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OCR for page 57
Chapter 4
The Role of Habitat Conservation and
Recovery Planning
THE IMPORTANCE OF HABITAT
Habitat is the physical and biological setting in which organisms live and in which the other
components of the environment are encountered (Iones, 1987; Krebs, 1985~. The concept of habitat is
critical to modern ecology and was adopted and promulgated in some of the earliest treatises and texts
(ETton, 1927; Clements and Shelford, 1939~; habitat is a basic requirement of all living organisms
(e.g., McNaughton, 1989~. Habitat is one of the four components of a species' environment, along
with climate variables, nutrients, and other interacting organisms (Andrewartha and Birch, 1954~. The
fact that habitat serves a multitude of organisms is critical to understanding its full role in the
Endangered Species Act. Many species have not been classified, nor their status determined. Our
knowledge of species is too limited, and the species deserving of endangered or threatener} status too
numerous, to list all that might merit it in a time frame adequate to protect them. The number of
unclassified living species is thought to be from two to ten times the number that have been identified
and named (Wilson, 1992~. Although this gap in knowledge is greatest in the tropics, invertebrates are
also incompletely described in temperate habitats, particularly for soil organisms and many marine
groups. Even among named species in the United States, genetic diversity of subspecies and of
vertebrate population segments is poorly understood, except for relatively few vertebrates that have
received special attention because they are commercially or recreationally important. Prospects are
scant for a significant, near-term change in this information gap, because the task is so immense, ant!
there are few specialists for many plant or invertebrate taxa. Therefore, broad, ecosystem-basec}
conservation measures that depend neither on taxonomic knowlecige nor on the determination of listing
status of individual species are also needed to prevent species extinction (see Chapter 101.
Fortunately, the distribution of habitats on which species diversity depends is somewhat better
understood. In California, for example, reliable inventories document the loss of habitat and the extent
of many valuable remnants, including coastal and intend wetlands, native coastal dunes, coastal sage
scrub, oak woodlands, vernal pools, and free-flowing rivers (Jensen et al., 1993~. Many endangered
species are also found in California, as the Endangered Species List (50 CFR 17. ~ ~ & 17.12) shows.
The relationship, nationwide, between vanishing habitats and vanishing species is well documented (see
Chapter 21.
Based on studies of the relationship between habitat area and several groups of organisms, a
simple and fairly general ecological relationship has emerged: species diversity is positively correlates}
with habitat area (McArthur and Wilson, 1967; Pianka, 1978~. The relationship is S = CAZ; where S
is the number of species, A is the area of the habitat, and C is an empirically cletermined multiplier that
varies from place to place and among taxa. The exponent z varies according to topographic diversity
and isolation of the habitat; z is usually larger for islands (aroun(10.3) than for mainland habitats (often
less than 0.2~. A corollary of this relationship is that if habitat is substantially reduced in area or
degraded, species will be lost. The loss is not linear; a loss of 90% of the habitat results in the
estimated loss of 30%-60% of the dependent species (Groombridge, 1992~. The species loss might be
even greater than 30%-60% for at least three reasons. First, we lack sufficient taxonomic and
57
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58
Science and the Endangererl Species Act
ecological understanding of many taxa that might have clemancis on habitat area quite different from
those of the more intensively studied taxa. Also, lack of knowlecige about a taxon can lead to an
incorrect evaluation of the species-area relationship for it, because it can react to misidentification of
species. Second, many species-area relations were developed for nonmigrant species, tropical species,
and true island populations conditions that strictly apply to few North American taxa. Third, habitat
can be altered in many ways, and the effects of most of these alterations on species numbers have not
been studied.
Despite uncertainties in the actual mathematical relationship between habitat size ant! the number
of species in that habitat, there is no disagreement in the ecological literature about one fundamental
relationship: sufficient loss of habitat will leacl to species extinction (see Chapter 2~. Ancl habitat
protection is a prerequisite for conservation of biological diversity. Habitat protection is essential not
only to protect those relatively few species whose endangerment is established, it is also in essence a
pre-emptive approach to species conservation that can help to avoid triggering the provisions of the
Endangered Species Act.
Loss of habitat is a major factor in species extinctions when the cause of extinction is known.
Groombridge (1992) proviclect a table showing that for animals with known causes of extinction,
hunting (mostly unregulated) caused extirpation of 23 %, introduced animals caused 39%, and habitat
loss accounted for the loss of 36%. Habitat loss has been more important as a recent cause of
extinction of terrestrial than marine species to date and probably accounts for more than 36% of the
extinctions where the cause is unknown, because extirpation clue to unregulated hunting is easily
clocumented.
Habitat loss places additional pressures on endangered species management because where the
amount of habitat available is limited, protection or maintenance of the present condition of a habitat
for one species can adversely affect another (see Chapter 6~. For example, boundaries or edges
between different habitat types (gaps or openings) favor some wilt/flowers and other desirable plants
(Whitford, 1949; Gilbert, 1980), but large, unbroken tracts of habitat favor other species. When the
amount of habitat available is limite~i, the design of optimal combinations of mosaics of distinct habitats
across landscapes becomes a major challenge to managers.
THE ROLE OF HABITAT CONSERVATION UNDER THE ESA
The role of conserving habitat for endangered species has been recognized since the first federal
endangered species legislation. For example, the Endangered Species Preservation Act of 1966 (Pip.
89-699), stated, "It is . . . the policy of Congress that the Secretary of Interior, the Secretary of
Agriculture, and the Secretary of Defense . . . shall preserve the habitats of such threatened species on
lands under their jurisdiction" (Section label. Over time, as our knowledge of species requirements has
grown, the legislation has evolved from the regulation of harvest and trade in species to the protection
of habitat. The stated purposes of the current ESA are to conserve endangered species "and the
ecosystems on which they depend" (16 U.S.C. 1531), a clear mandate linking successful conservation
of species to the habitats that they require. This linkage is entirely appropriate scientifically.
The ESA provides throughout for the identification and protection of habitat. The first statutory
consideration for the listing of species as threatened or endangered is "the present or threatened
destruction, modification or curtailment of its habitat or range" (§1533~. Section 4 of the act further
requires the designation of a species' "critical habitat" concurrently with the listing of a species, unless
earlier listing is "essential to the conservation" of the species §1533(b)~6~(C)~) or unless the
designation of critical habitat is not "prudent" or "determinable" (§ 1533(a)~31~. Critical habitat
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The Role of Habitat Conservation and Recovery Planning
designations are, "to the maximum extent practicable," to be accompanied by "a brief description and
evaluation of those activities (whether private or public) which, in the opinion of the Secretary, if
undertaken may adversely modify such habitat, or may be affected by such designation"
(§1533(b)~6~. Critical habitat is to be designated "on the basis of the best scientific data available ant!
after taking into consideration the economic impact, and any other relevant impact, of specifying any
particular area as critical habitat" (§1533(a)~31. (Critical habitat designation is not mandated for the
species listed before 197S, when these provisions were added. To date, critical habitat has been
designated for less than 20% of all species listed in the Uniter! States. Furthermore, the ESA provides
for exclusion of areas from critical habitat if it is determined that "the benefits of such exclusion
outweigh the benefits of specifying such area," unless failure to designate the area "will result in the
extinction of the species concerned" (§1533(b)~211.
59
Section 7 requires federal agencies to consult with the Fish and Wildlife Service (FWS) and the
National Marine Fisheries Service (NMFS) to ensure that fecleral actions are not likely to jeopardize the
continued existence of listed species or result in "the destruction or adverse mollification" of their
critical habitat (§15361. Habitat mollification gives rise to the vast majority of these consultations,
nearly all of which are resolved informally or with mollifications that allow projects to proceed as
planned.
Sections 9 and 10 of the act have extencled the review of habitat modification to nonfederal,
private development. (However, recent court decisions have left uncertain the validity of FWS
regulations that state that habitat mollification constitutes "take.") Section 9 prohibits "take" of a listed
species, a term described elsewhere in the act as, among other things, "harm" to a species. Early FWS
regulations described this harm to include "significant habitat modification or clegradation" that "kills or
injures wildlife" (50 CFR 17.3~. The act's application to habitat modification by private parties led to
the development of early conservation plans in California, a process endorsed by the Congress in 1982
with the additions to Section 10. Section 10 (a) currently requires "habitat conservation plans" of
private parties seeking to secure an "inciciental take" permit (unintentional take) for listed species
(§ 1539(a)~2~.
One exception to the habitat conservation planning requirements of Sections 9 and 10 is worth
.
.
noting. Although Section 7 constrains federal agencies from jeopardizing Plant and animal species. no
~. · , · _ _1
_ J ~ ~ ~ · ~
such constraints are imposed on private parties for the incidental taking of listed plants. Private parties
are forbidden only from "removing" or "maliciously" damaging or destroying endangered plants found
either on federal lands or under the protection of state law (§1538(a)~211. However, plants are covered
by habitat conservation plans in that the Section 10(a) permit requires a consultation under the Section 7
requirements.
Recovery planning under Section 4 of the act is likewise keyed to habitat protection. Each
recovery plan is to include "site-specific management actions as may be necessary to achieve the plan's
goal for the conservation and survival of the species" (§1533(i)~11(B)~. Because most species are
endangered due to loss or degradation of habitat, site-specific actions should include identification,
restoration, and management of habitat.
lithe Supreme Court has agreed to review Babbitt versus Sweet Home Chapter of Communities for a Great
Oregon. The case focuses on Fish and Wildlife Service (FWS) regulations concerning the act's prohibition
An,
against taking an endangered species, in this case, the northern spotted owl. Take is defined in the ESA to include
harm, and FWS has defined harm to include significant habitat modification that adversely affects an endangered
species. The U.S. Court of Appeals for the District of Columbia ruled in a split decision that "the Service's
definition of 'harm' was not clearly authorized by Congress nor a reasonable interpretation' of the statute" (1994
U.S. App. LEXIS 4341).
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60
Science and the Endangered Species Act
Habitat acquisition for endangered! species has also been a part of the federal program from its
beginnings. Later amendments to the ESA have augmented the authority and funding for this effort,
but acquisition has not kept and cannot keep pace with the number and size of the affected habitats or
the modification ant! degradation that they face.
In summary, habitat protection has always been an important component of endangered species
programs. As our experience with endangerment and recovery has increased, habitat has become the
central ingredient, and the ESA, in emphasizing habitat, reflects the current understanding of the
crucial biological role habitat plays for species.
CRITICAL HABITAT AND FEDERAL ACTIVITIES
Section 7 imposes a special requirement on federal agencies to ensure that their activities are "not
likely to . . . result in the destruction or adverse modification of habitat of flistecI] species which is
determined by the Secretary, after consulting as appropriate with affected States, to be critical . . .".
Critical habitat is a valict biological concept. The requirement of Section 7 corresponds to the
understanding of conservation biology that certain habitat is essential for species survival. Habitat
critical to species can be identified from the knowledge of species and ecosystems as objectively and
scientifically as a species can be identified for listing. However, as is the case with listing decisions on
many rare species, detailecl information needed to (lesignate critical habitat might be lacking. Simple
occurrence of a species within a habitat floes not necessarily mean that the habitat is required by the
species (Van Home, 1983) or that the amount and quality of habitat might be considered} "critical."
But that a species is absent from a given habitat floes not mean that the habitat is not critical to the
persistence of the species (see Chapter 51. Identification of the relationship of a species to habitat and
the determination of what is critical to the long-term survival of that species are high priorities for long-
term conservation. The complexity of designating critical habitat will vary by species, but designation
should be possible in many cases. Mechanisms exist to uncouple critical habitat designations from
listing when they need additional investigation and would! otherwise cause delay. Mechanisms also
exist to withhold these designations where they are not "determinable" or otherwise "prudent." That
nearly 80% of all species listen! do not have critical habitat designations is a cause for concern.
Survival Habitat
The question has been raised whether critical habitat should be cletermined at the time of listing
or whether it should be deferred to the time of recovery planning. The advantages of early designation
include the provision of some "early warning" to all parties, and in particular, the affected federal
agencies, that such areas are to be treated with particular caution. Designated habitat is protected by a
more objective standard ("no adverse mollification") than that provided for threats to species ("no
likelihood of jeopardy") in that adverse habitat modifications are more amenable to objective
measurement and quantification than are the many factors that might contribute to jeopardizing the
survival of a species. The standard of habitat protection provides an important point of focus for those
outside of government, including the scientific community, to help protect areas at least until recovery
plans are developed that will clarify the needs of endangered species and provide more fully for their
recovery. Importantly, critical habitat designation can be beneficial to other listed and nonlisted species
living in the clesignated area, especially for those species for which satisfactory long-term recovery
plans have not been implemented.
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The Role of Habitat Conservation and Recovery Planning
61
The committee recognizes that 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. Because critical habitat plays such an important biological role in endangered
species survival, we believe that some core amount of essential habitat should be designated at the time
of listing and should be identified without reference to economic impact. We recognize, however, that
economic review may need to remain linked to critical habitat determination in the ESA, and that
cietermination of areas essential to the recovery of a species, inclucling areas not currently occupied by
that species, can be especially complex. Hence, we recommence designation of survival habitat for
endangered species as follows:
i. Survival habitat would be designates! at the time of listing, unless insufficient information
were available or harm to the species would occur. For this purpose, survival habitat would mean that
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 larger2. Survival habitat would receive the full
protection that the Endangered Species Act accords to critical habitat, and the adverse modification
standard of Section 7 (a)~2) would apply. No economic evaluation would be conducted. The purpose
of this requirement is to preserve scientific and management options until recovery plans are in place
and effective.
2. 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. This
underscores the emergency and temporary nature of survival habitat. It is intended to be a way of
avoiding delays and providing immediate protection while a more comprehensive evaluation of habitat
requirements is performed, not as a substitute for critical habitat designation. Expedited review and
designation of survival habitat should be maple for each currently listed species whose critical habitat
has not yet been determined, unless recovery planning, including critical habitat designation, is
expected within the period required for survival habitat designation.
3. Subsequent recovery planning wouIc! include designation of critical habitat as currently
defined in the ESA (inclucling economic evaluation) to include areas necessary for species recovery.
Because in our recommendation essential survival habitat is identified 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. To avoid
harm that indefinite delays in designating critical habitat and formulating recovery plans might cause to
economic interests and to the endangered species itself, the implementation of this recommendation
needs to include ways of preventing those delays from occurring.
PRIVATE ACTIVITIES AND HABITAT CONSERVATION PLANNING
Endangered species are found across North America, and slightly more than 59 % of lancl in the
United States is privately owned (about ~ % is uncler state and local ownership and about 33 % is
federally owned (NRC, 1993~. Clearly, a program that targets only the portion of the United States
2 We do not specify a precise time, because the length of survival time expected should be based on
knowledge of the species' biology, including its generation time.
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62
Science and the Endangered Species Act
that is under federal control will not prevent species extinction. Habitat conservation planning under
Section 10 and, more recently, Section 4(cI) has addressed species protection on private lands. Two
examples of habitat conservation planning are described below.
HABITAT-CONSERVATION PLANS
In Section 7 of the ESA, Congress offered relief from Section 9 prohibitions against taking
endangered species where the government's actions were "not likely to jeopardize the continued
existence of any endangered! or threatened species." Similar relief was not available to nonfederal
parties when federal permits were not required for development or other activities. In its 1982
amendments to the ESA, Congress provided nonfederal parties the possibility of obtaining legal
exemption from Section 9 prohibitions against take of endangered species (and, by regulation, of
threatened species). It amenclect the ESA to provide private nonfederal parties "incidental take" permits
under Section 10(a), if a habitat conservation plan (HCP) is submitted that, when implemented, "will,
to the maximum extent practicable, minimize and mitigate the impacts of such taking" ant} "not
appreciably reduce the likelihood of survival and recovery of the species in the wild" (16 U.S.C.
1539(a)~21(A)~.
Congress also intended to provide a framework that would encourage creative partnerships
between the private sector and local, state, and federal agencies in the protection of endangered} species
and habitat conservation. The legislators pointed to the mocle! of the San Bruno Mountain HCP3,
cleveloped by private lanclowners and local, state, and federal government agencies to conserve the
endangered! mission blue butterfly (Plebejus icarioides missionensis) and several co-occurring species in
coastal California. Although it focused on listed} ant! candidate species, the HCP addressed the San
Bruno Mountain ecosystem as a whole, including its diversity of species and habitats. The plan
included protection of open space ant! habitat diversity; management, including control of exotic
species and habitat restoration; protection of sensitive species cluring project construction; funding of
plan activities; and assurances to the private sector that new requirements would not be imposed after
the plan was accepted (Thornton, 19911. Most of the grassland habitat of the butterfly was protected,
and its population more than a decade later is as large as it was before the plan was implemented.
The mocle} had its second test in southern California, where the threatened CoachelIa Valley
fringe-toed lizarc} (Uma inornata) survived in remnant sand-dune habitats, at risk from suburban
expansion around Palm Springs. Challenged to preserve both dune habitat and distant montane sources
of sanct, FWS ultimately agreed to a reserve system of nearly 17,000 acres. However, this habitat
constitutes barely 10% of the occupiable habitat that existed at the time the HCP was initiated, and little
is known even now about what characteristics of the lizard's biology cause its dramatic population
fluctuations and put it at risk of extinction (BeatIey, 1994~.
These plans have had few imitators. Several promising regional HCPs have collapsed before
completion. Two of the more notable ones are the North Key Largo (Floricla) HCP, designed to
conserve the American crocodile (Crocodylus acustus), the Key Largo woodrat (Neotoma fitoridana
smalls), the Key Largo cottonmouse (Peromyscus gossypinus allapaticoZa), and other species; ancl, very
recently, the Balcones Canyoniancis HCP (near Austin, Texas), which focuses} on the black-capped
vireo (Vireo antricapillus) and the golclen-cheeked warbler (Dend~roica chrysoparia) among other
species and their habitats.
.
3H.R. Rep. No. 835, 97th. Congress, 2nd session 31, reprinted in 1982 U.S. Code Congressional and
Administrative News 2807, 2831.
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The Role of Habitat Conservation and Recovery Planning
Although FWS provides detailed guiclelines on administrative procedures for developing HCPs
(FWS, 1990; 1994), its directives in the application of biological data to plan development are very
sparse. The guidelines state that on request, FWS will indicate whether the biological data are
adequate to proceed with the other elements of this process. If desired, FWS will recommend the
number, type, scope, and general (1esign of studies needed to provide acceptable data to develop the
conservation plan. The FWS, however, has had remarkably few opportunities to exercise this offer,
because completed HCPs have been so few.4
Critics have argued that HCPs demand inordinate amounts of time, human resources, and
money, and they should be avoicled if possible (e.g., Mann and Plummer, 19951. Consultants
encourage private landowners to use any fecleral "hook" (i.e., relationship to some fecleral activity)
possible to avail themselves of the more expeditious Section 7 consultation process. Reasons for the
limited number of completer! HCPs are myriad, but at the very least, increased funcling is necessary to
upgrade the active role of FWS in the process. Furthermore, agency staff need the biological
guidelines that FWS offers to those who seek permits under Section lO(a). Appropriate guidelines
should be developed to assist planners in applying biological data to habitat-conservation planning.
They should include much of the agenda discussed in this report under recovery planning, as well as
elements from California's Natural Communities Conservation Plan describer! below. Finally, they
should attempt to resolve dilemmas that might arise if the need for ecosystem protection were to
conflict with the legal requirement of protection of individual species; in other words, an ecosystem
should not fad! to receive protection because of the needs of a single species. Wherever possible, HCPs
should be regional in scope and should serve multiple species across multiple habitat types. Mode}
programs are in process concerning the scrub community of Brevarci County, Florida and the southern
San loaquin Valley of southern California.
At a minimum, guidance should be offered in (~) development of explicit reserve design and
management goals and objectives, (2) identification of techniques and data needed to perform
population-viability analysis or equivalent demographic or metapopulation modeling efforts to assess
likelihoods of persistence of target species under alternative planning options, (3) description of
management options ant! (liscussion of how ongoing research and monitoring activities will be used to
adjust management in response to changes in population sizes and environmental variables, (4)
application of risk analyses in consideration of plan alternatives, and (5) description of how these
exercises should be applier] in the land-use planning process. Guidelines thus should describe a discrete
scientific program for HCPs that will be specific, efficient, and cost-effective (although it will usually
be impossible to make HCPs inexpensive).
63
RECOVERY PLANNING
The ultimate goal of the ESA is to recover threatened and endangered species. Recovery is
described as "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" (FWS, 19921. The 1978 amendments to the act first required that, following species listing, a
recovery plan be developed (§1533(f)~. Faced with delays in this part of the planning process and with
plans too vague to provide meaningful guidance, Congress has increased funding and provided more
detailed requirements for the contents of these plans (§ 1533f(1~(B)~. Despite this increased attention,
4From 1982 to July 1994, the FWS issued 33 incidental take permits and 12 permit amendments, but many of
those were very small projects rather than full-scale HCPs. Approximately 130 HCPs and permit applications are
now in various stages of development (FWS, 1994), most of them small in scope as well.
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Science and the Endangered Species Act
recovery plans are developed too slowly. There appear to be legitimate concerns about the adequacy of
their objectives and commitments to implement them. Those that involve species of little public
interest often sit unimplementecl for long periods, especially if they would be expensive to implement
(Tear et al., 1993~.
The backlog in recovery planning is significant because it is large, and because nearly everything
else in the act can be seen as a preliminary measure (e.g., listing) or as protecting the options for
recovery plans (e.g., critical habitat designation or consultation). In 198S, more than 10 years after
recovery plan requirements were first added to the statute, only 56% of listed species had recovery
plans approvecl, with another 18% in preparation. In 1992, some 61% of species had approved plans,
but by the following year the percentage hac! dropped to 53 %, a figure attributable to recent accelerated
listing actions. As of March 31 1995, resource agencies had approver! 411 plans covering 513 species,
54% of the 956 U.S. species listed at that time.
A FWS report to Congress (FWS, 1992)-the most recent data available to the
committee evaluated recovery progress as of September 30, 1992 based on the percentage of tasks
accomplished for downtisting, clelisting, or maintaining current populations for the foreseeable future.
Managers hacT attainer} greater than 50% of their recovery objectives for only 68 species, while 544
species (77 % of listed species, including all recently listed species) hac} less than 25 % of their recovery
tasks completed. However, the report noted that 201 species, 28% of the total, were stable and 69
species (10%) were improving.
A review of 314 recovery plans for threatened and endangered species as of 1991 (Tear et al.,
1993) concluded that
· Only about 17% of the plans contained population-size clata;
· Nearly one-thirc! of the plans with population data set recovery goals at or below the
population size believecl to exist at the time of listing; and
· Sixty percent of the vertebrates would remain at imminent risk of extinction with about a 20%
probability of extinction within 20 years or 10 generations, whichever is longer, even if every
population target were met.
In the recovery planning guidelines, recovery planners are asked to adhere to an explicit format
that includes (1) an introduction that describes pertinent ecological, genetic, and other information
related to the biology of the listed species and threats to it; (2) a recovery objective and criteria to meet
the objective; (3) an implementation schedule, including priorities of tasks and cost estimates; and (4)
an appendix identifying appropriate reviews of the plan ant! peripheral but pertinent documents or
communications. Recovery plan tasks 1 ant! 4 are by and large straightforward; unfortunately, tasks 2
and 3 are not, for different reasons.
The guidelines correctly observe that the quantification of "recovery criteria calls for creative
thought ant! cleveloping the criteria may require educated guesswork." Nonetheless, they demand
"concise and measurable recovery criteria" that will serve as "the central pillar of the recovery plan."
Population viability analysis is the cornerstone, the obligatory too! by which recovery objectives and
criteria are identified. Yet the demographic and genetic data necessary to fuel such analyses are
lacking for virtually all species for which recovery plans exist, and likewise for those in and awaiting
entry into the recovery-planning process.
In the absence of adequate data, "educated guesswork" has anti will continued to rule the
clevelopment of the "central pillar" of recovery plans. Moreover, few scientists agree on the data and
analyses that are required to produce a reliable population viability analysis for conservation planning
purposes. What most will agree is that many obligatory elements, such as variance in reproductive
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The Role of Habitat Conservation and Recovery Planning
success, are difficult to quantify and that the time-series data necessary to reduce the confidence
intervals around projections from population viability analyses demand long-term and expensive field
research. In essence, even to set objectives and criteria for recovery in a scientifically defensible
manner (much less to carry them out) will demand resources well beyond those currently available.
Nevertheless, many analytical tools that were unavailable to planners in the past now could be used to
add greater scientific rigor to recovery plans (see also Chapter 7~. However, the recovery guidelines
offer no explicit schedule or outline for bringing data to bear in setting recovery objectives or criteria.
The committee believes that FWS should convene a working group to develop explicit guidelines for
the application of data to the construction of recovery objectives and criteria, with particular emphasis
on the estimation of risks and the rational establishment of risk criteria.
Planners would receive general guidance covering at least the following topics:
1. A habitat-basecl, in situ approach to recovery that puts ex situ actions (e.g., captive rearing)
65
in their appropriate context.
2. A logical hierarchical approach to the analysis of available data on the species and its habitats
and to the acquisition of additional information on the species of concern and the habitats that support
it, including predictions from ecological theory and population (lynamics models and inferences drawn
from related species.
3. Guidance for the application of population viability analysis in conservation planning that
clearly identifies in planning prescriptions the inherent uncertainty that accompanies such demographic
modeling exercises.
4. An outline that describes in detail future research needs and how that research when
completer! will contribute to species ant} habitat management.
5. An effective monitoring scheme that relates census information to the physical and biotic
factors likely to affect population dynamics.
Because prioritizing activities is necessary but clifficult, and because estimating cost would be
helpful but nearly impossible for typical recovery teams to carry out, the committee recommends that
the prioritization and estimation of costs currently called for in recovery planning be reviewed.
Recovery planning remains han(licappe(1 by delays in implementation, the scientific validity of
objectives, and the uncertainty of application to other fecieral activities. To be scientifically credible
and to increase their likelihood of being successful, recovery plans should consider at least the
following questions.
How much of a species' historic range should be protected to ensure recovery or prevent
extinction?
Are there critical aspects of a species' life history or ecological and genetic requirements that
must be known to successfully implement a recovery plan? Are they known?
What is known about the species' use of and need for corridors among its various populations?
To what degree is a focus on a single species likely to be as successful as an approach that
includes the needs of other species in the area, or an ecosystem approach?
A final desired feature is that recovery plans reflecting the best judgment of science from
decisions made before listing through consultation and habitat planning bear some relationship to
decisions affecting the future of the species. We recommend, therefore, that all recovery planning
inclucle an element of "recovery plan guidance,'' particularly with regard to activities anticipated to be
reviewed under sections 7, 9, and 10 of the ESA. To the extent feasible, 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, ant} activities that require case-by-case evaluation. The
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Science and the Entlangered Species Act
guidance should also specify criteria for use in preparing habitat management plans by persons seeking
authorization for activities under Section 10 of the ESA and for the planning of federal agencies in
furtherance of their Section 7 responsibilities. These measures are fundamental to many recovery
efforts.
The real issue is that no recovery plan, however good it might be, will help prevent extinction or
promote recovery if it is not implemented expeditiously. Incleed, the failure to implement a recovery
plan quickly can also increase the disruption of human activities, through uncertainty, among other
causes.
Funding will be required to develop sound recovery plan guidance and the recovery plans
themselves. Unfortunately, recovery planning under the ESA has a history of large ideas and little
follow-through. Expenditures for recovery have increased in recent years but remain meager compared
with the billions of dollars likely to be needed to attain recovery goals for the bulk of listed species
(Department of Interior OIG, 1990; Jackson, 19921. The FWS appropriation to support recovery
programs was $10.6 million in FY 1990. For FY 1995, it was $39.7 million. More realistic budgets
are essential. Mechanisms should be considered to facilitate funding of complex plans, including
special funds for plan implementation and funding agreements with affected parties (e.g., private, state,
local, tribal, and other agencies).
We also suggest consideration of a new, comprehensive and continuing funding mechanism for
developing and implementing recovery programs for listed species. General wildlife and migratory
waterfowl programs at the federal and state level have been funded for decades through trusts based on
hunting and fishing licenses and the sales of arms and ammunition. Federal restoration programs for
hazardous waste sites, abandoned surface mines and the nation's coastal zone are similarly funded by
dedicated revenue sources. Some state acquisition and restoration programs are likewise based on user
fees and on real-estate transfers. These earmarked funding sources are widely accepted and successful
in providing stable revenue on which long-term planning decisions can be based. Planned programs to
recover listed species would benefit enormously from similar support.
The following description of the Natural Communities Conservation Program for the coastal
sage-scrub communities of southern California is an example of how many of the recommendations that
the committee has provided are being implemented in a program that could serve as a model for better
recovery planning and permitting under sections 7 and 10(a).
NATURAL COMMUNITY CONSERVATION PROGRAM AND
COASTAL SAGE SCRUB COMMUNITY OF SOUTHERN CALIFORNIA
Recent listings of the northern spotted owl, desert tortoise, fish species from the Sacramento-San
Joaquin delta estuary, and California gnatcatcher have affected economic activity in several regions of
California. Secretary of the Interior Bruce Babbitt has advocated new and innovative ways to avoid
these "economic train wrecks," favoring approaches that take a comprehensive view of endangered
species protection. His strategy for listing the California gnatcatcher by using a special rule under
Section 4(d) of the ESA in cooperation with California's Natural Community Conservation Plan
(NCCP) allows for moderate economic growth while conservation plans for the gnatcatcher are
developed that also consider other unlisted species in the coastal sage scrub.
The goal of NCCP is to conserve healthy functioning ecosystems and the species that are
supported by them. The pilot program for this process focused on the coastal sage scrub ecosystem in
southern California. Remnant, coastal sage scrub habitats support a diverse assemblage of native
animals and plants, including the imperiled California gnatcatcher, coastal cactus wren, more than 20
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The Role of Habitat Conservation ant! Recovery Planning
67
other vertebrate species that are candidates for federal protection, several invertebrate candidate
species, as well as nearly 100 plant species that are of special conservation concern.
The first NCCP was initiated with appointment of a scientific review pane! enjoined to outline a
conservation strategy for the coastal sage scrub ecosystem. While the scientific review pane! collected
extensive information on the coastal sage scrub community and its constituent plant and animal species,
it was not able to produce final scientifically defensible guidelines for long-range planning purposes
since the available database was limited. Instead, the scientific review pane! assisted in producing
interim planning rules that institutionalize several of the recommendations in this chapter, including the
interim protection of habitat crucial for survival until recovery planning is in place.
The scientific review pane! concluded that federal protection of the California gnatcatcher alone
would not be sufficient to confer protection to other species at risk in the coastal sage scrub
community. Indeed, it is highly likely that prohibition of take of the gnatcatcher under Section 9 of the
Endangered Species Act would not even serve to ensure the persistence of that species. Its highly
disjunct distribution demands conservation of ample amounts of coastal sage scrub habitat, including
habitat that is not currently occupied by the gnatcatcher, as well as conservation of other habitat types
to provide landscape corridors for dispersal by the species. In the absence of a regional,
community-level conservation plan, additional listings of coastal sage-scrub species would be inevitable
despite the listing of the California gnatcatcher.
Toward the development of a community-level conservation plan and focusing on three target
species of vertebrates (the California gnatcatcher, the coastal cactus wren, and the orange-throated
whiptai! lizard), the distributions of which embrace the majority of the planning area, the scientific
review pane! examined existing data and suggested additional information to be gathered that would
shed light on the coastal sage scrub community and the many species it supports. This multiple-species
planning effort attempted to use the best scientific methods available to:
1. Define the management planning region;
2. Identify subregional planning areas that consider landscape features, biological factors, and
political jurisdictions;
3. Describe an interim conservation planning framework for developing a viable system of
subregional reserves;
4. Recommend appropriate techniques for gathering baseline field data and their analysis;
5. Recommend research and monitoring activities to assist in subregional conservation planning
for individual areas; and
6. Recommend a selection process for a subcommittee of specialists to report on the best
available techniques for restoration and management.
Some data available in some portions of the planning area were of substantial immediate value to
subregional planning, but the amounts of information then available by and large were not adequate to
identify the physical characteristics of management areas necessary to protect ecosystem functioning
through time, to identify minimum viable population sizes for target species, or to describe effective
landscape corridors that would facilitate ecological interaction and gene flow among organisms that
occupy the coastal sage scrub community. The scientific review pane! therefore described a research
program focusing on six interactive research tasks.
1. Biogeography and inventory of coastal sage scrub. The basic extent ant! distribution of
coastal sage scrub vegetation and its constituent species are to be adequately mapped for the region and
for each subregion.
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Science and the Endangered Species Act
2. Trends in biodiversity. Monitoring of indicator taxa (such as coastal sage shrub dependent
birds, small mammals, and butterflies) will help to assess the ongoing success of coastal sage shrub
community conservation efforts. Relationships between species richness/composition and habitat patch
area, and the effects of isolation are to be investigated in sampling programs. These sampling
programs must include surveys for species richness and composition within a carefully selectee! series
of coastal sage shrub patches in each subregion.
3. Dispersal characteristics and landscape corridor use. Data from several locations within the
planning region are to be gathered cluring both breeding anti nonbreeding seasons on target species, top
predators, coyotes, and representative small mammals and invertebrates.
4. Demography and population viability analysis. Time-series data on the two target species of
birds are to be gathered in at least half the subregions and from representative physical circumstances
that span those found across the regional distributions of the species. Data must include territory size,
time budgets, reproductive success, survivorship, emigration anti immigration, with separate data
obtained both for males and females where possible. Population viability analyses are to be carried out
for sample populations and metapopulations, ant! should consider connectivity ant} environmental
effects.
5. Surveys and autecological studies of sensitive animals and plants. Basic information on the
location, abundance, distribution, and natural history of vertebrate ant! invertebrate candidate species
for federal protection and coastal sage shrub associated plant species of special concern are to be
gathered from select sites throughout the planning region.
6. Genetic studies. The maintenance of genetic variation is critical to the long-term viability of
species inhabiting coastal sage shrub an(l its assessment is an important aspect of population
monitoring.
The NCCP planning area is in lancts that have been greatly affecter! by human activities. Natural
and anthropogenic disturbances will continue; many of those disturbances will reduce the capacity of
coastal sage scrub habitats to support many species of concern. Areas designated as reserves thus are
unlikely to be self-sustaining (that is, provide for natural, dynamic ecosystem processes) or to be
capable of maintaining viable populations of target species without active management. The ability of
individual patches of coastal sage scrub habitat to be effectively managed over the long term will be a
critical factor in prioritizing of conservation efforts.
For these reasons and in recognition of the critical role of restoration activities in the Natural
Communities Conservation Planning Program, the scientific review pane} encouraged the immediate
creation of a committee to address central issues in management and restoration to focus on
I. Exotic species control, including animals and plants.
2. Recreational use of coastal sage scrub and other open space reserve areas, inclucling
identification of suitable tow impact recreational pursuits consistent with preservation goals.
3. The role of fire in natural ecosystem dynamics and processes, including the application of
managed burns and the control of ignitions of accidental and vandal origin.
4. Identification of restoration unit sizes, inclucting identification of maximum areas that are
restorable using current techniques. A focus on patch enlargement techniques is advised.
5. Identification of coastal sage scrub responses to soil conditions in restoration efforts, with
focus on soil structure, soil nutrient levels, organic matter content, water holding capacity, and soil
compaction.
6. Identification of appropriate seedling, outplanting, and irrigation techniques with focuses on
proper mixes of species, seeding techniques, and timing of applications of seed and irrigation.
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The Role of Habitat Conservation and Recovery Planning
7. Identification of techniques to encourage native herbaceous species and to discourage the
establishment of exotic species.
8. Establishment of realistic success criteria to evaluate management and restoration efforts
considering sage species diversity and cover, and use by target species.
During the interim period} while data are being gathered, land-use planning will continue. Draft
conservation planning guidelines therefore were published that describe short-term land use restrictions
for a limited period based on recommendations from the scientific review panel. Those
recommendations were meant to allow some development without foreclosing future conservation
options, and three key objectives are to be met during the interim data acquisition period.
First, development is to be limiter! to 5 % or less of the landscape that is occupied by coastal sage
scrub and its resident species. Development should also strive not to disproportionally affect any
"environmental subunit" (defined by vegetational subcommunity, elevation, slope, aspect, latitucle,
distance from coast, and substrate) within each subregional NCCP planning area.
Second, to the extent feasible, development is to avoid likely "hotshots" of biotic diversity (based
on habitat patch size and isolation).
Third, development is to not sever extant open space lanciscape linkages between biodiversity
hotspots.
Because threats to the persistence of species were viewed as so pressing, conservation planning
should result in no net loss of habitat value, defined as the ability of the coastal sage scrub habitat to
support target species in a subregion over the long term. Expected incremental losses of habitat
therefore must be mitigated with habitat restoration activities and effective management planning.
In acIdition, the scientific review pane! believed that long-term NCCP goals were to be best met
where six tenets of conservation biology are incorporates] at all spatial scales in regional and
subregional planning.
69
i. Species that are well distributed across their native ranges are less susceptible to extinction
than are species confiner} to small portions of their ranges.
2. Large blocks of habitat containing large populations of the target species are superior to small
blocks of habitat containing small populations.
3. Blocks of habitat that are close together are better than blocks far apart.
4. Habitat that occurs in blocks that are less fragmented internally is preferable to habitat that is
internally fragmented.
5. Interconnected blocks of habitat serve conservation purposes better than isolated blocks, ant!
habitat corridors or linkages function better when the habitat within them resembles habitat that is
preferred by target species.
6. Blocks of habitat that are roadiess or otherwise inaccessible to humans serve to better
conserve many target species than do roaded and accessible habitat blocks.
To differentiate between habitat areas that are likely to be more rather than less important to
long-term planning, a habitat-evaluation process was developed.
Habitats are to be differentiated into three categories. Those having higher potential
conservation value need to be i(lentifie(1 early in the planning process and protected frown habitat loss
and fragmentation while planning is under way. The methodology ciescribed in the guidelines places
50% of the coastal sage scrub in each planning subregion in the higher potential value category.
Habitats with intermediate potential value are those lands that probably cannot be managed as
independent reserves, but which by virtue of high quality or proximity or linkage to higher value
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Science and the Endangered Species Act
habitats should be treated as potentially significant for subregional conservation planning. Habitats of
lower potential value are those left after the higher ant! intermediate value areas have been identified
and include small, isolated patches, the loss of which would probably not affect the long-term viability
of the target species or other species of concern. Overall, an estimated 10%-25 % of the coastal sage
shrub in a subregion would fall into the lower potential value category. For the ranking approach to
interim habitat loss to function, it is important that a significant amount of land be classed as lower
value. The criteria for identifying higher and intermediate value land are to be adapted to local
conditions.
Each planning subregion needs to show interim protection for higher potential value lands on a
map, using a step-down process. Large, dense areas of coastal sage scrub are the higher potential
value lands. Natural lands that occur in linkages, that are close to possible higher value areas, or that
have high species richness are considered intermediate potential value lands. Remaining coastal sage
scrub is considered to have lower potential value. A guideline policy for local government treatment of
the higher, intermediate, and lower potential value lands during the interim period includes six
assessment criteria that address (in order) the presence of natural vegetation, the presence of coastal
sage scrub, the size of the scrub patch, its proximity to higher value lands, its role as a potential
landscape linkage or corridor, the densities of target species.
HABITAT-RELATED STANDARDS
Several habitat-related features of the ESA differ without basis in science. Prominent among
these are standards applicable to the protection of plants, and to the determination of jeopardy and
modification of critical habitat. As noted earlier, Section 9 fails to protect endangered plants from
habitat modification to the same degree that it protects animals. Plants, like animals, require places to
live and space for dispersal of their offspring. Plants include, for example, species isolated in unique
environments and others that disperse pollen, spores, and seeds over wide areas. The biological
differences between animals and plants underlying their taxonomic separation offer no scientific reason
for lesser protection of plants, nor do their importance to scientific and other research.
Under sections 7, 9, and 10, the FWS and NMFS are required to determine whether federal
actions or private actions that are federally permitted (Section 7) and nonfederal activities (sections 9
and 10) present an unacceptable threat to listed species and their habitats. Although the administrative
processes for making these determinations differ, these judgments are not distinguishable as matters of
biology and physics. Two scientific issues need very careful attention in the application of the
Endangered Species Act. The first concerns the differences and similarities between standards for
public and private lands and actions. The second concerns the relationship between survival and
recovery.
Public and Private Lands and Actions
Section 7 requires that federal and federally permitted actions do not jeopardize listed species;
Section 9 requires that private parties not take them. 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. The requirement of sockeye salmon for clean, cool water and of clapper
rails for safe nesting sites are not changed if they live on public or private land. A tidal marsh that
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The Role of Habitat Conservation and Recovery Planning
provides habitat for endangered species will be equally affected if it is filled by a public agency for a
public facility such as a sports complex or a marina, or by a private agency for a private facility such
as a shopping center or a hotel. Therefore, there is no biological reason to have different standards for
determination of "jeopardy," "survival," or "recovery" on public and on private lands.
This observation becomes particularly relevant to resolution of the controversy surrounding the
application of sections 9 and 10 to habitat modification on nonfederal lands. Whether or not Congress
intended sections 9 and 10 to regulate habitat modification on private lands is a legal question, but there
is no scientific question that a species may be as effectively jeopardized by habitat (levelopment as by
overharvest and that an endangered species program regulating habitat modification only on federal
lands will fail to protect many endangered species. The committee also recognizes that public agencies
and individual public servants on public lands behave differently from private landowners, both
corporate and individual, on private lands, because their rewards, incentives, and disincentives are
clifferent5. 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 for avoiding
endangerment and achieving recovery on public and private lands are probably needed.
71
,~
.
Survival and Recovery
The act and its regulations distinguish between species "survival" and "recovery" to determine
jeopardy to species and adverse modification of their critical habitat. Both determinations present
biologists with judgments that differ in degree, not in kind. Survival and recovery are points on a
continuum. Anything that jeopardizes species recovery makes survival less likely, although it might
still be likely over the short term; to make survival very likely, recovery must be ensured. Ensuring
survival for a short period is not equivalent to promoting recovery, especially for long-lived species
like razorback chub in Lake Mead, where populations can persist for many years without reproduction.
The difficulty arises when the concept of short-term survival is applied to determinations of jeopardy
and of effect on critical habitat with respect to federal actions, such as development of water resources,
which often have long-term, if not irreversible, effects. A decision, for example, to allow destruction
of one of three remaining habitats for a species predicated on the assumption that it will jeopardize
only recovery and not survival requires biologists to ignore threats to long-term survival by
irreversible actions. The impacts of activities with long-term or irreversible consequences should be
evaluated under a long-term standard. The relationship between survival and recovery should be kept
clearly in the minds of those who make and implement decisions. It is important to make estimates of
the probability of survival for given periods to help keep that relationship in mind.
CONCLUSIONS AND RECOMMENDATIONS
Habitat conservation and recovery planning are essential components of any program to protect
endangered species. To prevent delay and to allow immediate action to protect endangered species,
survival habitat should be designated for a period necessary to develop a recovery plan.
5For example, Mann and Plummer (1995) describe the destruction by private landowners of habitat on their
land that could support endangered species so that they can avoid the prohibitions of Section 9 or avoid the need
for a Section lO(a) permit for incidental take.
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Science and the Endangered Species Act
There is no biological or physical reason that standarcis relating to habitat protection, survival,
and recovery should differ for plants and animals and for public and private lands. The degree to
which public and private entities should bear the responsibilities of the Endangerecl Species Act is a
policy decision. But there is no escaping the scientific conclusions that all species have certain
biological and physical requirements no matter who owns the habitats, ant} that public ant! private
landowners do not always respond in the same way to laws, regulations, and other incentives and
disincentives.
Finally, survival and recovery are not equivalent standards, although they are related. 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. To permit a rational
evaluation of survival and recovery goals, it is important to provide estimates of probabilities of
achieving various goals over various periods, and the periods should be expressed both in years and in
generation times of the organism of concern6. It is also important that evaluation of long-term and
irreversible impacts be concluctec! in terms of long-term recovery of the species.
The committee recommends that the impacts of activities with long-term or irreversible
consequences be evaluated uncler a long-term standard.
The committee further recommencis that the relationship between survival and recovery be kept
clearly in the minds of those who make and implement regulations. To further that end, the committee
recommends that determination of survival and recovery contain good-faith estimates of the probability
of survival for given periods, perhaps 5, 10, ant! 100 years, as well as the probability of survival in
numbers of generations, perhaps 5, 10, an(l 100.
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, ant! it should also include advice on descriptions
of management options ant! application of risk analyses in consideration of alternatives.
REFERENCES
Andrewartha, H. G., anti L. C. Birch. 1954. The Distribution and Abundance of Animals. University
of Chicago Press, Chicago.
Beatley, T. 1994. Habitat Conservation Planning. University of Texas Press, Austin.
Clements, F. E., and V. E. Shelforcl. 1939. Bio-Ecology. Wiley, New York.
Elton, C. 1927. Animal ecology. Secigwickanci Jackson, London.
FWS (Fish and Wildlife Service). 1990. Interim National Conservation Planning Guidelines. U.S.
Department of the Interior, FWS, Washington, D.C.
FWS (Fish and Wildlife Service). 1992. Report to Congress: Endangered and Threatened Species
Recovery Program. U.S. Department of the Interior, FWS, Washington, D.C.
FWS (Fish and Wildlife Service). 1994. Preliminary Draft Handbook for Habitat Conservation
Planning and Incidental Take Permit Processing. U.S. Department of the Interior, FWS,
Washington, D.C.
Gilbert, L. E. 1980. Food web organization and the conservation of neotropical diversity. Pages 11
6Estimates of periods in years are important for planning of human activities and generation times are
important to provide biological realism to the estimates.
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The Role of Habitat Conservation ant! Recovery Planning
33 in M. E. Soule and B. A. Wilcox, eds. Conservation Biology: An Evolutionary-Ecological
Perspective. Sinauer Associates, SunderIand, Massachusetts.
Groombridge, B. (ed.) 1992. Global Biodiversity: Status of the Earth's Living Resources. Chapman
and Hall, New York.
Jackson, T. C. 1992. All creatures great and small. Legal Times December 7, 1992:20-23.
Jensen, D. B., M. S. Torn, and J. Harte. 1993. In Our Own Hands: A Strategy for Conserving
California's Biodiversity. University of California Press, Berkeley.
[ones, G. E. 1987. The Conservation of Ecosystems and Species. Croom Helm, New York.
Krebs, C. I. 1985. Ecology: Experimental Analysis of Distribution and Abundance. Third Edition.
Harper & Row, New York.
Mann, C. C., and M. L. Plummer. 1995. Noah's Choice: The Future of Endangered Species.
Alfred A. Knopf, New York.
McArthur, R. H., and E. O. Wilson. 1967. The Theory of Island Biogeography. Princeton
University Press, Princeton, New Jersey.
McNaughton, S. I. 1989. Ecosystems and conservation in the twenty-first century. Pages 109-120 in
D. Western and M. C. Pearl, editors. Conservation for the Twenty-First Century. Oxford
University Press, New York.
NRC (National Research Council). 1993. Setting Priorities for Land Conservation. National
Academy Press, Washington, D.C.
Pianka, E. 1978. Evolutionary Ecology (2nd ecl.~. Harper & Row, New York.
Tear, T. H., I.M Scott, P.H. Haywarcl, and B. Griffith. 1993. Status and prospects for success
of the Endangered Species Act: a look at recovery plans. Science 262:976-977.
Thornton, R. D. 1991. Searching for consensus end predictability: habitat conservation planning
under the Endangerec! Species Act of 1973. Environmental Law 21:605-656.
Van Home, B. 1983. Density as a misleacling indicator of habitat quality. I. WildI. Mgmt. 47:893-
901.
Whitford, P. B. 1949. Distribution of woociland plants in relation to succession and clonal growth.
Ecology 30: 199-208.
Wilson, E. O. 1992. The Diversity of Life. Harvard University Press, Cambridge, MA.
73
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Representative terms from entire chapter:
critical habitat
