I. Introduction
The Endangered Species Act, as amended in
1988, has three purposes: "...to provide a means whereby the
ecosystems upon which endangered species and threatened species depend may
be conserved. ...to provide a program for the conservation of such
endangered species and threatened species." ...to take such steps as
may be appropriate to achieve the purposes of the treaties and
conventions..." (Endangered Species Act 1988). By enacting the
Endangered Species Act of 1973, Congress, on behalf of the American
people, established a national goal and commitment to protect the Nation's
biological resources. The Act establishes the form and sequence for the
process of providing federal protection, from listing threatened and
endangered species to the implementation of their recovery. The Act is a
powerful and sensible way to protect biological diversity that specifies
the procedures and mechanisms to achieve that goal. However, the original
legislation and subsequent amendments to the Act do not explicitly specify
how science will be used to carry out the legislative mandate. Instead,
the manner in which scientific knowledge is to be used is largely left to
the discretion of the implementing agencies, the United States Fish and
Wildlife Service and National Marine Fisheries Service. The goals of the
Act are to identify species that are at risk of extinction, to implement a
process for reducing that risk by limiting additional sources of jeopardy,
and to develop and implement a recovery program. The process is flexible
and can be applied to individual species or to groups of species that
share an ecosystem or management area. If the valuable scientific
knowledge that has accumulated over the past several decades of analytical
ecological research is used to the fullest extent, the Act can become an
even more powerful tool in achieving the societal goals for which it was
enacted. The Act has improved the status of some species, such as the
California sea otter, peregrine falcon, American alligator, whooping
crane, and bald eagle. Nevertheless, each year, many more species are
added to the list of endangered species than are successfully recovered
and removed from the list. Despite being protected, some species are
becoming extinct. Currently 955 species in the U.S. are on the list of
endangered and threatened species; only slightly more than half of them
have approved recovery plans (Department of the Interior 1995). Given this
growing list of threatened and endangered species and the limited success
in recovery of endangered species, the Ecological Society of America
undertook an analysis of the Endangered Species Act, with the objective of
assessing how the Act could be made more effective through better use of
scientific information. The nation's biological diversity has great
economic, aesthetic, and spiritual value. Modern society draws upon
biological diversity as a source of medicines, fiber, food, as sources of
genes for future incorporation into crop plants, and for uses we cannot
predict. The extensive services that natural ecosystems provide, such as
cleansing of air and water, control of erosion, and stabilization of
climate, depend in part on the richness of species in those systems.
Therefore, the Ecological Society's analysis accepts and supports the
goals and objectives of preserving the biological heritage of the United
States and explores how science can be used more effectively than it has
in the past to enhance the achievement of those goals.
II. The Implementation
Processes of the Endangered Species Act
The Endangered Species Act sets out a series
of steps for determining whether a species is at risk of extinction,
removing the major causes of its endangerment, and returning the species
to a viable state. The major stages in this process are: (1) Listing a
species as threatened or endangered, (2) designating the habitat that is
critical for survival of the species, (3) providing immediate protection
and prohibition of acts that would further jeopardize the species, (4)
developing and implementing recovery plans, and (5) delisting the species
once it has been restored to a viable state. Scientific information must
be used at all of these stages if an accurate initial assessment and a
successful recovery program are to be achieved. The process of listing a
species includes a series of steps that begins with a decision to propose
a species as a candidate for protection and culminates in one of three
outcomes: rejection of the claim for protection; inclusion of the species
under federal protection as either an endangered or threatened species; or
placing the species in an ill-defined category, known as "warranted,
but precluded." Although decisions on status of species designated
"warranted, but precluded" are to be made within a 12 month
finding period, since 1982, 114 species have remained in this category for
two or more years. Fifty-six have been in this category for at least 8
years (GAO 1992). Once a species is listed, the Endangered Species Act
requires the designation of "critical habitat." In the
legislative language, "critical habitat" is defined as the
minimal area that is needed to supply the species with its immediate
survival needs. The Endangered Species Act also provides immediate
protection to a species when it is listed as threatened or endangered.
Section 7 of the Act requires all federal agencies to ensure that any
actions they authorize, fund, or carry out do not jeopardize the continued
existence of any listed species or adversely modify its habitat. Thus,
every federal agency must examine whether any action it proposes to carry
out might adversely affect a listed species and these assessments must be
scrutinized and evaluated by the Fish and Wildlife Service or the National
Marine Fisheries Service. Scrutiny occurs through a process known as
"formal consultation" and ends with a written "biological
opinion" containing the service's views. These opinions are not
legally binding on the other federal agency but federal agencies are
reluctant to proceed with a project in the face of a jeopardy opinion
because the probability that a citizen suit will be brought against the
action is very high. In such suits, jeopardy opinions are given
considerable weight by the courts. Formal consultations serve other
purposes in addition to making jeopardy determinations. They also search
for reasonable alternatives or adjustments to the proposed action that
could avoid jeopardizing a listed species. Section 7 also deals with
incidental take, which is defined as a taking of a listed species that is
incidental to, and not the primary purpose of, otherwise lawful
activities. The term "take" refers to many possible
perturbations to the species, including "harm, harass, kill, wound,
catch," etc, all of which are prohibited under the Act unless
authorized by a permit, an incidental take statement, or a special rule.
Incidental take has been interpreted to include harm to the habitat of a
species as well as direct harm to the species itself, and this
interpretation has been upheld in a 1995 Supreme Court decision. From a
scientific standpoint, degradation or destruction of the habitat of a
species can be at least as harmful to the survival of the species as
direct injury to an individual of the species. In 1982 Congress amended
the Act to provide mechanisms for regulating incidental take on
non-federal land. Those procedures are now found in section 10(a)(1)(B).
Persons applying for an incidental take permit under Section 10(a)(1)(B)
must submit a "Habitat Conservation Plan" or HPC along with
other materials attendant to their permit application. In the case of
Section 7, "harm" is defined as an action that significantly
reduces both the survival and recovery of a species. Similarly, in the
definition of harmful destruction of critical habitat, a jeopardy ruling
requires that both the survival and recovery of a species be affected.
Many actions slow a recovery process but it is difficult to show
unambiguously that an action threatens the survival of a species (Rohlf
1989). When a species is listed, the Endangered Species Act requires that
a recovery plan be developed. The ultimate goal of the recovery plan is to
improve the status of the species in its natural habitat to such a degree
that it can be delisted. However, by the time a species becomes eligible
for listing, its habitat is often destroyed or badly degraded, the
population is decimated, and its genetic diversity seriously eroded.
Additional delays in developing and implementing recovery plans further
imperil the species. In practice, recovery plans are often not developed
for years, if at all. Through 1991, 61% of the listed species had approved
recovery plans but, of the more than 200 species without recovery plans,
more than half had been listed for three or more years (GAO 1992). The
recovery of species under these circumstances is one of the greatest
challenges to the application of ecological science. In addition to being
delayed, recovery plans often have weak goals. A review of the 314
approved recovery plans for threatened and endangered species that were
approved by the U.S. Fish and Wildlife Service and the National Marine
Fisheries Service as of mid 1991, found that population goals were often
no higher than existing population densities at the time of listing (Tear
et al. 1993). More than half of the vertebrates would remain in serious
risk of extinction even if they met the population targets in their
recovery plans. In some cases, habitat destruction was so severe that the
recovery plans had little chance of success. The reviewers concluded that,
"Recovery plans all too often "manage for extinction"
rather than for survival" (Tear et al. 1993). The ultimate goal of
the Endangered Species Act is to restore populations so that they no
longer are threatened with extinction. When that state is reached, the Act
provides for delisting of the species.
III. The Role of Science in
The Endangered Species Act
Scientific information is needed for
implementing all of the processes specified in the Endangered Species Act.
The more high quality science is used, the more effectively and more
efficiently the Act can achieve the important goals society has asked it
to accomplish. A. Use of Science in the Listing Process Listing a species
as threatened or endangered is the first step in conferring legal
protection. It is the conclusion to a decision-making process that draws
heavily on ecological science, particularly for assessing the level of
risk to a species and developing priorities for listing. Species are
proposed for protection because they are thought to be in danger of
extinction or at risk of becoming endangered with extinction. For species
deserving protection, delaying the decision to provide protection and
recovery will bring most of these vulnerable species even closer to the
brink of extinction, restrict the options available for achieving
recovery, and increase the eventual cost of the recovery process.
Therefore, streamlining the listing process can increase the effectiveness
of the Act in achieving its goals and potentially reduce the total costs
of doing so. There is no scientific reason why listing, which is an
administrative decision based on the available information, should require
much time or agency resources. The uncertainty that may result from sparse
information is part of the risk that is evaluated during the listing
process. Adding independent peer review or other administrative processes
to the listing process would unnecessarily lengthen the time to make a
listing decision without providing any substantial benefits. The major
problem with the listing process has been its slowness, not inadequacy of
the quality of the listing decisions. 1. Which Biological Units Should be
Listed? In the language of the Act, a "species" is taken to
include any subspecies of fish or wildlife (including invertebrates such
as insects, crustaceans, and mollusks) or plant (including fungi). For
vertebrates, any distinct population segment of a species, that is one
with unique morphological features or genetic traits, qualifies as a
species. How distinct is distinct enough must be judged on a case-by-case
basis. The meaning of "species" in the language of the Act is,
therefore, somewhat imprecise, but the wording recognizes that a species
is made up of an assemblage of individuals that collectively express
genetic, morphological, and behavioral variation, and that this variation
is the basis of evolutionary change and adaptation. The scientific
justification for extending protection to distinct population segments of
species is that genetic diversity provides the raw material for adaptation
of a species to changing conditions. A wide geographic range decreases the
likelihood that a catastrophic event such as wildfire, disease, or alien
species introduction could wipe out an entire species. The capacity to
respond to environmental change through ecological and evolutionary
processes is enhanced by large population size, extended geographical
distribution (including spatial structure among its populations), and
intraspecific genetic diversity. Therefore, because loss of specific
population segments can contribute to the decline of a population and
increase the probability of its extinction, protection of population
segments is biologically appropriate. The National Marine Fisheries
Service has introduced the concept of an "evolutionarily significant
unit" to better define and identify distinct population segments. An
evolutionarily significant unit is a population that is reproductively
isolated from other populations of the same species, which therefore
represents an important part of the evolutionary history and future
evolutionary potential of the species. For example, the species of Pacific
salmon are subdivided into many distinct spawning runs that are
evolutionarily significant units of central importance for the future
survival and evolution of the species (Waples 1991). New species often
arise when genes from two species combine and the number of chromosomes is
increased, a process called polyploidy. Polyploidy has given rise to many
species of plants and some animals, including trout and salmon. Hybrid
populations may play unique ecological roles and may stimulate
evolutionary processes. For example, hybrid populations of plants
sometimes provide opportunities for increased speciation among herbivorous
insects (Bush 1975). The biological processes that produce these genetic
mixtures are natural components in the larger processes of speciation and
evolution. For these reasons, it is scientifically appropriate to protect
species of hybrid origin. 2. Science and Listing Priorities. Currently
more than 3,000 species are "Candidates" for listing under the
Endangered Species Act, including more than 2,000 vascular plants, 200
mammals, and 750 insects. This large number of candidate species greatly
exceeds the capacity of the Fish and Wildlife Service and National Marine
Fisheries Service to evaluate and propose species for listing as
threatened or endangered. In recent years, about 100 species have been
listed annually. The scarcity of resources available for listing species
requires agencies to make choices about how those resources can best be
allocated to meet the objectives of the Endangered Species Act. In the
1970s and 1980s, the FWS developed several different schemes for setting
priorities for listing species. These priority systems incorporated such
criteria as: magnitude and imminence of threat, availability of
information, taxonomic distinctness of the species, recovery potential,
and population status. The current scheme, adopted in 1983, establishes
priorities for listing based on three criteria: (1) Magnitude of threat,
(2) immediacy of threat, and (3) taxonomic status (the greater the
evolutionary distinctness of a taxon, the higher its priority). A fourth
criterion--recovery potential--is included in setting priorities for the
development of recovery plans. This system of priority-setting has the
advantage of being relatively simple. It uses information that is
available for most species, and employs criteria that can be evaluated
relatively objectively (Tobin 1990). However, it does not take full
advantage of ecological knowledge that could better guide limited
resources. From an ecological perspective, three attributes should be
considered in a determination of listing priorities: (a) Inclusive
benefits. Will the habitat managed on its behalf benefit other species,
especially species that are listed or are candidates for listing? Given
the limited resources available for endangered species protection, giving
high priority to species that serve as protective "umbrellas"
for other species makes good ecological sense. For example, the Florida
Scrub Jay (Aphelocoma coerulescens coerulescens) is restricted to scrub
oak habitats on the Florida peninsula. Many rare species of reptiles,
insects, and plants inhabit, and are restricted to, those scrub habitats.
Many of them benefit from the land that is managed for the protection of
the jay. Similarly, many but not all species requiring old-growth
temperate rain forest will benefit if sufficient spotted owl habitat is
protected. The umbrella species approach must be used carefully because
every acre of land or body of water will contain large numbers of species.
Thus, virtually any organism could be considered an umbrella species at
some scale. Moreover, an important fact about endangered species is that
they rarely have exactly the same requirements. Therefore, even when a
suitable umbrella species exists, the ecological needs of other community
members must also be considered. The most useful umbrella species are ones
whose habitats harbor numerous endemic, rare species. Thus, umbrella
species should be given priority for listing in proportion to the number
of other endemic, rare species that co-occur with them. (b) Ecological
role. Does the species play an especially important role in the ecosystem
in which it lives? Do other species depend on it for their survival? Will
its loss substantially alter the functioning of the ecosystem? Keystone
species--an organism whose impact on its community or ecosystem is large,
and disproportionately large relative to its abundance (Power and Mills
1995)--merit special attention in the listing process. Unfortunately,
determining which species are keystone and which are not is difficult
because a species' importance in an ecosystem is not necessarily
proportional to its size, abundance, or charisma. Tiny fig wasps and
African elephants are both keystone species. (c) Taxonomic distinctness.
How evolutionarily distinct is the taxon in question? On scientific
grounds, the more evolutionarily distinct an organism is, the higher
should be its priority for protection. All things being equal, therefore,
saving the sole surviving member of a genus may have a higher priority
than saving an imperiled species within a large genus that contains many
other species. Similarly, protecting full species would normally be given
a higher priority than protecting subspecies and populations (Vane-Wright,
Humphries, and Williams 1991). Species also have important scientific,
aesthetic, and social values, but, given the paucity of information about
most species, priorities are difficult to assign using those values.
Therefore, provisionally it seems scientifically reasonable to give high
priority to species immediately threatened with extinction, to umbrella
species, and to taxonomically unique species. Existing priorities for
listing also could be modified by including considerations of inclusive
benefits and ecological role. For example, among current high priority
species (species and monotypic genera facing high magnitude imminent
threats), those providing more inclusive benefits or playing more
important ecological roles should be given higher priority. B. The Use of
Science to Establish Recovery Priorities The immediate consequence of
listing a species under the Endangered Species Act is to trigger a series
of processes that can recover the species and enable it to be delisted.
Recovery is much more complex and difficult than listing, and development
of recovery plans usually requires the generation of substantial new
information in addition to the evaluation of existing information. 1.
Science and Critical Habitat Designation. Once a species is listed, the
Endangered Species Act requires the designation of "critical
habitat." Because loss of habitat is the cause of endangerment of
most species, designation and preservation of habitat is a vital part of
Endangered Species Act procedures. Because recovery is a long-term, not a
short-term process, and the goal of the Act is to preserve species in
perpetuity, enough habitat must be preserved to allow the species to
survive in the long term. But how long is long term and how much is
enough? The scientific procedure used to estimate the probability of
survival of a population for a specified period of time is known as
Population Viability Analysis, or PVA (Shaffer 1990). Although there is no
strict definition of what is or is not included, each PVA should include
an analysis of the best available information on the focal species. Most
PVA analyses combine data from field studies with simulation modeling of
the possible impacts of various extinction factors (Doak et al. 1994,
Murphy et al. 1990; Menges 1990; Stacey and Taper 1992). The details of a
PVA analysis depend on the characteristics of the focal species (Murphy et
al.1990). Species with low population densities and small geographic
ranges (most endangered large vertebrates, for example) and small
geographic ranges (many plants) require a PVA that includes analysis of
the genetic and demographic factors that affect small populations. Smaller
organisms, such as most threatened invertebrates, frequently are
restricted to a few habitat patches, but within those patches they often
have high population densities. For these species PVAs need to analyze
environmental uncertainty and the probability of local catastrophic
factors. PVAs for plants require different emphases than PVAs for animal
species because individual plants may survive for many years even if they
are not reproducing successfully (Schemske et al. 1994). A PVA for a
migratory species may also have to incorporate explicitly how its
populations are linked through migration and how its population dynamics
are influenced by processes operating at a landscape scale. A good PVA
addresses the issue of how long is long enough by attempting to answer the
following questions: Is the population viable in both the short term and
the long term? What factors are currently putting it at risk? How can
these risks be reduced or eliminated so that the population can both
survive and recover? There are no clear criteria for determining how long
is long enough, but in practice a minimum viable population (MVP) is
typically defined as one that has a 90% probability of persisting for 200
years. A PVA was performed on the Acorn Woodpecker (Melanerpes
formicivorus), a non-endangered bird that lives in small, isolated
populations in the oak woodlands of western United States and Mexico
(Stacey and Taper 1992). A simulation model showed that most of these
populations would become extinct within 20 years if they were totally
isolated from one another. However, with a small amount of migration among
populations, the model indicated that most of the populations would last
more than 1,000 years. Historical records indicate that local populations
of these woodpeckers have survived more than 70 years, suggesting that
migration must be important in maintaining them. Population viability can
seldom be assessed by focusing on a single patch of suitable habitat and
the organisms living in it. Most organisms live in islands of suitable
habitat, among which there is an exchange of individuals, embedded in a
larger landscape. Because the populations in the various patches are
linked by the movement of dispersing individuals, the fate of the
populations is interconnected. Studies of population viability of many
organisms will therefore need to consider the importance of factors that
link subpopulations. The whole set of populations of a species that are
linked through migration in a habitat mosaic is known as a "metapopulation."
The long-term survival of metapopulations can be strongly affected by the
spatial and temporal distribution of suitable and unsuitable habitat
patches. Populations living in high quality habitats (referred to as
"source" habitats) have birth rates greater than death rates;
the excess individuals may migrate into lower quality habitats
("sink" habitats) where birth rates are less than death rates.
The viability of metapopulations depends on the existence of sufficient
high quality habitats, but a large fraction of the individuals may live in
the sub-optimal habitats (Pulliam 1994). To determine the critical habitat
needs of such species requires identification of source and sink habitats,
which may be difficult. Not every rare and endangered species is patchily
distributed in a spatially structured habitat mosaic. Some live in just a
few continuous or in completely isolated habitats. Some have a
"core-satellite" structure in which one very large population
(the core) determines the population dynamics in the small (satellite)
populations. Nonetheless, because many species do depend on source and
sink habitats, every protection and recovery plan for species should
investigate the need to include (1) spatially distributed populations that
are linked through migration, and (2) special protection of the most
stable, high quality habitats. For some species, the designated critical
habitat may need to include more than habitat actually occupied by the
species. This is especially true in cases where the quality of critical
habitat is dependent on land use in the surrounding area (e.g., Noss 1983,
Turner et al. 1995). Although this is a general concern, the need for a
larger scale of focus in the designation of critical habitat is most
apparent for aquatic species. If the watershed that supplies river and
lake ecosystems is degraded, the critical habitat needed by the endangered
species may also be destroyed. The data available for most candidate
species will not allow a precise determination of MVP or critical habitat.
From a scientific standpoint, the resolution to this problem is to
designate interim critical habitat at the time a species is listed and to
designate long-term critical habitat as part of the recovery plan. A
monitoring and research program that generates information about the
requirements of the species needs to be established. Procedures should
allow for revisions of critical habitat designations if suggested by
additional information. The Endangered Species Act, although it focuses on
species as the objects of concern, clearly recognizes that preservation of
the ecosystems upon which endangered and threatened species depend is a
necessary component of the recovery process. This feature was written into
the Act because loss of habitat is by far the most important cause of
endangerment of species in the United States. A particular habitat type
may be lost by destruction or conversion to other habitat types unsuitable
for the species that live in it. A habitat may also be degraded by
pollutants without being otherwise altered. The fact that habitat
preservation is the most important element of most recovery plans creates
several possibilities for using scientific information in more
comprehensive ways. Because many species that depend upon a habitat that
has been greatly reduced in area or otherwise degraded are similarly
affected by losses of that habitat, a number of listed or candidate
species are likely to live in the same habitat. In a recent out-of- court
settlement, the United States Fish and Wildlife Service formalized a
commitment to emphasize multiple species listings and proposals that
address entire ecosystems (Jaffe 1993), a result that demonstrates the
appropriateness and legality of multispecies processes under the existing
Act. Managing for multiple species within a single management area focuses
efforts on recovery of threatened species while simultaneously directing
attention to broader issues of habitat quality and quantity. Multispecies
planning differs from ecosystem management because its focus is still on
species. Nonetheless, a multispecies approach to preservation plans
inevitably directs attention to habitats and ecosystems. Habitat-based
packages that combine the listing efforts for many species have the
potential to eliminate unnecessary duplication of efforts and to prevent
species from becoming threatened in the first place. Thus, a likely
consequence of more extensive use of a habitat approach is that the need
to invoke the Endangered Species Act will arise less frequently than it
does now. 2. Use of Science in Protection and Prohibition against Jeopardy
Section 7 of the Endangered Species Act provides immediate protection to a
species when it is listed as threatened or endangered. The analyses
leading to no jeopardy or jeopardy opinions, together with the search for
nonjeopardizing alternatives, offer considerable scope for the use of
ecological knowledge. Jeopardy opinions, as well as non-jeopardy opinions,
may become irrelevant unless they are regularly updated to reflect changed
circumstances and new information. Ideally, recovery plans should provide
tangible standards or yardsticks for judging whether particular federal
actions satisfy Section 7. Recovery teams could play a useful role in this
regard, by advising the Fish and Wildlife Service and National Marine
Fisheries Service with respect to particular consultations. The likelihood
that a species will become extinct does not increase uniformly as its
population declines. Rather, thresholds at which the probability of
extinction rises rapidly are the rule. The importance of thresholds needs
to be taken into consideration during evaluations of "incidental
take." A determination of the consequences of incidental take should
be based on the effect it would have on the process of restoring the
species to its safe minimum population density. Thus, if the damage from
incidental take was estimated to cause a 5% loss in the population size of
a listed species, the consequences of that additional mortality on the
likelihood of extinction could be shown explicitly through a population
viability analysis. Furthermore, because PVAs emphasize the principal
causes of a species' vulnerability to extinction, alternatives to the
proposed action, such as mitigation, could be considered and evaluated. In
the broadest sense, the implementation of the Endangered Species Act is a
process of risk assessment and risk management. Assessing risk of
extinction, which is the function of the listing process, is a purely
biological procedure. Any associated economic consequences that might
arise from designating an imperiled species as endangered or threatened
are not, and should not be, part of the risk assessment equation. However,
in the "risk management" phase which follows the listing of a
species, the Act appropriately permits the consideration of possible
economic costs and infringement of personal property rights in the
designation of critical habitat, in the determination of allowable harm to
the species (takings and jeopardy), and in the development and
implementation of recovery plans. Formal population viability analyses
could assist this process because a given level of probability of survival
for a specified time period might well be achieved in many different ways,
some of which would impose more restrictions on private land owners than
others. PVAs could identify those options that would achieve maximum
protection while reducing costs and lowering political controversy.
Science can play a valuable role in stimulating the consideration and
evaluation of a wide range of actions at the time a federal action is
contemplated. All too often formal consultations are limited to a
consideration of a small number of options that are proposed as ways of
avoiding harm to some listed species. Impacts of the options on other
species often are not considered, and options that might be better than
those being evaluated are rarely discussed. Broadening the range of
options being considered increases the up-front costs, but if superior
options are identified and eventually implemented, long-term costs may be
reduced substantially. Biologists in the agencies responsible for
implementing the Endangered Species Act generally try to use the best
scientific information and methods available. Failure to use the best
available information and methods is generally due to inadequate budgets
and overworked staff. Incorporating greater scientific rigor into the
recovery process will result in initially higher costs because better
methods for identifying species at risk, formal population viability
analysis, and adequate habitat restoration and recovery programs all
require greater investment. However, if the best available science is used
consistently, common patterns will emerge and species protection and
recovery will become more cost-effective. In other words, as experience is
gained, each new case can build upon the results of previous cases. Rather
than treating each new species to be protected as a totally novel
situation, more powerful general rules can be applied and the process
thereby simplified. The rapidly growing field of Conservation Biology,
with its own professional, scientific Society of Conservation Biology, is
already providing some of the needed information. Furthermore, the
development of general rules that are well-grounded in both experience and
theory, can be useful in predicting which kinds of species and
circumstances are likely to be sensitive to disturbance from human
activities and in evaluating acceptable alternatives to the proposed
actions. In many regions of the United States, particularly the West Coast
and the Southeast, threatened and endangered species occur on private
land, and the concurrence of landowners will be required to protect the
habitat of the species and to implement species recovery plans. This
situation generates a need for interdisciplinary studies by resource
economists and ecologists. The objectives of these studies should be the
development of models and field approaches for determining least-cost
solutions to habitat protection. Furthermore, the pathways to these
solutions should be "user-friendly" so that landowners can
identify with the process. As an example of this approach, Liu (1992)
developed a model for pine plantation management that shows the effects of
different tree harvesting patterns and rotation lengths on the population
size of Bachman's sparrow. This model shows how the real opportunity costs
of forgoing the most profitable management plan are related to the
probability of survival of Bachman's sparrow. 3. Use of Science in
Development and Implementation of Recovery Plans. When a species is
listed, the Endangered Species Act requires that a recovery plan be
developed. The ultimate goal of the recovery plan is to recover the
species in its natural habitat to such a degree that it can be delisted.
However, by the time a species becomes eligible for listing, its habitat
is often destroyed or badly degraded, the population is decimated, and its
genetic diversity seriously eroded. Therefore, scientific information is
especially needed for setting population goals, captive breeding and
release, and habitat protection and restoration. (a) Setting Goals for
Recovery. The first goal of a recovery plan is to stop the population
decline before the species is on the brink of extinction. If listing as an
endangered species was warranted, a recovery plan usually must aim for a
population size significantly greater than the size at the time of
listing. A good recovery plan for an endangered species typically has
three goals for achieving viable populations. First, it calls for the
establishment of multiple populations, distributed so that migration among
them is possible, so that a single catastrophic event cannot wipe out the
whole species. Second, it moves to stop known threats that guarantee the
continued decline and eventual extinction of the population. Third, it
plans for achieving annual population growth rates greater than zero,
which will increase the size of populations to levels where demographic
and normal environmental uncertainties are less threatening. Doing so
requires careful analysis of the habitat requirements of the species and
the distribution of suitable habitats in the landscape. Analyses to
determine long-term recovery goals and programs for attaining them are a
vital component of recovery plans. However, because their development may
require considerable time, short-term interim goals may be needed to
prevent the species from becoming extinct while long-term plans are being
developed. Interim population goals should be biologically attainable
during the first years of the recovery process. One exception to setting
larger recovery goals is if a species were naturally restricted to a very
small area. In such a case, it might be listed as endangered, but recovery
might require only removal of the threat it faces, in the restricted area.
General tentative guidelines for establishing viable population sizes are
available (e.g., Gilpin and Soul‚ 1987) but these target population
goals are no more than rough estimates and should not be viewed as
substitutes for a more thorough analysis. Interim populations goals need
to be flexible and readily adjustable. For example, an appropriate goal
over a three-year period for a rapidly reproducing species might be the
establishment of three semi-isolated populations with a combined
population size greater than three times the original population size at
the time of listing. For species with low reproductive rates, an increase
in the size of the population of that magnitude within a few years may not
be possible. Although interim goals are necessary, population viability
analyses should begin immediately so that long-term population goals can
be established and the most important factors threatening the species can
be identified in a timely manner. It is always tempting to set as a
recovery goal a population of a specific size and spatial distribution.
For many species, however, a goal of a relatively constant population is
biologically unrealistic and probably intrinsically undesirable. Many
species live in unstable, fluctuating environments, and their populations
have historically fluctuated together with the states of their
environments. For example, many species depend upon habitats that are
maintained by periodic fires, droughts, or floods. Populations of such
species inevitably fluctuate greatly in space and time. Realistic
management goals must reflect this biological reality. For example, the
1986 recovery plan for the Snail Kite (Rostrhamus sociabilis) in the
Florida Everglades sets an interim population goal for reclassification
from endangered to threatened of an "annual average of 650 birds for
a ten-year period with annual population declines of less than 10% of the
average." However, kite numbers vary, and have probably always
varied, considerably according to surface water conditions, which change
dramatically along with drought cycles in southern Florida. Achieving a
population having the stability outlined in the interim population goal is
probably unattainable. Also, attempting to achieve great population
stability might well lead to management interventions that in the long
term reduce the quality of kite habitat and, hence, the long-term
viability of the population. However, it is generally useful to establish
critical minimum population sizes below which extinction probabilities
become unacceptably high even if they are sustained for only short time
periods. (b) Captive-breeding and Translocation. Reintroduction of
captive- bred individuals and translocation of individuals between
populations are often components of recovery plans. However, captive
breeding programs are expensive, can save only one species at a time, and
can be used only rarely because available facilities are limited. Also,
because unexpected undesirable consequences may arise, captive propagation
programs are risky. Deleterious genes may arise in captivity, or
individuals released in areas other than the ones from which they or their
parents were taken may not be adapted to the environments in which they
are released. Diseases may be carried by the reintroduced individuals.
Behavioral traits may develop in captivity that prevent individuals from
functioning appropriately in nature. For these reasons, careful attention
must be given to the sources of individuals for release to the wild and
their treatment in captivity. Similar considerations apply to
introductions of plants propagated in botanical gardens and other
artificial environments. There is also a danger that wild populations may
be depleted to obtain individuals for captive breeding programs, although
in special instances, such as occurred in the case of the California
Condor in the 1980s, capture of all remaining individuals in the wild
population may be warranted. Captive breeding programs may draw attention
away from the need to protect and restore habitats for the focal species.
Successful species recovery plans ultimately depend on adequate amounts of
protected habitat. Captive-release or translocation programs of native
populations, although important, cannot substitute for the failure to
protect or restore natural habitat (Povilitis 1990). The danger is
illustrated by the Gila topminnow, which was reclassified from endangered
to threatened because artificial habitats were successfully restocked with
captive-bred fish. However, the natural habitat continued to degrade from
the effects of alien mosquitofish and agricultural water withdrawals
(Simons et al.1989). The continuing loss of the fish's natural habitat
makes its survival in artificial pools increasingly improbable. (c)
Habitat Protection and Restoration. Often the best approach for restoring
habitat is to control the source of the degradation and let nature take
its course. Unfortunately, habitats are often very badly degraded or too
small to contain adequate heterogeneity and natural disturbance regimes.
In those situations, active management is needed to restore and maintain
the habitat. Habitat restoration and ecological management are critically
important to the species recovery process. Methods to restore and manage
habitats are not yet well-developed, but the field of Restoration Ecology
is growing rapidly (Jordan, Gilpin, and Aber 1987; MacMahon and Jordan
1994). Its practitioners increasingly should be able to provide insights
and guidance for restoration efforts in a variety of habitats. Critical
components in the development of a recovery plan for a listed species are
determination of the current extent of its suitable habitat, assessment of
the quality of the remaining habitat, and establishment of priorities for
the areas to be targeted for restoration efforts. Restoration efforts can
also be designed to test hypotheses about how the ecological community in
question functions and the roles of the various species that might be
reintroduced as part of the restoration project. Ideally, several
different restoration projects should be initiated in different patches of
a given habitat so that more than one hypothesis about the functioning of
the community can be tested. Such a procedure would increase the
probability that the results of specific restoration projects are
generalizable to other habitats, while increasing the speed of restoration
of the habitat in question by identifying more promising restoration
techniques. C. Delisting, the Ultimate Goal of the Endangered Species Act
Delisting is the ultimate objective of the Act. Measures of progress
toward this goal include prevention of extinction and slowing the rate of
population decline. The criteria for delisting should be established early
in the recovery process, and they should be based on sound biological
information. As discussed previously, delisting criteria should be
consistent with natural fluctuations in the habitats supporting a species.
However, results obtained as recovery was underway may require
modifications in the original criteria as better information about habitat
requirements and population dynamics of the species become available.
IV. Conclusions
Protection is not afforded to species and
their habitats under the Endangered Species Act until species are already
threatened with extinction. By that time, both the range of a species and
its total population size are likely to have been seriously reduced.
Recovery under these circumstances is likely to require major habitat
restoration efforts and, possibly, captive propagation. These activities
are more expensive and are less likely to be successful, the later in the
decline of the population they are initiated. Therefore, the goals of the
Endangered Species Act are more likely to be achieved, and to be realized
at lower total cost, if preservation of biological diversity were
approached in a more proactive manner. The most important elements of a
proactive approach would be to identify habitats and biological
communities that are being seriously reduced in area or are being
otherwise degraded and then to establish policies that prevent further
losses of those habitats and restore degraded parts of them. Such an
approach could not replace a species- by-species analysis because not all
species are threatened by habitat loss and threatened species require
different habitat types. Nonetheless, a habitat-based, proactive approach
should greatly reduce the number of species that would need to be
considered for listing. In addition, a proactive approach, by identifying
habitats experiencing or likely to experience serious losses would allow
federal agencies to initiate preservation plans while more options are
available than will be present at such time when particular species would
become candidates for listing. Habitat-and ecosystem-level planning can be
accomplished under the existing Endangered Species Act, particularly
through the use of critical habitat designations for already listed
'umbrella species." For both scientific and economic reasons, such
proactive planning needs to be greatly increased. The establishment of the
National Biological Service is an important step in developing the data
needed for proactive, habitat and ecosystem level planning. However, if
the protection of habitats and ecosystems is to become an important means
for conserving biological diversity, some important questions need to be
addressed. Ecosystems are not closed systems; they are dependent on
outside conditions. Ecosystems and habitats can be recognized at many
scales. Aquatic ecosystems may range in size and complexity from small
ponds to the Great Lakes. Determining the most appropriate scales for
protecting them will require considerable information and complex
biological judgments. New legislation for ecosystem-level protection,
designed to complement and strengthen current legislation, could greatly
assist protecting the nation's renewable natural resources, including its
rich biological diversity. An ecosystem approach could help to reverse the
slide towards extinction by preventing habitat degradation. The Endangered
Species Act would then function as the safety net for those species whose
survival cannot be guaranteed within the protected ecosystems. |