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SCIENCE AND THE
ENDANGERED SPECIES ACT
Committee on Scientific Issues in
the Endangered Species Act
Board on Environmental Studies and Toxicology
Commission on Life Sciences
1995
National Research Council
PREPUBLICATION COPY
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NATIONAL ACADEMY PRESS
010.
2101 Constitution Ave., N.W. Washington, D.C. 20418
NOTICE: The project that is the subject of this report was approved by the Governing Board of the
National Research Council, whose members are drawn from the councils of the National Academy
of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of
the committee responsible for the report were chosen for their special competences and with regard
for appropriate balance.
This report has been reviewed by a group other than the authors according to procedures ap-
proved by a Report Review Committee consisting of members of the National Academy of Sciences,
the National Academy of Engineering, and the Institute of Medicine.
The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distin-
guished scholars engaged in scientific and engineering research, dedicated to the furtherance of
science and technology and to their use for the general welfare. Upon the authority of the charter
granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal
government on scientific and technical matters. Dr. Bruce Alberts is president of the National
Academy of Sciences.
The National Academy of Engineering was established in 1964, under the charter of the
National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous
in its administration and in the selection of its members, sharing with the National Academy of
Sciences the responsibility for advising the federal government. The National Academy of
Engineering also sponsors engineering programs aimed at meeting national needs, encourages
education and research, and recognizes the superior achievements of engineers. Dr. Robert M. White
is president of the National Academy of Engineering.
The Institute of Medicine was established in 1970 by the National Academy of Sciences to
secure the services of eminent members of appropriate professions in the examination of policy
matters pertaining to the health of the public. The Institute acts under the responsibility given to the
National Academy of Sciences by its congressional charter to be an adviser to the federal government
and, upon its own initiative, to identify issues of medical care, research, and education. Dr. Kenneth
I. Shine is president of the Institute of Medicine.
The National Research Council was organized by the National Academy of Sciences in 1916
to associate the broad community of science and technology with the Academy's purposes of
furthering knowledge and advising the federal government. Functioning in accordance with general
policies determined by the Academy, the Council has become the principal operating agency of both
the National Academy of Sciences and the National Academy of Engineering in providing services
to the government, the public, and the scientific and engineering communities. The Council is
administered jointly by both Academies and the Institute of Medicine. Dr. Bruce Alberts and
Dr. Robert M. White are chairman and vice chairman, respectively, of the National Research
Council.
The project was supported by the Department of the Interior Contract No. 14-48-0009-92
Copyright 1995 by the National Academy of Sciences. All rights reserved.
Printed in the United States of America
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COMMITTEE ON SCIENTIFIC ISSUES IN THE ENDANGERED
SPECIES ACT
MICHAEL T. CLEGG (ChairJ, University of California, Riverside, Calif.
GARDNER M. BROWN, JR., University of Washington, Seattle,Wash.
WILLIAM Y. BROWN, RCG/Hagler Bailly Inc., Arlington, Va.
WILLIAM L. FINK, University of Michigan, Ann Arbor, Mich.
JOHN HARTE, University of California, Berkeley, Calif.
OLIVER A. HOUCK, Tulane University, New Orleans, La.
MICHAEL LYNCH, University of Oregon, Eugene, Oreg.
LYNN A. MAGUIRE, Duke University, Durham, N.C.
DENNIS D. MURPHY, Stanford University, Stanford, Calif.
PATRICK V. O'BRIEN, Chevron Research & and Technology Company,
Richmond, Calif.
STEWARD T. A. PICKETT, Institute of Ecosystem Studies, Millbrook, N.Y.
H. RONALD P - SIAM, University of Georgia, Athens, Gal, resigned 5/31/94
KATHERINE RALLS, Smithsonian Institution, Washington, D.C.
BERM B. SIMPSON, University of Texas, Austin, Tex.
ROLLIN D. SPARROWE, Wildlife Management Institute, Washington, D.C.
DAVID W. STEADMAN, New York State Museum, Albany, N.Y.
JAMES M. SWEENEY, Champion International Corporation,Washington, D.C.
Stab:
DAVID J. POEICANSKY, Project Director
PATRICIA PEACOCK, Staff Officer (until 02/03/95)
LEE PAULSON, Editor
ADRIENNE DAVIS, Sr. Project Assistant
Sponsor: U.S. Department of the Interior
· . .
111
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BOARD ON ENVIRONMENTAL STUDIES AND TOXICOLOGY
PAUL G. RISSER (Chair), Miami University, Oxford, Ohio
MICHAEL J. BEAN, Environmental Defense Fund, Washington, D.C.
EULA BINGHAM, University of Cincinnati, Cincinnati, Ohio
EDWIN H. CLARK II, Clean Sites, Inc., Alexandria, Va.
ALLAN H. CONNEY, Rutgers University, Piscataway, N.J.
ELLIS COWLING, North Carolina State University, Raleigh, N.Car.
JOHN L. EMMERSON, Eli Lilly & Company, Greenfield, Ind.
ROBERT C. FORNEY, Unionville, Pa.
ROBERT A. FROSCH, Harvard University, Cambridge, Mass.
KA} LEE, Williams College, Williamstown, Mass.
JANE LUBCHENCO, Oregon State University, Corvallis, Ore.
GORDON ORIANS, University of Washington, Seattle, Wash.
FRANK L. PARKER, Vanderbilt University, Nashville, Tenn.
GEOFFREY PLACE, Hilton Head, S. Car.
DAVID P. RALL, Washington, D.C.
LESLIE A. REAL, Indiana University, Bloomington, Ind.
KRISTIN SHRADER FRECHETTEq University of South Florida, Tampa, Fla.
BURTON H. SINGER, Princeton University, Princeton, N.J.
MARGARET STRAND, Bayh, Connaughton & Malone, Washington, D.C.
GERALD VAN BELLE, University of Washington, Seattle, Wash.
BAILUS WALKER, JR., Howard University, Washington, D.C.
Staff
JAMES J. REISA, Director
DAVID J. POLICANSKY, Associate Director and Program Director for Natural
Resources and Applied Ecology
CAROL A. MACZKA, Program Director for Toxicology and Risk Assessment
LEE R. PAULSON, Program Director for Information Systems and Statistics
RAYMOND A. WASSEL, Program Director for Environmental Sciences and
. . .
. ~ngmeermg
IV
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COMMISSION ON LIFE SCIENCES
THOMAS D. POLLARD (Chair), Johns Hopkins Medical School, Baltimore,
Md.
BRUCE N. AMES, University of California, Berkeley, Calif.
JOHN C. BAILAR III, McGill University, Montreal, Quebec
MICHAEL BISHOP, Hooper Research Foundation, University of California
Medical Center, San Francisco, Calif.
JOHN E. BURRIS, Marine Biological Laboratory, Woods Hole, Mass.
MICHAEL T. CLEGG, University of California, Riverside, Calif.
GLENN A. CROSBY, Washington State University, Pullman, Wash.
MARIAN E. KOSHLAND, University of California, Berkeley, Calif.
RICHARD E. LENSKI, Michigan State University, East Lansing, Mich.
EMIL A. PFITZER, Hoffmann-La Roche Inc., Nutley, N.J.
MALCOLM C. PIKE, University of Southern California School of Medicine,
Los Angeles, Calif.
HENRY C. PITOT, III, University of Wisconsin, Madison, Wisc.
JONATHAN M. SAMET, The Johns Hopkins University School of Medicine,
Baltimore, Md.
HAROLD M. SCHMECK JR., Armonk, N.Y.
CARLA J. SHATZ, University of California, Berkeley, Calif.
SUSAN S. TAYLOR, University of California at San Diego, La Jolla, Calif.
P. ROY VAGELOS, Merck & Company, Whitehouse Station, N. J.
JOHN L. VANDEBERG, Southwestern Foundation for Biomedical Research, San
Antonio, Tex.
PAUL OILMAN, Executive Director
v
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Preface
The Endangered Species Act (ESA) is an important legislative too! for the protection of
threatener} and endangered species in the Uniter! States. The ESA asserts a legal claim on behalf of
those species in the United States to habitat that sometimes conflicts with competing management
goals for both private and public lands. It is inevitable that these conflicts play out in the political
arena. Our committee was asked to provide advice on scientific aspects of the ESA and to consider
whether the act is "protecting endangered species ant] their habitats." We have endeavored! to restrict
our advice to the areas where science can better inform the public policy debate. The distinction
between science and public policy is often fuzzy, because the possession of scientific knowledge and
the implementation of that knowledge are so closely linked. Our goal in this report has been to
explore ant! illuminate the knowledge sicle of the equation.
Since the original passage of the ESA in 1973, scientific knowledge has been anything but
static. Our understancling of biological species, in terms of their genetic and phylogenetic integrity,
has greatly expanded since 1973. A rich array of new experimental tools have been acquired from
both genetics and computational biology cluring the past two clecacles and these have helped to drive a
revolution in the traditional sciences of taxonomy and systematics. At the same time, new theoretical
constructs have been elaborated that have given greater depth to definitions of species.
Species are composed of systems of populations (metapopulations) that have both temporal
and spatial dimensions. The temporal history of individual species and of the migrating continental
lane! masses that contain terrestrial habitats is known in much greater detail today than in 1973. The
earth is dynamic and contemporary biological (liversity is the unique realization of this long history of
change. The time scales involved in biological change are long relative to human generations anal, as
a consequence, it is easy for us to see the biological world as static. Nothing could be further from
the truth. Modern biology reveals that species are reservoirs of unique genetic adaptations to
multifaceted physical ant! biological environments. The accumulation of these diverse adaptations is
the result of a shared evolutionary history that typically involves hundreds of thousands of years of
genetic continuity. The extinction of a species constitutes the irreversible loss of a suite of unique
genetic adaptations that have been acquired (much like interest) over a long history of investment.
Rates of extinction are uneven over geological time. Several episodes of major extinction are
now recognized including the Permian-Triassic event (245 million years ago) when approximately
65 % of terrestrial species became extinct and the Cretaceous-Tertiary event (65 million years ago)
when approximately 90% of terrestrial and marine reptiles became extinct. When viewed on a global
scale, the present era constitutes yet another major episode of biological extinction. In contrast to the
past, however, the present cause of extinction is a single biological species that has become so
successful and so exploitive that it threatens to destroy the very capital that is necessary for its own
long-term survival. That single species humankind is capable of rational analysis and planning, so
that it can influence its own long-term destiny.
The earth's non-human biota is crucial to humans' long-term survival. We depend on the
photosynthetic capability of green plants for the oxygen that we breathe and for virtually all of our
food and energy requirements. The ability of green plants to grow is in turn dependent on a fixed
supply of nitrogen (nitrates and nitrites) that are largely the product of a specialized group of
microorganisms (Rhizobia). Many of our modern drugs have been derived from biotic sources. The
list of human dependencies on the complex web of biological species is virtually endless.
Habitat, the spatial dimension of species, is absolutely crucial to species survival. Habitat is
the theater in which the network of interactions between the physical and biological worlds play out.
. .
V11
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The landscape theory of habitat emphasizes the heterogeneity, complexity and dynamic character of
the physical and biological environment. The metapopulations of species are distributed on this
shifting mosaic. If these are the scientific realities, then how do we match science to wise habitat
conservation?
The authors of the ESA recognized that species conservation must include strong provisions
for habitat conservation. These provisions included a trigger (threatened or endangered status of a
species) that caused certain legal prohibitions (jeopardy and taking restrictions). The law provides for
the recovery of species through the designation of critical habitat and through the elaboration and
implementation of recovery plans. During the 20-year evolution of the ESA, additional provisions
have been acIded, including acIditional mechanisms for habitat conservation, ant! others aimed at the
resolution of conflicts engendered by ESA prohibitions. The committee was not charger! with
reviewing how the ESA is implemented by various federal agencies and ctid not directly address this
question. We do, however, have several recommendations that would help improve the
administration of the ESA if they were adopted (see Chapters 4 and 10, for example).
In general our committee finds that there has been a goo~i match between science ant! the
ESA. There are, of course, points where the agreement between science and the ESA is poorer.
These include lack of timely designation of enciangerec! or threatened status and similarly timely
removal from these categories when recovery goals have been achieved. Survival habitat should be
identified and designates! for protection if necessary when species are listed as endangered. We have
been able to align the "distinct population segment" language of the ESA with our contemporary
understanding of evolutionary units. We hope that such alignment helps to achieve Congress's intent
that distinct population segments be listed only sparingly and on a sound scientific basis and thus
reduces the clanger that the ESA itself could be jeopardized by carrying that language to an absurd
extreme.
The analytical tools to evaluate species health have been greatly developed in recent years.
The emergence of extinction theory from population genetics and ecology, the combination of
demography and genetics in population viability analysis and the extension of risk analyses into the
realm of biological conservation promise to leac! us to wiser allocations of effort in the future. The
field of ecosystem management has also emerged as a significant field of applied biology, in part as a
response to the need for a more global view of conservation imperatives. The rich growth of these
areas of science has also illuminated areas where our knowledge is still inadequate. in response to the
charges given our committee, we attempt to identify areas of critical scientific uncertainty.
To paraphrase the great 20th century ecologist G. E. Hutchinson, species are the actors in the
ecosystem theater. To sustain a viable future for our descendants, we must find ways to preserve
both species and ecosystems. The ESA is a critically important part of our efforts to conserve species
. .- . . ~ · . ~ .. . . - . . . · . - .. . . .
and thereby conserve ecosystems. By virtue of the habitat restrictions that accompany endangered
status, species that happen to share habitat with an endangered species gain a measure of protection.
The 20-year history of the ESA has validates! its focus on species endangerment. Species are
objective entities that are easily recognized. Their health and needs can be assessed and sound
scientific management plans can be implemented. Despite this, the task of managing each of the vast
multitude of species on a case-by-case basis is beyond human capabilities. This is further
compouncled by the fact that many species remain undescribeci. A challenge for the future is to find
more integrated mechanisms to sustain both species and ecosystems that do not depend on case-by-
case management.
It was my great good fortune to work with a knowledgeable, effective, and collegial
committee. The various chapters of this report are the product of much hard work and spirited
debate. I want to express my creep gratitude to the committee including H. Ronald Pulliam, who
resigned from the committee when he assumed the directorship of the National Biological Service in
. . .
v'''
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May 1994 for their wisdom, patience and cheerful acceptance of the tasks imposed by this project.
On behalf of the committee, I thank Project Assistant Acirienne Davis for attending to our many
needs. Staff Officer Patricia Peacock was a source of much practical experience in conservation
policy and she was a diligent editor and critic. Project Director David Policansky contributed his vast
experience in science policy, especially in the realm of conservation policy, to this project. David
Policansky ant! Pat Peacock also wrote, rewrote and edited many sections of this report. They
contributed greatly to the finished product. Finally, thanks to the many representatives of public
agencies especially the Fish and Wilcllife Service and private groups who made written and oral
presentations to our committee. They added an essential dimension to our understanding of the
complex issues that surround the ESA.
Michael T. Clegg
Chairman
.
IX
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Contents
Executive Summary
Chapter I. :Introduction
History
The Present Study
References
Chapter 2. Species Extinctions
Extinctions Over Geological Time
Prehistoric Human Impact on Continental Ecosystems
Prehistoric Human Impact on Islanc! Ecosystems
Relating the Past to the Present
References
Chapter 3. Species Definitions and the Endangered Species Act
Historical Use of the Term Species in Implementation of
the Endangered Species Act
History of Species Concepts Before and After the Endangered Species Act
A Concept of Species for the Purposes of the ESA
References
Chapter 4. The Role of Habitat Conservation and Recovery Planning
The Importance of Habitat
The Role of Habitat Conservation Under the ESA
Critical Habitat and Federal Activities
Private Activities ant} Habitat Conservation Planning
Habitat-Conservation Plans
Recovery Planning
Natural Communities Conservation Planning Program and Coastal
Sage Scrub Community of Southern California
Habitat-Related Standar~is
Conclusions anti Recommenciations
References
Chapter 5. Modern Perspectives of Habitat
Landscapes and Populations
Sources and Sinks
Metapopulations
Spatially Explicit Moclels
A Spatial Perspective ant! Population Viability Analysis
Conclusions
References
Chapter 6. Conservation Conflicts Between Species
Interactions of Species in Nature
Xl
1
13
13
15
16
19
19
20
23
24
30
37
37
40
44
53
57
57
58
60
61
62
63
66
70
71
72
75
77
77
78
79
81
82
83
89
89
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Northern Goshawk and Mexican Spotted Owl
WinterRun Chinook Salmon ant! Delta Smelt
Bachman's Sparrow and RecICockacled Woodpecker
Marine Mammals and Salmonicis
Conclusions
Recommendations
References
Chapter 7. Estimating Risk
Estimating The Risk of Extinction
Sources of Risk
Limitations of Our Ability to Estimate Risk
Conclusions anti Recommendations
References
Chapter S. Making ESA Decisions in the Face of Uncertainty
Decisions Required Uncler the ESA
The Need for New Approaches to Decision Making
Providing Objective Risk Standards
Using Structured Approaches to Decision Making
Conclusions anti Recommendations
References
Chapter 9. Areas of Scientific Uncertainty
Ecosystem-Based Protection
Ecosystem Management
Inadequate Knowledge of Species and Their Roles in Ecosystems
Estimation of the Risk of Extinction
Lack of Basic Information
The Protection of Genetic Diversity
Feasible Managment Strategies
Valuing Rarity
References
Chapter 10. Beyond the Endangered Species Act
Is the ESA Working?
Reducing Extinction
Recovery Success
Protection of Ecosystems
The Future: Beyond the Enclangere(1 Species Act
Science, Policy, ant! the ESA
References
APPENDIX A Letter from Congress Requesting ESA Stucly
APPENDIX B Endangered Species Act
APPENDIX C Biographical Information on Committee and Staff
. .
X11
90
90
93
94
96
96
97
99
99
99
111
112
113
117
117
117
119
123
137
138
143
143
144
144
144
145
146
147
148
151
155
155
155
156
158
159
161
162
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