason for lesser protection of plants. The biological and physical requirements of species--including endangered and threatened species--do not vary according to the ownership of the habitats that they occupy. Therefore, there is no biological reason to have different standards for determination of jeopardy, survival, or recovery on public and on private lands (there could of course be other kinds of reasons).

Committee Conclusion. Public agencies and individual public servants on public lands behave differently from private landowners, both corporations and individuals, on private lands, because their rewards and incentives are different. Therefore, requirements applied equally on private and public lands will not necessarily provide the same degree of protection, although the biological standards or criteria on which the regulations are based are the same. It follows, then, that different mechanisms may be needed for avoiding endangerment and achieving recovery on public and private lands.

Committee Conclusion. The act and its regulations distinguish between species "survival" and "recovery" for purposes of determining jeopardy to species and adverse modification of their critical habitats. Survival and recovery are points on a continuum. Clearly, if a species does not survive, it cannot recover. It is less obvious, but still true, that any action that jeopardizes recovery also decreases the probability of long-term survival.

Committee Recommendation. To permit a rational evaluation of survival and recovery goals, estimates should be provided of probabilities of achieving various goals over various periods. The periods should be expressed both in years and in generation times of the organism of concern. Evaluation of long-term and irreversible impacts should be conducted in terms of long-term recovery of the species. Although it will often be difficult to make these estimates, even the attempt to make them will have value by requiring an objective analysis and by requiring assumptions to be specified.

CONSERVATION CONFLICTS BETWEEN SPECIES

Because plants and animals are linked to other organisms in ecosystems in a variety of ways, it is inevitable that conflicts will arise when attempts are made to protect individual species of plants or animals. One of the charges presented to the committee concerned conservation conflicts between species.

Committee Conclusion. We have found few well-documented cases where management practices focusing on particular species protected under the Endangered Species Act result in direct conflict with the needs of another.

It is possible that this low number stems from lack of knowledge of the ecological networks of which threatened and endangered species are part; from the fact that comparatively few species are currently listed and that recovery plans have been formulated for even fewer; and from the inadvertent protection for other listed species under some current recovery plans. We expect that our knowledge of such conflicts and the potential for their occurrence will increase as ecologies of listed species become better known, more recovery plans are formulated, and habitat for conserving endangered species becomes more constricted.

Committee Conclusion. Under current policies, the greatest potential for conflicts in protecting species and for management of individual species will arise in situations in which habitat reductions--especially extreme reductions--themselves are the causes of endangerment and the habitats of listed species are largely overlapping.

Committee Conclusion. The most effective way to avoid conflicts resulting from management plans for individual species is to maintain large enough protected areas to allow the existence of mosaics of habitats and dynamic processes of change within these areas. In addition to, and as part of, this strategy, multispecies plans should be devised to ensure the maintenance of habitat mosaics and ecological networks. Habitat (in the broadest sense) thus plays a crucial role in protecting individual target species and, ultimately, in reducing the need for listing additional species. When insufficient habitat is available to resolve such conflicts, other factors must be evaluated to resolve the conflicts, such as the consequences of various management options on each species, the ecological importance of the species, and the distribution of the species.

ESTIMATING RISK

The concept of risk is central to the implementation of the ESA. The main risks involved in the implementation of the Endangered Species Act are the risk of extinction (related to the probability of both biological and nonbiological events) and the risks associated with unnecessary expenditures or curtailment of land use in the face of substantial uncertainties about the accuracy of estimated risks of extinction and about future events. Since the passage of the ESA, there have been enough developments in conservation biology, population genetics, and ecological theory that substantially more scientific input can now be used in the listing and recovery- planning processes. Numerous models have been developed for estimating the risk of extinction for small populations. Although most of these models have shortcomings, they do provide valuable insights into the potential impacts of various management (or other) activities and of recovery plans. In particular, they are valuable for comparing the likely effects of alternative management options and of alternative adverse effects on the species.

Despite the major advances that have been made in models for predicting mean extinction times, the existing methods still have substantial limitations. Often, risk factors are not well known. Most of the models deal with only one risk factor at a time and fail to incorporate the interactive effects of multiple risk factors on reducing the time to extinction. This might result in a tendency for such models to underestimate the risk of extinction. Efforts to integrate various sources of random variation (genetic, demographic, and environmental) into spatially explicit frameworks are badly needed.

Most extinction models primarily address the mean time to extinction. Because decisions associated with endangered species usually are couched in fairly short time frames--less than 100 years--models that predict the cumulative probability of extinction through various time horizons would have greater practical utility than current models.

Committee Conclusion. With only a few exceptions, biologically explicit, quantitative models for risk assessment have played only a minor role in decisions associated with the ESA. They should play a more central role, especially as guides to research and as tools for comparing the probable effects of various environmental and management scenarios.

Committee Conclusion. Results from population- genetic theory provide the basis for one fairly rigorous conclusion. Small population sizes usually lead to the loss of genetic variation, especially if the populations remain small for long periods. If the members of the population do not mate with each other at random (the case for most natural populations), then the effect of small size on loss of genetic variation is made more severe; the population is said to have a smaller effective size than its true size. Populations with long- term mean effective sizes greater than approximately 1,000 individuals can be viewed as genetically secure; any further increase in effective size would be unlikely to increase the amount of adaptive variation in a population. Because the effective population size is usually substantially smaller than actual population size, this conclusion translates into a goal for long-term survival for most species of maintaining populations with more than a thousand mature individuals per generation, perhaps several thousand in some cases. An appropriate, specific estimate of the number of individuals needed for long-term survival of any particular population should be based on knowledge of the population's breeding structure and ecology. If information on that species is lacking, information about a related species might be useful.

MAKING ESA DECISIONS IN THE FACE OF UNCERTAINTY

To ensure that ESA decisions protect endangered species as they are intended to in a scientifically defensible way requires objective methods for assessing risk of extinction and for assigning species to categories of protection according to that risk. Standards for assigning species to categories should be quantitative wherever possible and, when this is not possible, qualitative procedures should at least be systematic and clearly defined. Major advances in both theory and methods of estimating risk of extinction allow us to base listing and recovery decisions on scientific principles. In the past, many ESA decisions have failed to meet the guidelines suggested by current scientific thinking, listing species as endangered only when populations had dropped to the point where extinction was imminent and proposing recovery goals that left the species still at high risk of extinction.

Committee Conclusion. We can find no scientific basis for setting different levels of risk for different taxonomic groups, such as plants or animals, or for public versus private actions that may affect listed species. However, it is critical to understand that because public and private entities may behave differently, different management policies may be required for public and private lands in order to achieve the same biological risks for listed species in the two settings. No implementation of the ESA can be fully successful without recognizing these differences.

Committee Recommendation. To the degree that they can be be quantified, the levels of risk associated with endangered status should be higher than those for threatened status. Once a species no longer qualifies for threatened status, it should be considered recovered and delisted. Levels of risk to trigger ESA decisions should be framed as a probability of extinction during a specified period (i.e., x% probability of extinction over the next y years). Although some crises may call for short time horizons (on the order of tens of years), ordinarily it will be necessary to view extinction over longer periods (on the order of hundreds of years) so that short-term solutions do not create long-term problems. The selection of particular degrees of risk associated with particular periods as the standards for listing species as endangered or threatened reflects both scientific knowledge and societal values.

Although the objectives of the ESA are not intrinsically conflicting, the act must be implemented with limited budgets, and so conflicts can arise in determining how to allocate funds among listed species, all of which qualify for the act's protection. Scientific considerations, such as whether a species or its habitat possesses unusually distinctive attributes or whether protection of a taxon would confer protection on other candidate taxa and their habitats, should be used to help set priorities for action. Decisions to set priorities for implementation of the act are often difficult and controversial, and the procedures for making them should be explicit and well documented. Structured methods, such as decision analysis, can improve both the substance of these decisions and the justifications offered for them.

Meeting the objectives of the act can sometimes conflict with other human objectives, such as development of private or public property harboring listed species. The act prohibits consideration of human objectives unrelated to species protection in decisions regarding listing, "take," and "jeopardy," but directs that these other objectives be taken into account in decisions about critical habitat and implementation of recovery plans. Tradeoffs between species protection and economic or other benefits or costs must be evaluated. Again, because these tradeoff decisions are often difficult and controversial, it is important to use well-structured and explicit methods for making them.

ESA decisions are inevitably based on limited information, and so agencies are obliged to act in the face uncertainty about species status and the impacts of proposed activities. Decisions in the face of uncertainty carry the prospect of being wrong in various ways and with varying, and often asymmetrical, consequences. For example, managers concerned with delisting a formerly endangered species must be wary of two types of errors: delisting when the species is actually still in peril, and failing to delist when the species has truly recovered to the target level. Each type of error has both biological and nonbiological consequences. The first error has adverse biological consequences for the endangered species--it would be irreversible if the species became extinct--and, perhaps, positive socioeconomic consequences for sectors whose activities may have been constrained by recovery guidelines. The second error has neutral to positive consequences for the species but potential negative socioeconomic consequences. It is not possible to minimize the risks of both types of errors simultaneously. A decision rule that guards against the first will allow too many of the second and vice versa. To set acceptable rates for each type of error, both the likelihood and the magnitude of biological and nonbiological benefits and costs must be weighed in a decision-analytic framework. These decisions are too complicated and too consequential to be entrusted to unaided intuition.

If not examined explicitly, this asymmetric error structure can bias decisions under the act to the detriment of endangered species, especially if they are based on analyses that do not take the asymmetric risk function into account. Although the wording of the ESA suggests that the "burden of proof" to show no effect is on those proposing to modify habitat or harm a listed species, the way that hypothesis tests are phrased and error rates are set can put the burden on those attempting to show that a species should be listed or that a development proposal should be denied or modified.

Committee Recommendation. Because the structure of hypothesis testing related to listing and jeopardy decisions can make it more likely for an endangered species to be denied needed protection than for a nonendangered species to be protected unnecessarily, decisions under the act should be structured to take explicit account of all the types of errors that could be made and their consequences, both biological and nonbiological. The phrasing of the null hypothesis and setting of error rates should reflect societal, as well as scientific, judgments about what level of risk is acceptable for which types of errors.

TIMING

The committee's comments on the timing of key decisions under the ESA are incorporated in discussions of various other topics. In particular, timing is considered in discussions of recovery planning (where the committee concludes that recovery plans are developed too slowly and recovery planning remains handicapped by delays in implementation) and identification of survival habitat (whose designation is recommended to overcome the effects of delays in designation of critical habitat).

BEYOND THE ENDANGERED SPECIES ACT

The Endangered Species Act's goal is the prevention of species extinction, and its legal apparatus to protect endangered species is strong. It does not appear to have been intended as an overall policy act for the preservation of all of the nation's ecosystems and biota. It is, as the committee understands it, intended as a safety net.

Committee Conclusion. Although it is impossible to quantify the ESA's biological effects--i.e., how well it has prevented species from becoming extinct--the committee concludes that fewer species have become extinct than would have without the ESA. In other words, the ESA has successfully prevented some species from becoming extinct. Retention of the ESA would help to prevent species extinction. Some changes, as outlined in this report, would probably make the act more effective and predictable, and provide a more objective basis for its implementation.

Committee Conclusion. It is also clear that some species have become or are almost certain to become extinct despite the protection of the ESA. In other words, the ESA cannot by itself prevent all species extinctions, even if it is modified. Therefore, the committee concludes that additional approaches to the management of natural resources will need to be developed and implemented as complements to the ESA to prevent the continued, accelerating loss of species. Indeed, many federal, state, and local governments and private organizations are developing such approaches.

• Ecosystem management. Despite diverse definitions of ecosystem management and despite scientific uncertainties, it is clear that managing ecosystems and landscapes as an addition to the protection of individual species can lead to improved natural-resource management and can help reduce species extinctions. Properly implemented, it can also help to reduce uncertainty and thus reduce economic disruptions.

• Reconstruction or rehabilitation of ecosystems. Restoration ecology is a growing discipline. Many ecosystems functions have been improved or restored by such activities, and reconstruction or rehabilitation of ecosystem functioning holds much promise for the protection of endangered species. It is not usually possible to return an ecosystem to some prior pristine condition, however. Many ecosystems have been so altered that it is difficult to decide what prior condition we might want to return to. The trajectory taken by the ecosystem to get to its current condition is not retraceable in the way that a highway is, because many events occur in an ecosystem's history that are not precisely reversible. Genetic variability is lost; evolution occurs; exotic species are introduced; human populations in the region increase, and people develop dependence on a variety of modern technologies, cultures, and economic systems; and other natural and anthropogenic environmental changes affect the range of biophysical and socioeconomic possibilities for future states of the system. In brief, the past provides opportunities for the future but also constrains it. Thus, attempts to rehabilitate ecosystem functioning should keep these constraints in mind, so that inappropriately high expectations are not generated.

• Mixed management plans. Often, resource managers manage areas either for protection of biota or for human use. It is increasingly difficult to keep people and the effects of their activities separate from wildlife sanctuaries. Although such sanctuaries (e.g., national parks, wilderness areas, wildlife refuges, marine sanctuaries) are indispensable for protecting endangered species, greater attention needs to be paid to developing mixed-use areas. These would be urban recreation areas or residential and commercial developments adjacent to untrammeled areas designed to improve opportunities for wildlife while maintaining opportunities for human activities. Although the value of this approach is becoming increasingly recognized, its development is still in the early stages.

• Cooperative management. Various experiences with cooperative management--the sharing of planning and decision making by various government and nongovernment groups--have had some success. To some degree, habitat conservation plans represent an example of this approach, but it is likely that cooperative management will be necessary in cases where the strict requirements of the Endangered Species Act have not yet been applied. It is important to include the major interested parties without having so many interests involved that consensus is difficult to reach.

• Revised economic accounting. Too often, economic calculations underlying public and private decision making are incomplete. Often, they cover too short a time span, and they often exclude nonmarket values. A short-term loss might turn into a long-term gain: for example, losing an economic activity today might provide opportunities for greater economic activities of different types at some time in the future. Again, the validity of expanding economic accounting to cover longer periods and to include nonmarket values is becoming more widely recognized but it is still in the early stages of development.

SCIENCE, POLICY, AND THE ESA

This committee was asked to review the scientific aspects of the ESA and it has done so. It has not uncovered any major scientific issue that seriously hinders the implementation of the act, although its review has suggested several scientific improvements. Many of the conflicts and disagreements about the ESA do not appear to be based on scientific issues. Instead, they appear to result because the act--in the committee's opinion designed as a safety net or act of last resort--is called into play when other policies and management strategies or their failures, or human activities in general, have led to the endangerment of species and populations. In some cases, policies and programs have been based on sound science, but other factors have prevented them from working. The committee does not see any likelihood that those endangerments will soon cease to occur or that the ESA can or should be expected to prevent them from occurring. It therefore concludes that any coherent, successful program to prevent species extinctions and to protect the nation's biological diversity is going to require more enlightened commitments on the part of all major parties to achieve success.

To conserve natural habitats, approaches must be developed that rely on cooperation and innovative procedures; examples provided for by the ESA are habitat conservation plans and natural community consevration planning. But those are only a beginning. Many other approaches have been discussed in various fora. They include cooperative management (sharing decision-making authority among several governmental and nongovernmental groups), transfer of development credits, mitigation banks, tax incentives, and conservation easements.

An analysis of these and other policy and management options is beyond this committee's charge, but sound science alone will not lead to successful prevention of many species extinctions, conservation of biological diversity, and reduced economic and social uncertainty and disruption. But sound science is an essential starting point. Combined with innovative and workable policies, it can help to solve these and related problems.

Michael T. Clegg, Ph.D.* (chair)
Dean, College of Natural and Agricultural Sciences, and
Professor of Genetics
University of California
Riverside

Gardner M. Brown Jr., Ph.D.
Professor of Economics and Adjunct Professor
Institute for Environmental Studies
University of Washington
Seattle

William Y. Brown, Ph.D., J.D.
Principal
RCG/Hagler Bailly Inc.
Arlington, Va.

William L. Fink, Ph.D.
Associate Curator of Fishes, Museum of Zoology, and
Associate Professor
University of Michigan
Ann Arbor

John Harte, Ph.D.
Professor of Soil Science and Energy and Resources
University of California
Berkeley

Oliver A. Houck, J.D.
Professor of Law
Tulane University
New Orleans

Michael Lynch, Ph.D.
Director
Ecology and Evolution Program
University of Oregon
Eugene

Lynn A. Maguire, Ph.D.
Associate Professor
Practice of Environmental Management
Duke University
Durham, N.C.

Dennis D. Murphy, Ph.D.
Director, Center for Conservation Biology, and
Senior Research Associate
Stanford University
Stanford, Calif.

Patrick V. O'Brien, Ph.D.
Team Leader, Ecology
Chevron Research and Technology Co.
Richmond, Calif.

Steward T.A. Pickett, Ph.D.
Member, Rutgers Graduate Ecology Faculty;
Adjunct Professor, University of Connecticut; and
Scientist, Institute of Ecosystem Studies
Millbrook, N.Y.

Katherine Ralls, Ph.D.
Research Zoologist
Smithsonian Institution
Washington, D.C.

Beryl B. Simpson, Ph.D.
Chair and Professor of Botany
Department of Botany
University of Texas
Austin

Rollin D. Sparrowe, Ph.D.
President
Wildlife Management Institute
Washington, D.C.

David W. Steadman, Ph.D.
Senior Scientist and Curator of Birds, New York State Museum and Biological Survey, and
Adjunct Curator of Fossil Birds, Burke Memorial Museum
University of Washington
Seattle

James M. Sweeney, Ph.D.
Manager of Wildlife Issues
Champion International Corp.
Washington, D.C.

David Policansky, Ph.D.
Study Director

Source: National Academy of Sciences
Last update: 5/24/95