United States
Environmental Protection
Agency
Policy, Planning,
And Evaluation
(PM-220)
20P-1001
"September f 99O
Threats to Biological Diversity
In The United Stati
Printed on Recycled] Paper
f f
*v*
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Threats to Biological Diversity in the United States
Based on a report by:
Elliott Norse, Ph.D.
Chief Scientist
Center for Marine Conservation
Prepared for:
Sally Valdes-Cogliano, Ph.D.
Science Policy Branch
Office of Policy, Planning and Evaluation
U.S. Environmental Protection Agency
Under EPA Contract #68-W8-0038
With Industrial Economics
Work Assignment #115
FINAL
September, 1990
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ACKNOWLEDGMENTS
Analyzing the threats to life on Earth is an ambitious task, one that no individual
should attempt without seeking the wisdom of others. This paper has benefited from the
critical insights and generous assistance of David Blockctein, Amie Brautigam, Marydele
Donnelly Michael Frankel, Kris Hansen, Roger McManns, Jennie Mbehlmann, Barbara
bhapiro, Geraldme-Tierney, Sally Valdes-Cogliano and five anonymous reviewers.
After leaving the author's hands, this paper was edited by Sally VahJes-Coeliano
of the Science Policy Branch of the U.S. EPA and Geraldine Tierney of the1 Bruce
, m£^y '«. A special focus on the threat of portion was added by Dexter Hinckley, also
of EPA's Science Policy Branch. * '
The cover artwork was submitted by Jon E. Miller, io the Office of Pesticide
Program's Endangered Species Design Contest.
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THREATS TO BIOtOGICAL DIVERSITY IN THE UNITED STATES
I. Summary. [[[ .. ......................... . ........... . ............. 3
II. Introduction [[[ . .......... . ............ ........7
A. Context.... [[[ .-, ______ . ________ . ................ 7
B. A public policy issue [[[ . ........................ .S]
C. Definition. .................................................. -. ..................... . ......................... 9
D. Patterns before human impact ............................ :. .............................. ;il
III. Threats ; ; 14
A. Responses to human impacts 14
B. • Determinants of vulnerability 17
C. Ultimate causes 24
D. Proximate causes 25
1. Direct population reduction
2. Physical alteration
3. Chemical pollution and solid wastes
4. Global atmospheric change
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I SUMMARY
tin, t^5 w°rld™de treats to. biodiversity increase and extinction rates rise to 1000
times the natural background extinction rate, the conservation of biological diversity is
emerging as a major public policy issue. The ever-expanding human population, the
nSfrS6i caPf\c°™umPtion of g°°ds, and the greater impacts of pollution on
™ V! f ' ^ #?ba] ***** *** mcreasingly stressed the living .systems which
provide humans with food, raw materials, medicines, breathable air, drinkable water
current climatic patterns and aesthetic pleasure. ' .- i "cw<«er,
Building on realizations over the last two-decades that technological
advancements are degrading a potentially fragile natural world and that whole
ecosystems are endangered, the biodiversity movement surfaced in 1979-80 with the
publication of several landmark documents, including The_Snldng.^rk by Norman
Myers, Thomas Lovejpy's extinction section of TheGlobal 2000 Report tn tn»
and Conservation Bioloev^m F.vnlntinnarv-Emlnpiral P.rc^,,, c^!r °
Biological diversity refers to the variety of life on all levels of organization
represented by the number and relative frequencies of items (genes, organisms and
ecosystems) Perhaps the most useful definition involves these three levels- 1} genetic
fnd6?)1^T^temPdiverl? SPedeS -diversity' °r th^ Pumbers and frequencies of species;
settings. Unlike wildlife management or endangered species protettion, practices which
strive to protect only certain favored species, conservation of biologicaJI diversify
recognizes species, genotypes and functioning ecosystems as valuable resources and
recognizes communities of organisms as interactive complexes to be preserved.
In a policy sense, the concept of biological diversity represents a potential
measuring tool for the preservation of biological integrity. Measurement of biological
S^nS? Provide an effective and economical indicator of overall ecological health
and help ensure that adequate protection of ecosystems is achieved
how Penn^6 ^^^ anthropogenic threats to biodiversity, it is useful first to examine
how genotypes, species and ecosystems respond to anthropogenic stress in general and
to examine what factors determine vulnerability to anthropogenic stress. Hurntn
activities reduce genetic diversity by eliminating whole populations of organisms, by
reducing populations to the point where genetic drift overtakes natural selection as a
dominan evolutionary force, and by creating new selection pressures. Species exposed
to irresistible anthropogenic stress may become increasingly rare, locally extinct, and
eventually extinct throughout their range. Ecosystems tend to employ selfSaSng
mechanisms that enable them to withstand some natural stresses with little ofno effect,
ec
stresear T T* ^^ StTQSS&S which d° have an effect' but anthropogenic
stresses are often drastic and quick enough to overwhelm this self-regulation.
Many factors determine vulnerability of species. Some are iiiher'ent properties of
the organism or species and impart vulnerability whether the stressor be naturTor
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anthropogenic; others result largely from the nature of anthropogenic" stressors. Many of
these factors are correlated, but can exist independently (e.g. many species of large
organisms have small populations, but both factors, large organism size and small
population size, can independently cause vulnerability).
Species with small effective population size (referring to the number of breeding
males and females) are vulnerable for demographic (e.g. unbalanced sex ratios) and
genetic reasons (e.g. limited gene pool, subject to genetic drift). This may be the
primary risk factor, especially hi recently reduced populations. Species with a narrow
geographic distribution, those with large area requirements, and those "amphibious"
species requiring more than one type of habitat are at increased risk that sdjrrie stressor
will infringe on at least one of their habitats.
Specialists, requiring a particular type of habitat or food, and species intolerant ol
disturbance are at greater risk due to their inflexibility. Species of large organism size
are vulnerable despite the advantages of large size because many natural and
anthropogenic stressors (e.g. hunting) select against large organisms. Organisms with
slow reproductive rates are more vulnerable to increases in mortality. Evolutionarily
naive organisms that have evolved in the absence of competitors, predators and diseases
are more vulnerable to the accidental or intentional introduction of such organisms.
While factors imparting vulnerability to species are the most well-known, factors "
increasing vulnerability to sub-specific populations and genotypes., and to ecosystems,
must also be addressed. Each factor listed above may also affect sub-specific
populations. Broad principles concerning genetic determinants of vulnerability are not
well defined, but genes conferring the ability to reproduce early would increase fitness in
populations heavily exploited by humans.
Six factors are primarily involved in imparting vulnerability among ecosystems.
Impermanent ecosystems, particularly those that are actually successional stages, are
vulnerable to human activities which intentionally or unintentionally prevent natural
disturbance or succession (e.g. fire suppression). Oligotrophic ecosystems (those in
which nutrient elements are scarce and limiting to many organisms) are vulnerable to
changes in nutrient availability (e.g. increases from fertilizer use, sewage discharge).
Undersaturated ecosystems, exhibiting fewer species than might be expected due to
current 'isolation or historical reasons, may contain vacant niches and naive biota which
are vulnerable to invasion. Isolated ecosystems, such as islands, are vulnerable because
extinction is not fully offset by outside colonization. Ecosystems of small size sustain
fewer species than a region of similar size within a larger ecosystem due to penetration
of external influences. The most important risk factor is probably proximity to human
populations. Ecosystems suffer as human populations appropriate land and resources
and produce harmful wastes.
Most current and pressing environmental problems, including the biodiversity
crisis, primarily result from two trends: the exponentially increasing human population
and the increasing per capita consumption of the Earth's resources to provide for human
needs. These ultimate causes are manifested in six proximate causes representing the
major anthropogenic stressors to biological diversity.
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*"*
- nng,
orgamsms during hunting, traroi™ e c ) X in^? (<5W™1« « ™ng of non-taVget
reducnon in some manner to prevent oveMmS^f6'1 nations now Umi« «««
exploitation remains a major stressor to fJ™? 1 End have heen ^icated in
and turtles. Organisms feeding at o?near tHe ton nf't^T ? ?arine manunals' birds
"s^°/fc substances which bioLc^muTate(e7 f9°dt<*ain are particularly at
Wildlife Refuges are safe from thes™a s StJ£ }H uOt 6Ven the National
contamination in these reserves followir « S ? evidenced by a ^cemt survey of
Kesterson Refuge. °I1OWing the dlscoveiy of chemical contamination in the
globa, amsrr^^^ de- Bating threat to biodiversity is
radiation. Predictions of waring a^Trefate^ TcH^t^ ^ 6nhanced ultraviolet-B
uncertain, but it is probable that Sm^ e^l ?StlC Change
Addmona,,,, higher a^ospheric
DNA and immune 111''65'
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fc™.c 2? mtr°duction of an alien species can upset ecosystem functioning due to new
^c^iP?tran' Predatl°n and- diSeaSe °r due to more indirect facto«- While alien
species usually do not survive upon introduction into a new habitat, those that do surrive
^I^l^^1^ '? ?ounsh.in a new haWtat devoid of their natural enemies. ^Ten
species have been most destructive to naive and undersaturated biota, such as in HawaH
In general, terrestrial and freshwater organisms are more likely to be affected than
marine species, as their populations are more localized.
tWat ^ ?e maSnitude ^d SCJPe of these threats continue to increase, and as new
teats continually^ppear, interactions between stressors will become more ii^ortL.
y n°HWeU StUdl,eil.0r ^derstood, interactions between two or! more
?£ ?FOd1!1.Ce. cumulatlve effects wl"'ch are far more destructive than the
threats; this interaction must be considered to ensure adequate protection.
An overview of the effects of 13 stressors on 59 categories of organisms in the
contiguous 48 states appears in Table 2. The effect of eaclfstressor on ^Ltegory of
organisms is rated as negligible/minor, substantial meriting study, or very serious
^"JZES? T11^11- Tabl! 2 rePreSentS the ^st estimate of the author, Elliott
SKo inT d ^l1^11 10 the Opinion of avian ecol°gist David Blockstein:
1 able 2 could be unproved at some future time by accounting for geographic differences
showing change in stressors over time, incorporating effects of interactive stressors
£?l±f
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II INTRODUCTION
A CONTEXT
Roughly 3.5 billion years of evolution 'have left the earth host to perhaps 5 to 30
million extast species (Wilson, 1986). In many ways, these organisms and their forebears
have shaped the.world.of today. Inheriting an atmosphere laden .with carbon monoxide,
carbon dioxide, methane, ammonia and cyanide, living organisms converted it to one of
nitrogen and oxygen.. Some of this oxygen reacted to form an atmospheric layer of
ozone, which screened out ultraviolet radiation that had scourged the planetary surface.
j
Living things decomposed ro ;ks into fine particles and added organic material,
creating the world's soils. Vast amounts of atmospheric carbon dioxide were sequestered
in oil, coal aad limestone, thereby turning down the temperature of the global
greenhouse. Much of the planetary surface was covered with trees, creating moderate
microclimates and a diversity of spaces in which living organisms could hide from harsh
conditions and one another. By creating breathable air, productive soils, a suitable
climate and useful substances such as foods, fuels, raw materials and medicines, the
Earth's plants, animals and microorganisms fashioned an environment in which Homo
sapiens could originate and prosper.
Likewise, Homo sapiens has further transformed the earth; being uniquely adept
at changing the world to suit its own needs. For most of human Mstory, humans have
been essentially powerless against predators, storms, droughts, famines and diseases.
Currently, modem technology has provided many with relief from these stressors, as
witnessed by the exponentially increasing human population, but recognition is rapidly
increasing that modern lifestyles have great environmental costs, j
The ever-expanding human population, the increasing per capita consumption of
goods, and the greater impacts of pollution on local, regional and global scales have
increasingly stressed living systems, eliminating many species and entire ecosystems. The
human population is currently doubling every 40 years, forcing continued expansion onto
more marginal lands and displacement of the natural inhabitants and perhaps causing a
mass extinction of life like none that has happened on Earth in at least 65 million years.
The average background rate of extinction before human intervention was
approximately 1 species per year; this figure was below the average rate of new
speciation, resulting in a net increase in species throughout most of history. The current
rate of extinction may be one thousand or several thousand species per year; this figure
is significantly higher than the rate of new speciation, thus resulting in species depletion.
Indeed, in the past the loss of a species has generally allowed for the emergence of one
or more new species, resulting in a net increase. This is no longer true, as species which
took tens of thousands of years to emerge are being extinguished and replaced by the
proliferation of a single species (Myers, 1989). .
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the *veDrs^^ —in reliant on
current climatic patterns, and awSSSsSS?^??' f We **' drinkable water'
Deration, pollution and other mS of dTsh^n?^ ^^'^^ation, physical
*>e earth, Homa^iens is eMnSng tihfSSrf ta ±Sff / **"**** °n
its own long-term survival and wen-being! may be threatening
biology lacks accurate and
threats, the effects^ ^SsS^^S^^^8 ecosystems, the severity of
and economic costs of mffit " &ms' ** the social
an economic costs of mtt " ^^&ms' ** the social
generations. 5 y s llKev lo be of great value to this and future
^
B A PUBLIC POLICY ISSUE
,
emphis on conserving biologl d UkeTS,™? " Sma" but «""*«
epudh °f «°
centmy the Umted States be^n SectiS : ^ IStS™"^, ^^"S in the last
national park system. Together the eS % ^ speclal scenic ^'"es in a
and tods of gXa, ^
two deos °be8an ""« hoM -»«
tha, gave rise
Carson p-"^
8
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The third realization dawned suddenly when U.S. Apollo sistronauts sent back the
first pictures of the small, seemingly fragile Earth within the vastness of space. Many
people remarked that these pictures changed their consciousness about the fmiteness and
vulnerability of the world in which we live. The fourth realization, held largely within
the scientific and government communities, was that whole ecosystems were rapidly
being destroyed, including the supremely diverse tropical forests:
The ensuing biological diversity movement seems to have had five rather
independent but almost simultaneous origins. In 1979, Norman Myers published The
ginking Ark, which examined the worldwide extinction of species of all tax& not just the
extinction of mammals and birds which had concerned previous writers. Included were
the first estimates of global extinction rates. In .980, the Council on Environmental
Quality and the State Department collaborated on The Global 2000 Report to the
President, which contained a groundbreaking section by Thomas Lovejoy on global
species extinctions as a consequence of tropical deforestation.
That same year, the Council on Environmental Quality's Eleventh Annual Report
contained a section entitled "Ecology and Living Resources-Biological Diversity" by
Elliott Norse and Roger McManus (also published separately as Biological Diversity^. In
1981, Paul and Anne Ehrlich published Extinction-the Causes and Consequences of the
Disappearance of Species, a clarion call for conservation that reached a wider general
audience. At the same time these assessments were being presented to the general
public and government decision-makers, Michael Soule and Bruce Wilcox (1980) were
editing and publishing a landmark volume, Conservation Biologv-An Evolutionary-
Ecological Perspective, a volume of scientific studies directly relevant to the extinction
crisis, which gave the name to the newly coalesced science of conserving biological
diversity.
i
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agriculture), while degradation is reserved for the reduction in quality or productivity.
While this is a valid distinction, it must be recognized that degradation is often a
component of conversion; the removal of natural vegetation during conversion degrades
the ability of the ecosystem to provide ecosystem services which can be vital to the
maintenance of any life.
Furthermore, the replacement of climax or specialist species by lower successional
or opportunist species should not be misconstrued .(as it .sometimes has) as an increase in
biodiversity. As David Wilcove (1989) notes, while disturbance of ancient Pacific
Northwest forest might attract enough lower successional and opportunistic species to
increase species richness on a particular tract, this is not an increase in biodiversity. The
amount of logging in this area ias left no shortage of habitat for open-country species
such as dark-eyed juncos and brown-headed cowbirds, whereas the species associated
with old-growth coniferous forests are diminishing.
Clearly, biological diversity is not just a numbers game, and there is more .to
preserving biological diversity than conserving only the areas richest in species. Rather,
maintaining biological diversity means maintaining the integrity of the genetic structure
within populations, the richness of species within ecosystems and the mix of ecosystems
that prevailed before human impact in all regions of the Earth's surface. This goal is
implicit in any sound definition of biological diversity.
In a policy sense, the concept of biological diversity represents a potential
measuring tool for the preservation of biological integrity. Ecologists commonly assess
the severity of pollution stress on community structure by measuring either reductions in
overall species diversity (species-level biodiversity) or changes in the abundance of
indicator species. Indicator species fall into two categories: "decreasers" (those sensitive
to the pollution stress) and "increasers" (those tolerant of the stressful conditions which
expand into niches vacated by decreasers).
i
D PATTERNS BEFORE HUMAN IMPACT
Since very few of the world's ecosystems were studied before they underwent
substantial alteration by humans, the assembling of a global picture of the pre-impact
world's biota is largely an exercise in combining information from paleoecology and early
written accounts with inferences based on what is currently known,. For example,
historical records and current knowledge of community ecology and biogeography lead to
the conclusion that the cool temperate, moist, well-drained Central European lowlands
that now support farms and villages were dense, continuous deciduous forest at the time
of the Roman Empire.
Such an exercise requires considerable conjecture. For one; thing, there are major
disagreements about what kinds of ecosystems were located in which regions before
human impact. Were the tallgrass prairies once extending from the Gulf Coast to the
prairie provinces of Canada the natural ecosystem in that zone (a result of lightning-
caused fires and grazing by bison) or were they created by Native Americans who burned
11 I
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the vegetation (and eliminated trees) to improve forage for game animals? Much the
same question could be asked about lands that are now tropical savannas in northern
Australia.
Likewise, while humans were spreading from Africa to other parts of the world,
contemporaneous climatic changes were occurring which could also have caused biotic
changes. While the importance of climate change in determining ecological patterns
must be recognized, coincidence between North American large mammal disappearance
and the rapid advance of humans possessing potent new hunting tooL suggests
anthropogenic factors played some part. There is evidence that similar mass extinctions
of mammals and birds occurred at quite different times shortly after humans colonized
South America, Australia, Madagascar, New Zealand and Polynesia.
Megafuana extinctions of this magnitude did not occur in Africa and Asia, where
early humans resided long before they invaded the lands listed above. Roughly 19% of
the large mammalian genera in Africa were extinguished compared with 74-86% in
North America, South America and Australia (Martin, 1986). Presumably, human
capabilities evolved slowly enough during the early Pleistocene to allow most of the giant
animals of-Africa and Asia to persist. By the time Homo sapiens arrived in the
Americas, Australia and various islands, they were far more effective at hunting large
prey. This would explain why some African and Asian elephants remain, but no North
American mammoths or mastodons.
Except for changes wrought by man-made fires, the major impact of pre-
agricultural people was probably on the species they hunted for food and those species
that competed with humans for prey. Most other major ecological changes between the
evolution of the genus Homo and the first agriculture probably resulted from changing
climate.
What did the world's biota look like before human impact? Not surprisingly, it
was a lot richer. North America, for example, hosted glyptodonts (an ox-sized armadillo-
like mammal), giant ground sloths, several kinds of proboscideans (elephant-like
mammals), a giant deer (Cervalces sp.), large camels, large musk-oxen, horses, a lion
(Panthera leo atrox\ a sabre-tooth tiger (Smilodon fatalis). a powerful, short-legged wolf
(Canus.dirusX a gigantic short-faced bear (Arctodus simus)r and a bear-sized beaver
(Castoroides sp.) (Kurten, 1988). Steller's sea cow grazed subtidal algal pastures from
California all the way to the Aleutians and across to coastal Siberia. In the first
centuries after humans arrived from Asia via unglaciated areas in Alaska, these
megamammals were swept away with lightning speed. By 10,000 years ago, all these
animals were extinct (Martin, 1986) except the sea cow, which held on in its last remote
island redoubt in the Bering Sea until 1768.
Until the coming of the Europeans, highly diverse eastern deciduous forests of
very large oak, chestnut, beech and maple reached from the Atlantic to beyond the
Mississippi, and were home to billions of passenger pigeons, along with-wolves, mountain
lions, elk, moose, a few bison and, in the South, ivory-billed woodpeckers and Carolina
parakeets. Eastern rivers ran thick with Atlantic salmon. The vast tract between the
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now sagebrush or mesquite-covered deJn
throughout most of these we*ern ^s tods
m Averse coniferous forest whose
dtameter; California condors
prairie;
western areas that are
grizzly ^ »*««>
was solidly do^
"" ""l 2° te in
eweou ? mperate ^ and ustr^ were
^ from fte Nonh
Much
Sn Lanka,
southern Asia to
AustraUa were Seriously
savanna and hosted a remarkable
flightless elephant bird T^
on Earth and laid eggs holding^norTZ
1981). Densely foref It I NewSnd
- -.-. ,,.?t and tree
lemurs and the 1100 pound
largest bird that has ever lived
., survived until about 1700 (Day
an extraordinarily rich endemic avifauna
moas). the IarP«t «* which reached 13
the most endemic
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Ill THREATS
A RESPONSES TO HUMAN IMPACTS
Human actions threaten all levels of biological diversity. The most visible level
should be ecosystem diversity, but limitations on human spatial and temporal horizons
make it difficult to. comprehend changes occurring on this level. The magnitude ot
ecosystem destruction is made more visible by technological innovations such as satellite
imagery; the remarkable Landsat photographs-between 1973 and 1988, for example, show
rampant deforestation in Brazil's state of Rondonia (see National Geographic, 1988).
Less visible but better appreciated is destruction of species; it seems images of vanishing
con-lors and elephants elicit more human response. Least visible and least understood is
the loss of genetic diversity.
s .
Human activities reduce genetic diversity in at least three ways. Anthropogenic
disturbances can 1) eliminate whole populations of organisms and their entire genetic
complement; 2) reduce population sizes to the point where genetic drift overtakes
natural selection as the dominant evolutionary force; and 3) create new selection
pressures.
Each species is comprised of one or more relatively distinct populations of
interbreeding individuals. Genetic distinctions may arise between populations because
some kind of barrier diminishes or prevents genetic exchange between organisms of the
same species. As a result, individuals within one population may possess versions ot
genes (alleles) that are absent in another population, or they may possess the same
alleles in different frequencies. The different alleles that code for varied expressions of
a particular trait provide the raw material for evolution. Some combinations of alleles,
called co-adapted gene complexes, are particularly important because, as a group, they
confer adaptation to local conditions.
Many people do not understand the importance of preserving populations. If
marbled murrelets (a species of small seabirds) still abound in Alaska, they wonder, why
should we worry about their elimination in California? They fail to recognize the genetic
diversity at stake. As Paul Ehrlich (personal communication) and others have pointed
out, humans are causing the extinction of populations at a rate far greater than the
extinction rate for whole species. As populations disappear, their distinctive alleles and
co-adapted gene complexes are lost, as are the products and ecological services that
populations provide. The Endangered Species Act of 1973 appropriately recognized that
populations merit conservation even if they are not morphologically distinct enough to be
called subspecies.
Populations which are not driven entirely to extinction, but which are stressed
enough to dramatically reduce population size, may be further affected by genetic drift.
Genetic drift is the change in the frequency of various alleles caused by-random chance
rather than by selection pressure. In small populations, genetic drift can become more
important relative to the natural selection that tends to maximize the fitness of
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individuals, because certain individuals contribute disproportionately "ti> the gcac pool of
succeeding generations by pure chance. This can result in the loss of beneficial (or
detrimental or neutral) alleles, and in the fixation of detrimental (or beneficial or
neutral) alleles. Thus, this non-Darwinian form of evolution can reduce genetic fitness
and diminish the potential ability of an organism to withstand chainge.
Additionally, human activities can reduce genetic diversity by altering-setection
pressures. .Living things evolve (i.e. their gene frequencies change) in response to
selective pressures and opportunities in then- environments. Anthropogenic influences
have created new selection pressures.
Examples are abundant. Before the industrial revolution, virtually all peppered
moths (Bi$ton betularia) in Europe were light ashy gray matching the lichens and tref
trunks on which they rested. As Europe industrialized, sulfur oxides emissions from coal
killed off lichens, and the tree trunks turned black with soot. The peppered moths that
survived in heavily polluted areas were also sooty black. Light-colored individuals made
easy prey for birds, and were selected against. \
The aurochs, the ancestor of domestic cattle, was a large, powerful, fierce creature
capable of living through the rigorous European winters. Domestication by humans
selected against many behaviors, and many strains of domestic cattle have lost their
ancestors' abilities to find food covered with snow and to eat snovy to obtain water. The
aurochs and the genes that produce such adaptive behaviors are now extinct.
When first introduced in the 1940s, the pesticide DDT was hailed as the savior of
the many millions of people who would otherwise die each year of insect-borne diseases
such as malaria. DDT, however, selected out the most susceptible individuals, leaving
less susceptible ones to pass on their genes. iNow the mosquito vectors of malaria are
resistant to DDT and many other pesticides, and malaria affects hundreds of millions of
people worldwide.
The ancestors of modern-day corn were Middle-American perennial grasses which
scattered their small production of seed each year. Today's highly selected annual corn
produces huge crops of seed and then dies each year, but is unable to reproduce without
human.help. The seeds stay attached to the corncob, so any cobs that escape harvest
produce densely crowded seedlings that cannot avoid severe competition. This would
quickly lead to extinction if humans did not remove and disperse them. The ancestors of
corn were long thought to be extinct until a handful were discovered in the late 1970s.
Human contact has intentionally or unintentionally altered gene frequencies in all
these organisms, increasing some genes at the expense of others. Some organisms have
prospered; corn plants and cattle are undoubtedly more abundant than their ancestors
were. Many species, including some that we consider "wild" such as house sparrows,
head lice, dandelions or coconuts, undoubtedly would be much rarer if humans
disappeared. Far more have not prospered from the advance of humans, and very large
numbers of genetically distinct populations and their genes have disappeared entirely.
i
15
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numerous SgC *Z^& £$£**« of their 'range, become less
^
speoes because the definition -'t':^- °f *"" °r
each of which ca£ be further (^^^5ffiy5teailf ***?* Md Australasian),
forests extending, west of the AndeTare fairlv dhtiJS £n T'05' *? Central American
or of southeastern Brazil. Within the CeS 5S2^55 ^ °f the ^^^ Basin
forests can further be divided into evewttn^^^ff^ C°ast forest **&*•
dn ^ f St Iowland forests' (and **>
-r ^OreStS' seasona% dry deciduous
11 *
e nto eve
mangroves, seasonally flooded montan
forest, and usually dry thorn
and all of these a^e SS
between them to facilitate the
Th*"" within *hese Agones,
mild stresses and to recover
beyond a certain point. In the
northwest California, a -SS
thousands of years, traditional, natural
individual trees and other organisms but
forest create a moderate mi
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B DETERMINANTS OF VULNERABILITY j
The eastern elk that once roamed the land east of the Mississippi are now extinct
(Thomas and Bryant, 1987), but white-tailed deer are more abundant than ever. Only a
few thousand spotted owls survive in the Pacific Northwest, but barred owls have invaded
and are spreading throughout their range (Norse, 1990). Amazonian upland terra firme
forests are disappearing even faster than nearby floodplain-varzea forests (Low, 1984).
Although fewer than 20% of the world's .birds occur on. islands, more than 90% that have
become extinct in historic times are island species (Low, 1984). These situations raise
the question: What determines the vulnerability of particular genotypes, species and
ecosystems? . y'
There has been remarkably little research into most aspects of vulnerability. As is
typical in discussions concerning biological diversity, most attention has been directed
towards losses at the middle level (species extinction), but differences in vulnerability
among genotypes within species and among ecosystems must also be considered.
Some differences in vulnerability are inherent; the organisms or ecosystems would
be more vulnerable whether their stressors were natural or anthropogenic. Others result
largely from the nature of anthropogenic influence.
Most important insights concerning vulnerability have been, drawn from studies of
island species, from both oceanic islands (those always isolated from land) and from land
bridge islands (those cut off from mainlands, often as a result of post-glacial sea-level
rise or creation of reservoirs). Some factors that determine vulnerability in species are
correlated. For example, many species of large organisms have small populations, but
small population size is a major determinant of vulnerability regardless of organism size;
conversely, large size can make a species vulnerable independent of its initial rarity.
1. Determinants of vulnerability among species |
a) Small effective population size. All else held equal, small populations are more
vulnerable than large ones for a variety of reasons (Frankel and Soule, 1981). Some are
demographic (e.g. unbalanced sex ratios) which are more likely in smaller populations;
short of resorting to hybridization, there was no hope of perpetuating the dusky seaside
sparrow when the population fell to five individuals, all of which happened to be male
(Cade, 1983).
i
Demographic vulnerability is not merely a question of the sex ratio, but of the
number of breeding males and females (connoted by "effective" population size). Grizzly
bears in the greater Yellowstone ecosystem number perhaps in the 200s, but-many are
too young or too old to reproduce. The effective population size iis much lower because
only 30 or so are reproductive females. Thus, age structure is a second key demographic
variable that can render small populations vulnerable.
-Furthermore, populations fluctuate in response to environmental variables that
might or might not be obvious. A large population can lose 90% of its individuals and
17 i
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still have a good chance of recovery if its habitat remains intact. Conversely, normal
fluctuations in a small population can lead to demographic imbalance and extinction.
Some groups, such as butterflies (Ehrlich, 1983) might be particularly vulnerable to
demographic fluctuations leading to extinction.
^riHin^SfS18^; ^iSS goneti^ reasons why sma11 Populations are vulnerable
(Schonewald-Cox et al., 1983). Smaller populations are less likely to possess rare genes
As conditions change, rare genes may confer improved fitness (the improved ability to '
reproduce successfully). The presence of rare genes can be a vital fork of evolutionary
insurance, thus their absence makes a species more vulnerable. Additionally, small
populations are subject to genetic drift, as previously discussed. Genetic drift can
dimmish fitness (Franklin, 1980).
Rarity exists for many reasons, including some which are simple consequences of
high species diversity (Cody, 1986); thus rarity per se is not always harmful for a species
Some naturally rare species have special mechanisms allowing persistence at low
densities (Rabinowitz et al 1984). However, formerly common species which have been
artificially reduced are much less likely to possess mechanisms such as these.
Small population size, especially in a population whose numbers have been
recently reduced, is probably the most important risk factor for extinction (Terborgh and
Winter, 1980). Countless species have had their populations reduced by human
activities.
b) Narrow geographic distributions. Abundance is determined by a combination of
three factors: 1) size of geographic range, 2) number of utilized habitats; and 3)
individual population size (Rabinowitz et al., 1986). A species can be termed rare by
£lC1Sn ** T?6?? fa.lt0r?' Spedes such M western red cedars and mountain lions
have broad geographic distributions and occur in many kinds of habitats but typicallv
have low densities. Others, such as red mangroves and canyon wrens have broad
geographic ranges but occur only in rare, localized habitats. Still others, such as
Haleakala silyerswords and Devil's Hole pupfish are classic endemics (species found only
in a restricted area). J
M, ru ^ °i_ther factors beinS e(lual> a narrower geographic range increases the
likelihood that some natural or anthropogenic stressor may cause extinction. Human
proliferation has significantly reduced the geographic range of a great number of species.
c) Large area requirements. Species of large organisms need more resources than small
ones and tend to range widely to find them; other species depend on resources that are
widely scattered over a large area. Species such as these are vulnerable to any stressor
that decreases the size of their habitats. Grizzly bears, spotted owls, and Florida
panthers are currently endangered because ranching, logging, and housing development
have eliminated most of their habitat and isolated them in small, island-like refuges.
d) Specialization. -Specialists requiring a particular -type of habitat, or food are especially
vulnerable. One famous example is the Everglade snail kite (Rostrhamus snrfahiifc), a
18
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species endangered due to its dependence on a single prey, the apple snail (Pomacea
paludosa) (Takekawa and Beissinger, 1989). As the hydrology of the Everglades has
been altered for agriculture and housing development, apple snail habitat has
disappeared and the monophagous raptor has diminished. Many specialists have
decreased as a result of human activities.
e) Intolerance of disturbance.. Both the frequency and type of disturbance occurring in
natural ecosystems exert enormous influence on plants, fungi and animals. In general
disturbances increase populations of species that are able to tolerate disturbance or take
advantage of the newly available resources in recently disturbed areas. Many of the
these are opportunistic, "weedy" species, such as dandelions and the red imported fire
ant, which devote a relatively large percentage of their biomass to reproduction and
produce many young (r-selected species). In a climax community, these are often kept in
check by competition with species which devote more energy to the growth and
maintenance of the adult (K-selected). Disturbance shifts the scales, and "weedy"
opportunists flourish while climax species 'such as the western red cedar, myotis bat and
the northern spotted owl, disappear. i
f) Large size. Species of large organisms often have small populations and large area
requirements, but they can be vulnerable for other reasons as well. This might seem
counterintuitive, as large size can confer resistance to forces that harm smaller
individuals. For example, giant sequoias have very thick bark thai: makes them virtually
immune to the frequent fires that kill many thinner-barked trees.
However, many forces select against large species, (e.g. wind which selects against
the tallest trees, and predators, which often take the largest prey they can readily
handle); (see Council, 1975). Humans, too, tend to hunt large prey (such as deer) and
log tall, large-diameter trees (such as sugar pines); humans are especially likely to
discriminate against large species because modern technology can diminish any natural
advantages conferred by large size, while our economics demand that we maximize
return for unit effort by taking the largest individuals possible. That is why blue whales
were pushed towards extinction before the smaller fin whales, which were depleted
before the still smaller sei whales, which were hunted to low levels; before killing
commenced on the smallest baleen whales, the minkes (Ehrlich et al., 1977).
g) Slow reproductive rate. There is enormous variability in rates of reproduction. Two
species can have equal abundance if one reproduces faster but the other has lower
mortality. If conditions change so that their mortality rates become similar, the faster
reproducer will be better able to recover from disturbance. Faced with increased
mortality from off-road vehicles, desert tortoises are hindered by their inability to
reproduce until they reach 12-20 years old (Campbell, 1988). A look at the Endangered
Species List will show many species with unusually low reproductive rates.
h) Evolutionary naivete. Organisms which evolved in isolation from competitors
predators, or diseases are more vulnerable. This is most obvious with island species such
as plants lacking physical or chemical defenses against grazers, or defenseless birds such
as the kakapo (Strigops habroptihis). a very large, flightless, ground-dwelling and
critically endangered parrot from New Zealand.
19
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Similarly, anthropogenic stresses can render even mainland species "naive".
Striped skunks and adult eastern box turtles have evolved natural defenses to protect
themselves from foxes, cougars, black bears and many other natural predators, but not
from speeding cars. Many species are defenseless against man-made chemicals in their
environments. Industrial wastes, insecticides and herbicides can jeopardize many species-
-perhaps most except herbivorous insects-that are not adept at breaking down novel
substances into non-toxic ones.
i) "Amphibious" habits. "Amphibious" organisms, whose life cycle or habits require more
than one type of habitat, run greater risk of losing one of these habitats to natural or
anthropogenic disturbance. The vertebrate class Amphibia is hardly alone ui this; "living
double (or multiple) lives" is very widespread. Nevertheless, this is one of the less-
discussed determinants of vulnerability among species. Reed Noss (1987) notes:
Field naturalists recognize that many animal species require distinctly
different habitats for different activities or separate stages of their life
cycles. Some organisms, such as holometabolous insects [those which
undergo complete metamorphosis] and many amphibians, undergo
• • —-ontogenetic niche shifts [shifts related to development] that place them in
drastically different habitats after metamorphosis.... Other organisms...
commute between different patches or community-types to meet life history
needs.
In the class Amphibia, the most familiar life history is exhibited by spotted
salamanders; adults live in moist places on land but lay eggs and undergo larval
development in water. This species is vulnerable to either elimination of the large fallen
logs under which they hide—which happens in intensively managed forests—or from
pollution of then- breeding ponds from acid rain.
Migratory species are also amphibious, whether they move seasonally between
uplands and lowlands, as do mountain goats and some elk populations, or migrate long
distances, as dp hundreds of bird species that breed in north temperate zones but winter
in tropical regions. Many populations of migratory songbirds seem to be decreasing, but
whether this decrease is due to loss of their tropical forest wintering grounds, to pesticide
poisoning in their North American summer grounds, or to some other factor or
combination of factors, remains to be determined.
Marine mammals require two media. Whalers did not have to search the nearly
opaque depths; they only needed to wait until their quarry surfaced to breathe. Many
materials such as spilled oil collect at the land-sea interface, providing obstacles for a
number of functional groupings, including neuston, pleuston, birds that rest on the sea
surface and any underwater species that must surface to breathe. Sea turtles further add
to their vulnerability by laying eggs on land, where they must contend with destruction of
nesting beaches (for example, by the building of seawalls), egg predation (especially by
humans) and light pollution (which disorients young that hatch at night, preventing them
from reaching the sea).
20
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"&*£•£&£%£ ^dfflSS bS "^—Ptae and piams that
X De,e™,iM ts of ralnerabi|jty among sn^iflc _
X De,e™,iM ts of ralnerabi|jty among sn^iflc ^ _ ^
• d GetC ?enninants of *— among
21
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are
ecosystems of the same Knd. . omethtaf^"- ""I**™ '° other new
regune is preserved, these succ^/onal aa^tri™ g
" 'Ft*** ****
sometimes iate
coastal waters off arid regions and Ae 4t ma?ori^ of ?h ' * are ** non"uPwelling
areas) from the surface to the seabed \ J * C °pen ocean (n°™pwelling
^^ (nutrient addition
an area which has underZ ™?d £ i dischar«es and ™noft In Key
an ever-greater an^rfSfJ?^ devel°Pment ^ recent years and
** Mia
Largo, Horida, an area which has ur ™ i
which receives an ever-greater anrfSfJ? evel°Pment ^ recent years and
the north, reef corals have ^S^^^T ** Miami metr°P°Htan area to
grow faster than corals under eu^ophS foSions overgrowth *»n algae which
ds nuravb^^ « also -1— ble to anthropogenic
supported rich fisheries becal £' ^arTual S toS?™^ ??Uth °f the Nil^ Once
of nutnents. The completion of the Asm Hieh SL Pt d, ^ PredictaWe inputs
Nasser eliminated this flooding and mSSfeSS 2^ *e nutrients in Late
lakes (Shaheen and Yousef, 1979) i S land rf?SS? J6 f!?henes in the ^arine
vanous nutrients by affecting both ion eSn^n± y ?lng6S the avai^bility of
feation in soils. Acid pT&dphation^te^fP^ and the amount of mWen
altering nutrient availability the Species comPosition of an ecosystem by
than eutrophic ones, however
general principle is that BJ^^^^^ ,than ^crease it. A more '
cyclmg of nutrients can cause profound changes SS2 < -npUtS' °UtpUtS and intemal
the most important factors shaping th^ Tevoluffon^^ ?Jf etnu.tnent availability is among
of competitive interactions and^hf toSK °rganiSmS' the °UtC°me
is^ vulnerable to invasion, but
particularly vulnerable. K&l^btrt^F* T"® and glacial lakes) are
species than might oflien^S^^ *r fewer
evolutionary naivete in isolated species alSn^S the previously mentioned
-ntroduceaspe.es. ^ .-dN
22
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ttz^^zssxrisrsssz?
mountato ft ?* *? non'fi^ mammals ^^ned to isolated western
asx.-a^s"
i
f) Proximity to human populations. This is by far the most important risk factor for
23
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show litf SSSST!?8 -°?Te
-------
D THE PROXIMATE CAUSES
These ultimate causes of anthropogenically-driven biodiversity loss are manifested
in numerous proximate causes, which have been summarized here under six headings:
1. Direct population reduction (intentional and incidental taking)
Throughout most of its existence, as. a species, Homo sapiens has subsisted by
foraging for roots, fruits, insects and the occasional bonanza of a dead or dying mammal.
Technologies were-too primitive to allow early humans-to prey on healthy individuals of
the huge Pleistocene African mammalian species. Over time, an increasing
sophistication at tool-making, an ability to control fire, and an improved ability to
communicate have shifted the balance in Homo sapiens* favor.
Before the 1600s, blue bucks could be killed only by people within the range of a
cast spear. After the Dutch and their firearms arrived in-South Africa, these antelope
could be killed from much greater distances; the last blue buck was shot about 1799.
Two centuries ago, it took a team of Pacific Northwest Native Americans days to fell a
giant western red cedar, the only tree they could split for planking to make their houses.
Moving trees away from the rivers was beyond imagining. Today one lumberjack armed
with a chainsaw can down a forest giant in minutes, and powerful machines can move
and mill any tree species and ship the logs or lumber across the ocean to Japan. Our
ancestors could fish only in shallow waters^ and could take few fish at once. Today,
powerful, fossil-fueled, air-conditiojued ships electronically locate schools and harvest fish
in nets vastly larger than the mouths of the predators with which ithe fishes evolved.
There is great diversity in what humans seek from nature, how it is acquired, and
the degree to which humans restrain themselves from overexploitation. Some direct
exploitation of living things, such as the sport hunting of bighorn sheep in the western
United States, is carefully controlled and monitored. (However, see Irby et al., 1989 for
a contrary view). With notable exceptions, most industrialized countries have gained
considerable control over direct exploitation of native species. In many other nations,
however, uncontrolled taking of species is still common; populations of African elephants
are sharply decreasing throughout most of East Africa due to human desire for ivory.
Populations of black rhinoceros have been so decimated that poachers must be deterred
by round-the-clock armed guards. For many species, laws are non-existent or simply not
enforced. ;
Non- target organisms are similarly threatened. Trappers cannot ensure their traps
will snare only the intended species; a sizeable share of the organisms killed are not the
furbearers that trappers seek, but other species such as skunks and golden eagles. Now
that poaching of mountain gorillas in Rwanda has ended, the greatest immediate threat
to these endangered apes is incidental take in antelope snares set by poachers.
Perhaps more widespread is incidental take in marine ecosystems. As much as
80-99% of a shrimp-trawlers catch can be nontarget species of fishes, starfish, crabs,
stomatopod. crastaceans and jellyfish, many of which die before being thrown overboard.
25
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Shrimp trawling is a major threat to sea turtles, such as the endangered Kemp's ridley
inhabiting the coastal waters of the southeast United States (Ross et al, 1989), and a
threat of uncertain magnitude to totoaba (Cvnoscion macdonaldi)T a large, endangered
endemic fish in Mexico's Sea of Cortez (Ono et al., 1983).
Driftnets up to 30 miles long, set in the North Pacific by Japanese, South Korean
and Taiwanese salmon and squid fishermen, annually drown hundreds of thousands of
seabirds, especially.short-tailed .shearwaters and tufted puffins, in addition to thousands
of Dall porpoises and lesser numbers of other marine mammals (O'Hara et al 1986)
In the view of Jehl_(1988), the numbers of seabirds killed are indeed high and locally'
significant, but the impact of drift nets on their populations is uncertain; better answers
could be obtained through population modeling. T
Purse-seiners locate yellowfin and skipjack tunas by spotting dolphins associated
with the tuna schools. They surround the schools and unintentionally drown dolphins in
their nets. In 1972, more than 423,000 small whales of 13 species were killed, mainly
spotted, common, striped and spinner dolphins. The passage of the Marine Mammal
Protection Act and subsequent laws have sharply curbed the killing, but it is still on the
order of 20,000 for the U.S. tuna fleet alone (Jehl, 1988).1
In the Philippines, fishing methods reach unprecedented levels of destructiveness
to non-target species. Fishing boats pulverize coral reefs with heavy weights to drive out
reef fishes or collect these fishes by poisoning entire reefs with cyanide.
In recent years, the attention of conservationists has focused on other causes of
declining biological diversity. In some cases, direct taking is a humane issue or an issue
of sound resource management rather than a question of diminishing biological diversity.
For a significant number of taxa around the world, however, intentional and incidental
taking probably rank with physical habitat destruction, pollution, climatic change and
alien species as major threats.
2. Physical alteration
When Europeans first settled in North America, the first species they jeopardized
were those they killed for food, fiber or skins, and those they considered competitors.
Since then, the most jeopardized species have become those whose habitats humans
appropriate. Worldwide, in places as diverse as the tundra of Alaska's North Slope and
the rainforests of Borneo, the greatest damage to biological diversity is caused by
physical alteration of ecosystems.
Human beings physically alter ecosystems in several related ways. The most
complete kind of alteration is conversion, the complete alteration of ecosystem structure
composition and functioning. Ecosystem conversion includes the changing of virgin
1 Further decrease of incidental dolphin kill is expected following recent decisions by
the three largest U.S. tuna companies to produce "dolphin-safe" tuna.
26
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prairie into cornfields, of deciduous forest into coniferous tree plantations, and of
freshwater marsh into shopping malls. i
u „ Th4eXt!,n^£coilversion differs marke<«y from one ecosystem to the next.
Between 25 and 1 40% of the humid tropical forest biome is gone (Erwin, 1988)
Approximately 56% of former United States wetlands is gone (CEQ, 1989). Some 87%
of the ancicn4.forests in the Pacific Northwest is gone (Norse, 1990). EssentialTno
functioning North American tallgrass prairie remains; only a few scattered remnants exist
(Nature Conservancy, personal communication with Barbara Shapiro). Weedy species
have coped with tee. changes by moving to other ecosystems or adapting to the
markedly changed conditions in situ, but the specialists requiring specific habitats have
been reduced roughly in proportion to the percentage of habitat lost.
i
s/iious ^ °utriSht convera^^ One is
gflentatl°n' m ™?ch barrier? to o^nism dispersal separate more or less
' arae more or ess
intact pieces of ecosystems The interruption of a river with a dam to create a lake the
clearcut logging of parts of an ancient forest (even if replaced by a tree plantation), or
the building of a road through a salt marsh would all create barriers of this sort
' '°n haS bf*n *-l?pic Of intense scrutiny since Terborgh (1974) and
™nnt- 6gan apply1?? 1Sland Wogeog^Phy theory to fragmented remnants of
once-continuous ecosystems. Destruction reduces the area of the ecosystem, but the
nef™T8, frlgir'en,tS ^ Suffer.fl2m decreased populations and from the penetration
of external physical and biological influences. Wilcove et al. (1986 ) provide a
particularly illuminating example. Birds in isolated temperate forest fragments are
SSfh / IT0? gher 'ate ? nest Predation and brood parasitism from edge species
S? f ?^S lmeters mt° the fragment. As a result, small fragments support fewer
species of birds than would the same land area within unbroken forest.
Se,C°?d ^ °f partial alteration is *e deletion of some ecosystem component
f?10**. ecosysteP simplification. Examples of this include the removal
naT1tH t • treeVnMan anCient forest' elimination of a stream's sensitive submerged
SSSV^ t0 Jncrf al6d Sllt^i0n f^°m livestock P™**' and eagle abandonment of g
nesting trees due to human intrusion.
di^^K^T aftivitie.suthat fragment ecosystems also simplify them; the previously
discussed edge effect" contributes to this. Intact forests are moisteir, less windyf and
cooler in hot weather than clearcuts. In the Southeast, Seastedt and Crossley (1981)
bTateSeT^Vn^f^" * ^ S°fl ^f averaged 26°C V9^ ^"hin forests
but average 42 C (108 F) in adjacent clearcuts. When forests are fragmented, the
fiWrf? teiT ] c?ndltlons Penfrate the fragments, allowing hot, d;ry air to desiccate
forest plants, fungi, slugs and salamanders that require moist conditions.
OSySt^^h more three-dimensional structure sustain more species
* MacArthur, 1961). A flat expanse of rock will support, only species able
to withstand exposure to heat, cold, rain and wind, and able to deter enemies without the
aHHstanee of shelter. The addition of boulders or trees creates diverse microclimates and
27
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refuges from stress and predators. Structural diversity provides opportunities for species
that need vertical surfaces, horizontal surfaces, tangles, cavities, mating sites and
observation posts. For example, a forest having a canopy but no shrub layer cannot
support a hypothetical bird that forages in the canopy but nests in shrubs. Complex
Habitats accommodate more species because they create more ways for species to
survive*
flown SJSSW^ div*rsity begets.more diversity. In English .tree plantations, Peck
(1989) showed that ^creased tree diversity provides increased feeding opportunities for
songbirds; monocultures have the lowest diversity. Predators, too, can affect species
diversity, as Paine showed in a classic study in Puget Sound. He found that removal of a
top predator, the ocher starfish, decreases species diversity in the intertidal zone because
it allows mussels (MgihiS sp.), the dominant competitors and preferred prey of the
s arfish, to monopolize the substrate (Paine, 1966). In these and many other cases,
simplification, including reduction of species diversity, leads to a further simplification.
The differences between fragmentation or simplification and destruction are a
matter °f degree. All ecosystems have some degree of natural disturbance and occur as
mosaics of different successional stages. Most communities would persist for eons if the
nature, amount and timing of disturbances did not change dramatically. Anthropogenic
the
3. Chemical pollution and solid wastes
f16 rere t0 I a b°ttle of sterile nutrient broth and seed * from a pure
rtU Pir°f *** Sf M Eaatemfiffl. the population would begin to grow rapidly.
I« «r I '< ^ • ™Uld £VC1 °ff and finally reverse into dedi"e> Pe*>aPS to a low
level or perhaps to extinction. The Tetrahymena would unwittingly have exhausted then-
food supply and poisoned themselves with their own toxic waste products.
Of course, this artificially simplified system lacks renewable resources and
supplementary species to convert waste products into harmless or useful substances. In
nature, .Tetrahymena are normally part of a self-regulating system. If they overexploit
w^efbeS^611" P^^^ decfease a"owing their prey to recover. IncTeSng
™£r,w £ 7s?*? ^ot^r species capable of metabolizing them and thereby
rendering them safe for Tetrahvmena. In short, Tetrahvmena have survived because thev
rd SyStem °f indefinitely renewable food supplies and indefinitely recyclable waste
products
Wnmn SfJ6*?^6™ eXTple holds tme for "^ population of organisms, including
HpmpMpienE. ,In the past, human waste products were resources for animals, plants
and microorganisms, which converted them into usable resources, but the wastes of
modern society tend to be regarded as pollutants to be removed or dispersed The
of was{fs generated ^ a still growing and increasingly "disposable" society have
overwhelming proportions in many industrialized nations, and the problem of
-------
a) Acid deposition. |
b) Gaseous phytotoxicants (e.g. ozone).
stress (EPA, 1987). y warmnSthat a forest ecosystem is under
29
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c) Excessive nutrients.
Nutrients are considered a major hazard to unbuffered lakes, a lesser threat to
buffered lakes and unbuffered streams, and still less of a threat to buffered streams.
Nutrients have the potential to cause major problems in estuaries and moderate
problems in coastal waters (EPA, 1987).
. .In freshwater ecosystems, lakes, rivers, and streams, degradation most commonly
takes the form of nutrient overloading. Run-off from farmlands and discharges from
wastewater treatment facilities (or other point sources) can inject nitrogen and
phosphorus into waterways, stimulating excessive and sometimes noxious growth of algae.
when the algae die, after exhausting the nutrient supply or from simple overshading,
their products of decay remove oxygen from the water and cause suffocation of fish and
other aquatic animals. The technical term for such unwelcome enrichment is
"eutrophication". Fish, insects, and submerged aquatic vegetation (and other primary
producers) may be threatened by accelerated eutrophication in freshwater ecosystems.
Estuaries are especially vulnerable to eutrophication. At the interface between
-•freshwater and marine systems, estuaries trap nutrients that contribute to their high
productivity but can cause eutrophication. Receiving the outflow of entire watersheds
and nearby cities, the estuaries may be victims of toxic loading as well. In areas where
human waste and other organic material are dumped directly into waterways, the threat
to human health is obvious but there is also the danger that aquatic organisms will be
killed by the oxygen demand of the waste (as is the case with the algal die-offs
mentioned above). Fish, shellfish, and many other groups in the estuarine community
may be seriously reduced by nutrients and related pollutants. Seagrass and coral reef
communities are very seriously threatened by excessive nutrient and organic loading. It
is also possible that a connection exists between nutrient discharges and blooms of
noxious red or brown algae. These "red tides" seem to be increasing in many coastal
areas and could also be benefitting from global wanning (Brower, 1989).
The oligotrophic (nutrient-poor) characteristic of coral reefs is easily upset by
enrichment from sewage or runoff from fertilized agriculture. Discharge of sewage into
Kaneohe Bay, Hawaii has dramatically changed the rocky benthos from a coral reef
ecosystem to one dominated by green filamentous algae (Steven Smith, University of
Hawaii; personal communication). The addition of limiting nutrients favors both
phytoplankton blooms, which lower benthic light levels, and fast-growing soft algae
which smother and shade out corals.
d) Pesticides.
Pesticides or herbicides applied in freshwater or estuarine ecosystems 'could have
high ecological impacts but effects in wetlands are uncertain. Also uncertain are the
effects of biocides (substances destructive to many organisms) applied in terrestrial
ecosystems on those ecosystems or nearby aquatic ecosystems. Pesticides can, however,
have major impacts on biological diversity in agroecosystems, reducing the abundance of
many beneficial insects and other non-target organisms (EPA, 1987). -The repeated
application of pesticides selects out unresistant strains of pests.
30
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Pesticides can vary widely in toxicity, specificity, persistence and bioaccumulation
Pesticides which lack specificity can have harmful effects on a wide range of target and
non-target organisms, and can decimate populations of a "pest's" natural predators.
Though the use of some pesticides which are highly toxic to wildlife has been banned in
•fjii (6A*l9flSU™y by the Fish and Wildlife Service (FWS) identified 85 of the
nations 430 National Wildlife Refuges as potentially contaminated by agricultural
dramwater or by municipal, industrial or military activities. Investigation of the Refuge
System, the only federal lands managed primarily for wildlife, was sparked by the
discovery of chemical contamination in the Kesterson Refuge, which caused the death of
Sfic°f Ttely •1'000 ducks between 1983 and 1985. A 1987 GAO report indicated that
FWS had not adequately investigated the issue, and that contamination may be even
more widespread than FWS reported. (GAO, 1987).
31
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ataospteic cha,8e (climate, W.B and
sssea.
32
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Third, warming will have major consequences for the hydrclogical cycle.
Unquestionably, wanning will cause earlier snowmelt and a smaller proportion of
precipitation falling as snow, which (unless there is higher rainfall) will mean lower
streamflow in summer and fall, when human and biological demand for water is highest
(Norse, 1990). Wanning will increase evapotranspiration by plants, causing ecosystems
to become drier unless there are large offsetting increases in rainfall. Warming will
cause higher cloud cover over much of the planet and higher- rainfall in some areas.
However, general circulation models tend to predict that much of the increased rain is
likely to fall over the sea, and some models predict that midcontinental areas will get
less precipitation.-So, some land areas will become wetter and some will become drier.
The effects of increased dryness on the propagation of wildfires, a major determinant of
many natural community patterns, and on outbreaks of disease organisms, merits special
attention.
i
The threat of increased UV-B radiation caused by stratospheric ozone depletion is
less certain. Although the course of increase in UV-B is much eiisier to predict than the
course of climatic changes, the effects of such changes are much less certain. Studies of
the effects of climate on the biota date back more than a century, while studies of UV-B
are mostly very recent and incomplete. It is known that UV-B affects DNA synthesis,
damages immune systems, increases skin cancers and causes cataracts in mammals. It is
further known that UV-B disrupts marine planktonic communities (Worrest and Grant,
1989) and affects some tree seedlings (Sullivan and Teramura, 1988). The magnitude of
these effects on populations, species and ecosystems is still hard to predict.
Unlike some other trace gases involved in global change, carbon dioxide has
direct physiological effects on plants. At first glance, these effects appear beneficial.
CO2 is essential for photosynthesis and may limit plant growth; increasing its
concentration increases growth rates in many plants, an effect called "CO2 fertilization."
CO2 also benefits plants' water relations. Plants take in CO2 through open stomata,
which also allows water loss (transpiration). At higher CO2 concentrations, plants can
keep more stomata closed, and therefore lose less water. Thus, increasing 'atmospheric
CO2 diminishes drought stress. j
Plants using the two different major pathways of carbon fixation differ in their
response to increased CO2 levels. "CJ plants benefit more from enhanced CO2
conditions than "C4" plants (which constitute a small fraction of temperate species but a
large fraction of tropical and desert species). Further, as Fajer (1989) notes, the
magnitude of CO2 growth enhancement in C3 plants is species-specific. Thus, increasing
CO2 will alter competitive interactions between plant species. It is possible that many C4
plants will become rarer or extinct and that there will be large changes in abundances of
€3 plants in the next century, which could have important consequences for food webs,
community structure and ecosystem processes such as nitrogen fixation and soil
formation. Species that we consider "weeds" could dramatically increase in abundance,
stimulating increased efforts at control.
«
Additional complications could further affect biological diversity. CO2 enrichment
decreases the nitrogen content of plant tissues*.prompting herbivorous insects to respond
33
-------
in several ways. Lincoln et al. (1984) found that tested larvae increased their feeding
rates, indicating that "...the increased levels of plant productivity at higher CO2
concentrations may be offset by higher herbivory and could even be reduced below
current levels." Lincoln's more recent research on four other herbivorous insects and
their hosts has consistently found increased feeding rates. But Fajer et al. (1989) found
increased mortality in early larval instars of one species feeding on foliage grown under
enhanced CO2 conditions (and thus having decreased nitrogen content). This indicates
that herbivorous insects could become less abundant, with effects including reduced
abundances of insect-feeders.
5. Alien species \
How does the addition of alien species affect biological diversity? Each case is
different, but some generalizations can be made. It is clear that organisms evolve not
only in response to their physical environment and to members of their own species, but
in response to other species as well. This 'coevolution between hosts and parasites,
predators and prey, and between mutualists means that the biological fabric of a
community is distinctly interwoven; it is not just a random collection of threads. Species
interact in myriad ways that we are only beginning to discover.
Alternatively, it is clear that communities generally have some "slack"; ecosystems
are not so tightly organized that they cannot accommodate some compositional changes.
Paleoecology shows that current assemblages of species did not exist in the recent
geological past; some species that coexisted in the late Pleistocene are now allopatric
(their ranges do not overlap) (Graham, 1986).
When a species is introduced into a new area, the alien species generally
disappears. Sometimes, however, the alien species survives and proliferates in its new
niche. This is particularly common in areas with "naive biotas" such as islands (e.g.,
Hawaii) (Vitousek, 1986) or areas that are now "undersaturated" as a result of previous
climatic changes (e.g., southern Florida) (Courtenay, 1978). Not having evolved in these
ecosystems, and thus being much less vulnerable to indigenous predators, parasites and
competitors that have evolved no ways of dealing with them, alien species, are sometimes
able to proliferate to the point that they disrupt existing communities.
•Rabbits (Oryctolagus cuniculus) introduced from Europe overwhelmed Australia;
Australian Melaleuca thickets are overrunning Florida; white-tailed deer from the United
States are wreaking havoc in New Zealand, and so on. Every organismic biologist can
provide many examples of how introduced species have adversely affected native biotas,
profoundly changing ecosystem dynamics and causing extinctions.
The problem is not limited to the land. As with many freshwater fish
communities, those of the Great Lakes have been irrevocably changed by the
introduction of alien species, in this case, predatory sea lampreys and planktivorous
alewives (Alosa pseudoharengus). Although alien species in marine ecosystems have
attracted much less .attention, there is now excellent research showing their importance
in undersaturated ecosystems such as Coos Bay, Oregon (for example see Carlton, 1989).
34
-------
6. Interactions
35
-------
betweeS^ * the impending interaction
major threat affecting a large percenfLf n^F ,±- Dentation. Alone, each is a
fragmentation wfll reduce the ffiSS^S^St"1^™ T°gether' habitat
Man-made barriers to migration Sdude mfd? ^iP0*** in response to climate chan
3"
e t '
Man-made barriers to migration Sdude mfd? ^iP0*** in response to climate change.
demarcating wildlife refuges L Wi!cox (1980) nmes.38" ^ ^ ** Static bord*rs
s^-ssSSSF^f-'-s'a.'-
P "'Adapted to a novel clim
extinction results "apted to a novel climatic regime-and
Speaes ™,h small la^dinal ranges «** " ^ endl
ens (Nope'
already have higher UV-B lev^but dSon nf tT™ dep etlon'' h«her elevations
beyond what previous refugeesll fte rntnSns l^nS. ^ ^ fa™~ W
rnn^^^
such interactions by noting: * ' summarized the importance of
36
-------
E THE MAGNITUDE OF THE THREAT
1. Overview
select group of ecologists could be ^eyeTa, Sne Sure daS T" ** '
It is recogmzing ,ha,, wW e
species, communities and
some «hr,ho,d beyond
f* °f *eSe StreSSOrS^
s.ressors beneflt some
of
Schindler and coauthors
measures of population health are valuabk
redundancy in ecosystems i
productionlcan 2K
dramatically changed species composMon
indicators of biological
.'
species composition and
of stress because the functional
37
-------
groups *wn is weighted heavily towards
example, there are categories for several SJnfn ^ "&«"«* are possible. For
best-studied organisms, lid cleS pStel iave "2 Sg f llds,of. bird*; birds are the
some stressors On the other hand h^a emerged about their vulnerability to
r an a
insects; undoubtedly flyin eiS soil I^^Sf ^ different
stressors. Bacteria were no^ ^cludTd * re.sPonse to
cludd du to ack rfi .nse to ™ny
of
In
sd organisms~viaT"T-1VC U""1^" reiei? tO deliberate ^Hing and
hnt"nnt inrrrr,v>~ nT -j , ®* ^PPing, animal damage control fkhina a«^
uui noi logging. Incidental takinp" re*ff* +1* • *«^«uv»i, u»uing, ana «»».
organisms because of the above activities • Thv!f Umjlten(jed.ki11ing of non-target
shrimp trawl is a victim of incidental taldna »Ph • i ^ "d y,,Sea turtle drowned in a
category, in that it includes simnlifirflt;™ SL Jl *^7 alteration is the most inclusive
'for timber, agriculture minerals housinp' fragment.at.lon and destruction of ecosystems
might be useful for this category' to be hmS^SS • f1 mdus,tnal development. It
ruture efforts to refine this methodology SeV6ral Separate categories in
TMnrtStdS^^ to kill living organisms.
pesticides) into streams, rivers ^ lakes a?d the ^ ^ g$ ** taricarts (including
causes of eutrophication, mSnly fa ^SfcSSi. "M^™^ indudes **
garbage. "Conventional air pollutants" inSiuK!™' • Sohd7afles refers to nontoxic
carbon monoxide, ozone^ScX^TO^^tn^'S611' ^ ?itr°gen °xides'
wastes. Whfle this list of stressors is cenS n f ^ • f ^liberate disposal of nuclear
represented.2 K certainty not all mclusive, most major stressors are
four sym on S'jfflS "* "?•" fe "" ^ one of
a substantial impact that merit? study £?& b^^ '%£TfL * half-fille"
•sa very serious area, tba. deservesUeS
o^ ™-« - «**» due to
is significant in some cases (eg manatee? hit h?h * categones is not considered, but
of this report should include^chTcc Mfl^KSfi?^ 7«F C^' UPdates
is unclear whether accidental spills of ha^rdnm tnf, t incidental taking." Second, it
assessment of risk from
38
-------
mark indicates that there is net enough information to make a reasonable judgment, or
that the available information leads to conflicting conclusions. A question mark in
addition to a symbol indicates the rating is less certain. i
i
I
2. Status of the best-known taxon: Birds3
i
Taxonomic groups of living organisms differ so greatly that none is truly
representative of all groups. Still, better data exists for some groups and can provide
limited indications-for application to other taxa. Birds have been studied more
extensively than any other group, due in part to their colorful and conspicuous nature.
Virtually all bird species have now been scientifically described, and many thousands of
scientists and birdwatchers observe them in both developed and developing countries.
Despite their importance in ecosystem functioning, the same cannot be said of plants,
fungi, fishes or mites.
•, '
Data on bird populations in the United States are maintained by the Fish and
Wildlife Service (FWS). Certain species (such as waterfowl) have been systematically
monitored; songbird populations have been assessed since 1965 in the FWS-coordinated
breeding bird surveys; and wintering populations have been counted since 1900 in the
National Audubon Society Christmas bird census. Despite these efforts, there is no
central repository of population data, the quality of the data are highly variable, and the
taxonomic distribution of data collection is uneven. Documenting general trends is
extremely difficult and nothing better than educated guesses are available for many
groups of species (Jehl, 1986). Jehl's chapter in the Council on Environmental Quality's
1986 Annual Report summarizes status and trends of the birdlife of the United States.
International data have been more generally summarized for rare birds by the
International Council for Bird Preservation. j
The following summary presents information on major groups of birds, first in the
United States, and second, internationally. As Jehl noted, some 70% of the 1000-1350
bird species occurring in the United States spend at least part of their annual cycle
outside the United States (Jehl, 1986). His paper is the basic reference for all data not
otherwise attributed.
a) Seabirds. The total seabird population in North America and aidjacent oceans
approximates some 100 million birds of 106 breeding species. Tens of millions of
southern hemisphere breeders spend time north of the Equator. >Vhile population status
is unknown for at least 75% of these species, some trends are appiarent. Scavenging
commensals of humans (gulls and fulmars) are thriving. Terns are declining, due to
competition with gulls and with humans for nesting habitat. Some fish-eaters (pelicans
and cormorants) are showing recovery from pesticide-induced declines. In general,
North American seabirds appear to have been stable or increasing over the past few
decades. Greatest threats are to temperate and tropical nesters whose habitats are being
lost to disturbance by humans, including development on beaches where the birds nest.
^This section was primarily written by avian ecologist David E,! Blockstein.
39
-------
Other threats include entanglement in drift nets and ingestion of plastic and other
debris. Entanglement rates are high, but may not reduce overall populations. Local
impacts are very significant, however, in areas with much driftnet fishing (such as the
North Pacific) and in the North Atlantic, where entanglement occurs with conventional
nets. Ingestion of large amounts of plastic has been documented in many species of
seabirds. Present rates and amounts of ingested plastic are too small to have effects on
most species. Certain populations that have been well studied, such as albatrosses in
Hawaii, show chick mortality due to plastics.
b) Waterfowl. Data on waterfowl are as good as on any group. The FWS
documented a continuing overall decline in duck populations in North America since
monitoring began in 1955. Populations are presently at their lowest level since that time.
Populations of mid-continental breeders, which include more than 50% of North
American waterfowl, are in critical declines. This is largely due to habitat destruction of
wetland breeding areas, such as marshes and potholes, to accommodate agriculture. The
recent drought has exacerbated this situation to the point where hunting has been
restricted. A 15-year multi-million dollar North American Waterfowl Management Plan
has been approved by Congress to purchase breeding and wintering habitat.
Populations of geese, which generally nest in the tundra, are mostly stable. The
exception are geese who nest in western Alaska, where overhunting by sport and native
subsistence hunters is depleting populations. Loons have decreased throughout the
century, largely due to disturbance on their northern nesting grounds. Some range
expansion has occurred recently. However, acid rain and interactions with mercury
pollution may have significant effects that are just being investigated in these fish-eaters.
c) Colonial wading birds. The 16 U.S. species of wading birds are highly dependent on
wetlands. Recently, some good monitoring has been done by ornithologists from FWS
and other groups. By the 1970s, ranges had been recovered from feather trade
depletions of 1880-1900, which nearly eliminated many species (and led to the formation
of the National Audubon Society). Total numbers are still reduced. Overall most
populations have remained relatively stable, except wood storks, which are now
endangered, and cattle egrets, which are self-introduced from Africa and are increasing
exponentially. Local declines are most serious in California and southern Florida, where
there has been almost total collapse of a wading population that once numbered in the
hundreds of thousands (Ogden, 1987). Habitat loss due to wetland conversion is a key
stressor as are harmful water management practices. Pesticides and irrigation practices
have had significant local impacts.
Unless wetland conversion is reversed, significant declines are expected in this
group.
d) Raptors. Six of the 50 raptor species breeding in the United States are endangered.
Most populations have increased from historic lows caused by shooting,.human
disturbance and development, and DDT and other pesticides. Despite recovery, they
generally remain below historic levels. Bald eagles and peregrine falcons have recovered
40
-------
41
-------
Most shorebirds breed in the Arctic tundra. Thus, they and other tundra
groundnesters (geese and songbirds) are extremely vulnerable to global warming. If
projections that wanning will be most severe at the polar regions are realized, shorebirds
will suffer critical declines because their nesting areas will be flooded.
7
g) Songbirds. Approximately 50% of the North American avion species are small
landbirds. Most nest in woodlands and a smaller percentage nest in fields and
grasslands. Population trends come from breeding bird surveys (BBS) since 1965 and a
few long-term or multi-site studies of forest-dwelling birds. Most of these birds are
migratory, many (especially forest-interior songbirds) wintering in the neotropics.
}
Grassland birds are generally declining. This is especially true in the East where
farms and pastures revert to s icondary forest. As much of the East was once forested,
these declines may represent a return towards pre-settlement conditions. Riparian
breeders are of special concern in the West, especially in California, due to habitat
destruction and loss of streamflow to irrigation.
A major summary of population declines in migratory birds in eastern North
America has just been published (Askins et al, 1990). It summarizes data showing
severe and catastrophic declines in some species of forest birds in the United States
since monitoring began in the 1940's and 1950's. Most of these declines are of
neotropical migrants inhabiting forest interiors.
Long-term studies in small urban and suburban forest preserves show declines in
interior species, but not in more resident edge-dwelling species. These changes may be
due to local impacts related to forest fragmentation and the edge effect or to destruction
of wintering habitat.
Data are inconsistent in the few long-term studies of extensive (> 1000 ha) forest
tracts. Declines in migrants, where they occurred, have not been as severe as in small
forests. Some changes may be related to habitat change as the forests mature.
Many neotropical migrants have lower densities in small forests than in large
forests and some species tend to be absent from small forests. Experimental and
observational evidence show that open-cup nesting species (most neotropical migrants)
have low reproduction in forest patches due to nest predation by edge-living species and
brood parasitism by brown-headed cowbirds (also an edge species).
In tropical wintering areas, many species of forest-dwelling migrants have much
higher densities in secondary and mature forests than in early successional stages. Most
migrants winter in the Caribbean basin, where deforestation trends foretell major
population declines.
Breeding Bird Survey data show that most neotropical migrants have declined
during the past 11 years following a period of stable or increasing populations during the
late 1960s and '70s. Absolute declines and declines in rate of population increase are
almost restricted to species that are concentrated in forests during the winter, even those
42
-------
that nest in early successional habitats during the summer. This may constitute the first
unambiguous evidence of dechnes in populations of neotropical migrants due to the
destruction of winter habitats (data analysis by Russ Greenberg).
frao™^-5' declin,es [n Potations of forest:dwelling songbirds sire due to habitat
fragmentation on the breeding grounds and habitat destruction on the wintering grounds-
reversed my> TheSC tod8'are in Seri°US trouW^nless present trenTare
There has been little quantitative study of forest birds in the West.
S^land !?dS- ^ esj™ated 93% of all species and subspecies of birds that have
become extinct since 1600 were island natives (King, 1978).
Hawaii: The Hawaiian Islands boast the highest percentage of endemic flora and
w^wSK?* Polynesr arrivfd' there were some "S^S
forests fnd ? d t- 7>fre.SUb? qU6ntly exterminated due to destruction of lowland
forests, and predation and habitat destruction by dogs, rats and pips Thirteen additiona
species have gone extinct since the arrival of Europeans in 1778^0^^37^
of native land birds remain. Some 24 of these (65%) are endangered, a 1 buf 3 of which
are endemic; six species number fewer than 50 individuals.
K^ •T^e^?ltur.e for re.maining native species of Hawaii appears bleak, as the stresses to
biologica diversity continue unabated. Deforestation for lodging and d^velopmenr
and s±d of a"5' J' eral ^ alien,mammals' mtroductionValfen
°f WWch m
an s o a ' ,
aS comfnue S ^f^^ °f WWch m transmitted ^ introduced mosquitoe )
^ entm Spedes from ^cupying otherwise
a comnue uoe
suitaWe SSiiSftS^ ^ ^^ PTent!-many Spedes from ^cupying otherwise
I £ J * * • ?' Some species of seabirds and waterbirds are also at risk due to
habitat destruction and disturbance by introduced species. j
n ;hi;g HEy ter-e T 18 Species of birds on G™™. 12 of which were landbirds
S^^^JSTJ J^f on of the Solomon Is]and brown tree snake dtnrds
S«S A if ^ la ^ ?1S b,ird" and llzard-eatinS snake has paralleled the decline of
forest-dwelling birds. As of 1987, 7 species or subspecies of landbirds were extinct and 4
6 Vef °fenction' ^ oulations num
^ Vef^ °uf.e^nction' ^ Populations numbering less thano
n .nt K M£ronesian kingfishers and Guam rails have been removed and axe thriving
^ raflS ^ be reintroduced - an oment on the""'
?u & r extermination of an entire avifauna by a snake Is unique The
of other factors such as deforestation have not been assessed. One of the
lTat,ZTgJarge traCtS °U°reSt " Slated for destruction by the Navy in ordlr to build
a satellite tracking station. This area would be a site for reproduction if the snake CM
be controlled Plans are presently under review by the FWS. The rown tree snaklaTd
o her species have been discovered on other Pacific islands (including ^^waln a^a result
of inadvertent transport with cargo. Whether the history of Guam wiV be repeated
elsewhere may depend upon local conditions. repeated
43
-------
SffiS^'SSSffiS^]'* ta «*•"*• According ,„ the
&*^*'stttt&ttz
area. i' ' tonomic8ro<'P """ in
other continuous habitats
y ha«-,- •
birds as well as other spedes! "^ W1" resu" m tremendous extinction of
A
sncav affr, or
such as guans and galliformes^nd^n^,?T ?°me species- P^'cularly la
migrating . songbirds8 and r^S^ •»" w^birds. of
Competition from alien species is^nlfcanMn Sml y "^ the Me«'^anean.
Global warming would have its greS ta ' « " e <^es. Particularly on islands.
coasta, habita.. Shorebirds '<
uncomSou' ^Sy StatSrt^l* llT '° "^ Spedes' A -*-.'te
developing world.Ppollmfon0fau^yaSd water n^v'h are-S'm """flj"^ m mu'ch of the
Direct exploitation for food sfenfficSav aff?r,?f "" ™Portai« factor in some areas
such as guans and galliformes^nd^n^,?T ?°me species- P^'cularly large birds
migrating . songbirds8 and r^S^ •»" w^birds. WSSL of
Cometition fro y " the Me
mobfle enough to
of fte birds of the world loo *£££*& j^ * •» to'
IV Conclusion
is clear to%^0p^to2,SSJS^J?t® I???1 race.with a Painful dilemma. It
emnrnnmaA* ^—I -Lt-jT .. """icuuilg mOmentOUS IS hann^nincv +« *U !_!._!, l
a panul dfle
; m
opportunity will be lost. beneflt of humans' must be made now or the
44
-------
V TABLES
45
-------
Table 1. Three kinds of global atmospheric change affecting
biological diversity.
Global climate
Increased UV-B
Increased CO..
Causes
Fossil fuels
Land use
Manufacturing
Manufacturing
Fossil fuels
'i Land use
Trace gases
CO2, CFCs,
Methane,
Nitrous oxide
CFCs, Halons,
Light chlorinated
hydrocarbons
CO,
Understanding of
physical effects
Low
Medium
High
Understanding of
biological effects
Medium
Low
Low
Likely impact on
biodiversity in
50 years
High
Medium
Medium
Likely impact on
biodiversity in
100 years
Very high
Medium
High
46
-------
'hreats to Biological Diversity o Minor impact
itigUOUS 43 States O Substantial impact
Of3 • Very serious threat
? Lack of or conflicting information
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VI LITERATURE CITED
Allen, J.M. 1963. The Nature of Biological Diversity. McGraw-Hill Book Company.
Askins, R.A., Lynch, J.F., and R. Greenberg. 1990. Population declines in migratory birds
in eastern North America. Current Ornithology 7:1-57.
Barton, K. 1987. Bureau of Land Management. Pages 3-59 in R.L. DiSilvestro, ed.
Audubon Wildlife Report 1987. Academic Press,,Inc., Orlando, FL.
Barton, K. and W. Fosburgh. 1986. The U.S. Forest Service. Pages 1-156 in R.L.
DiSilvestro, ed. Audubon Wildlife Report 1986. National Audubon Society, New
York, NY.
! „
Booth, W. 1989. Frogs, toads vanishing across much of the world. The Washington Post
12/13/89 p.Al.
Broecker, W.S. 1989. Greenhouse surprises. Pages 196-209 in D.E. Abrahamson, ed., The
Challenge of Global Warming. Island Press, Washington, DC.
Brower, K. 1989. State of the reef. Audubon 89(3): 56-81.
Brown, J.H. 1971. Mammals on mountaintops: nonequilibrium insular biogeography.
American Naturalist 105:467-478.
Cade, T. J. 1983. Hybridization and gene exchange among birds in relation to
conservation. Pages 288-309 in CM. Schonewald-Cox et al., eds., Genetics and
Conservation. A Reference for Managing Wild Animal and Plant Populations.
Benjamin/Cummings Publishing Company, Inc., Menlo Park, CA.
Campbell, F.T. 1988. The desert tortoise. Pages 566-581 in W.J. Chandler, ed., Audubon
Wildlife Report 1988/1989. Academic Press, Inc., San Diego, CA.
Carlton, J.T. 1989. Man's role in changing the face of the Ocean: Biological invasions
and implications for conservation of nearshore environments. Conservation
Biology 3(3):265-273.
Carson, R. 1962. Silent Spring. Houghton Mifflin Company, Boston, MA.
Chandler, WJ. 1985. The U.S. Fish and Wildlife Service. Pages 1-24 in R.L. DiSilvestro,
ed. Audubon Wildlife Report 1985. National Audubon Society, New York, NY.
Cody, M.L. 1986. Diversity, rarity, and conservation in Mediterranean-climate regions.
Pages 122-152 in M.E. Soule, ed., Conservation Biologv-The Science of Scarcity
and Diversity. Sinauer Associates, Sunderland, MA.
50
-------
^
* DC*
. :u.S. Govern,
Washington, DC
Daniels, S. I9F9. Uninvited guests. Organic r,»r^f Aprfl 1989:
< T"* a*es *7-252
il on Environmental Quali|y,
D' 1981' SMDoomsday Book of Anim.K Viking Press, New York NY
^
-
WiM A"i°"' inrtriqm r! . .?. n ^"nsp'1"'"a!LA Referent fg
me., Menb Pari^ cl ' '' ' ....... Be«J™in/Oammings Publishing
Pages J52-163 in
Referent fg
plenly and
RUfc A
51
-------
Erwin, T.L. 1988. 'The tropical forest canopy: the heart of biotic diversity." Pages 123-
izy in t.O. Wilson, ed., Biodiversity. National Academy Press, Washington, DC.
Fajer, E.D. 1989. How enriched carbon dioxide environments may alter biotic systems
even in the absence of climatic change. Conservation Rinlngy 3(3):318-320.
Fajer, ED., M D. Bowers and F.A. Bazzaz. 1989. The effects of enriched carbon dioxide
atmospheres on plant-insect herbivore interactions. Science 243:1198-1200.
'V' *** "^ T'RRich- 1989' 3i^J5sLBfifik. Doubleday,
E. Souk. 1981. Conservation and F,vo1ntion. Cambridge University
Franklin, I JR. 1980. Evolutionary change in small populations. Pages 135-149 in M E
boule and.B.A. Wilcox, eds., Conservation Biolopv-ar. F.vnlntion.ry.p^^H;^'
Perspective. Smauer Associates, Sunderland, MA.
Franklin, J F. and R.T.T. Forman. 1987. Creating landscape patterns by forest cutting-
Geological consequences and principles. Landscape Fmlngy 1(1):5-18.
Fuller, E. 1987. Extinct Birds. Facts on File Publications, New York, NY.
General Accounting Office. 1987. Wildlife Manflr.ment-Natinna1 ^^Contaminati
K Difficult to Confirm and Clean Tip n.v r;Ar> vx/ocMngton, PC. TT1TT11Tinn
T^ Wildlife Refuges-rnntinninp Problerns
Uses Call For Bold Artion ITS OA'O Wn^nin£toj DC.
Graham, R.W. 1986. Plant-animal interactions and Pleistocene extinctions. Pages 131-
154 in U.K. Elliott, ed., Dynamics of Fytinrtinn john Wiley & Sons, New York.
Irby, L.R, J.E. Swenson and S.T. Stewart. 1989. Two views of the impacts of poaching on
YeU°WSt0ne Vall6y' ^^ US^ ^^
Jehl, J.R Jr 1988 Birdlife of the United States. Pages 1-64 in The Seventeenth
U'S- Government /rinting
" Acta XXW Tnterr,
Kurten, B. 1988. Before the Indians. Columbia University Press, New York, NY.
52
-------
Low, R.
ington, DC.
leS
'$&*»££&£*£»*•
»ii »•» —
Marshall, D.B.
j*nd B.D.
^de^ ft^^S^
53
-------
TO«>** *•**.** XT •. _ ___ **
rraeger, New York, NY.
Norse, E^. 1990. Ancient For*sf, of ,h, P^jfj,
. Island Press, Washington,
Noss-
Noss>
A
for monitoring biodiversity: A hi
Coneress of th* I I.M.M .,,,., K ™g""nin Binlnnir^l Divrrnic
Congress of the United States, Office of Technology Assessment, Washington,
Ogden, J.C. 1987. Florida Region. American Birds 41:272-274.
°'^^^A^^\^^^^^^^^^^
to
birds in forest
"""
Effe« - Nature Reserve,-
54
-------
Kmentel , D., E. Garnick, A. Berkowitz, S. Jacobscn, S. Napolitaho, P. Black, S.
Valdes-Cogliano, B. Vinzant, E. Hudes and S. Littman. 1980. Environmental
Quality and Natural Biota. BioScience 30:750-755.
Power G. and 1 J. Gregoire. 1978. Predation by freshwater seals on the fish community of
Sf? ' QuebeC' Joumal Qf the Fisherv Research Board of Canada
Rabinowitz, D., S. Cairns and T. Dillon. 1986. Seven forms of rarity and their frequency
m the flora-of the British Isles. Pages 182-204 in:M.E. Souiie, ed., Conservation
J3iology-The Science of Scarcity and Diversity. Sinauer Associates, S^inderland,
Rabinowitz, D., J.K. Rapp and P.M. DJcon. 1984. Competitive abilities of sparse grass
species: means of persistence or cause of abundance. Ecology 65(4):1144-1154.
Reid, W.V. and K.R. Miller. 1989. Keeping Options Alive-The Scientific Basis fnr
Conserving Biodiversity. World Resources Institute, Washington, DC.
Root, M. 1990. Biological monitors of pollution. BioScience 40(2):83-86.
Ross, IP S. Beavers, D. Mundell and M. Airth-Kindree. 1989. The^Status of Kemn's
Ridley.. Center for Marine Conservation, Washington, DC.
Schindler, D.W K.H. Mills, D.F. Malley, D.L. Findlay, J.A. Shearer, I.J. Davies, M.A.
Turner, G.A. Lmsey and D.R. Cnifkshank. 1985. Long-term ecosystem stress: The
Sfo,^ of xvears of experimental acidification on a small lake. Science
228(4706): 1395- 1401.
Schonewald-Cox, CM., S.M. Chambers, B. MacBryde and W.L. Thomas, eds 1983
Genetics and Conservation. A Reference for Manapinp wild A^al and P1'ant
Populations. Benjamin/ Cummings Publishing Company, Inc., Menlo Park, CA.
Schreiber, R.K. and J.R. Newman. 1988. Acid precipitation effects on forest habitats-
Implications for wildlife. Conservation Biology 2(3):249-259.
Scott, J M .and JL Sincock. 1985. Hawaiian birds. Pages 548-562 in R.L. DiSilvestro, ed.,
Audubon Wildlife Report 1QSS National Audubon Society, New York, NY.
Seastedt, T.R. and D.A. Crossley. 1981. Microarthropod response following cable loegine
and clear-cutting m the Southern Appalachians. Ecology 62(1):126-135.
Shabecoff, 1988. Pollution is blamed for killing whales in St. Lawrence. New York
, p. Cl.
Shaffer M.L. and KA Saterson. 1987. The biological diversity program* of the U S
Agency for International Development. Conservation Binlngy l(4):280-283.
55
-------
Shaheen, AH. and S.F. Yosef. 1979. The effect of the cessation of Nile flood on the
fishery of Lake Manzala, Egypt. Archiv fur Hvdrobiologie 85(2): 166-191.
Soule, M.E. and KA. Kohm. 1989. Research Priorities for Conservation Biology. Island
Press, Washington, DC.
Soule, M.E. and B.A. Wilcox, eds...!980. Conservation Biologv-an Evolution?™.
Ecological Perspective. Sinauer Associates, Sunderland, MA.
~ »
Stone, W.B. and J.C. Okoniewski. 1988. Organochlorine pesticide-related moVtalities of
. raptors and other birds in New York, 1982-1986. Pages 429-438 in TJ. Cade et al
eas., Peregrine Falcon Populations: Their Management and Recovery. The
Peregrine Fund, Inc., Boise, ID.
Stouffer, R J., S. Manabe and K. Bryan. 1989. Interhemispheric asymmetry in climate
response to a gradual increase of atmospheric CO2. Nature 342:660-662.
Sullivan, J.H. and A.H. Teramura. 1988. Effects of ultraviolet-B irradiation on seedling
growth in the Pinaceae. American Journal of Botany 75(2):225-230.
Takekawa, J.E. and S.R. Beissinger. 1989. Cyclic drought, dispersal, and the conservation
of the snail kite in Florida: Lessons in critical habitat. Conservation Biology
Terborgh, J. 1974. Preservation of natural diversity: the problem of extinction-prone
species. BioScience 24:715-722.
Terborgh, J. and B. Winter. 1980. Some causes of extinction. Pages 119-133 in M.E.
Soule and B.A. Wilcox, eds., Conservation Biologv-an EvoIutionarv-FpnlngiV^
Perspective. Sinauer Associates, Sunderland, MA.
Thomas, J.W. and L.D. Bryant. 1987. The elk. Pages 494-507 in R.L. DiSilvestro, ed.,
Audubon Wildlife Report 1987. Academic Press, Inc., Orlando, FL.
Vitousek,' P.M. 1986. Diversity and biological invasions of oceanic islands. Pages 181-189
in E.O. Wilson, ed., Biodiversity. National Academy Press, Washington, DC.
Westman, W.E. 1990. Managing for biodiversity. BioScience 40(l):26-33.
Wilcove, D.S. 1988. National Forests: Policies for the Future, volume 2. Protecting
Biological Diversity. The Wilrtemgcc gn^ty Washington, DC. -
Wilcove, D.S., C.H. McLellan and A.P. Dobson. 1986. Habitat fragmentation in the
temperate zone. Pages 237-256 in M.E. Soule, ed., Conservation £iolo{>v-The
Science of Scarcity and Diversity. Sinauer Associates, Sunderland, MA.
56
-------
Wilcox, B.A. 1980. Insular ecology and conservation. Pages 95-11'
B.A. Wilcox, eds., Conservation Biology-an Evolutionary-!
7 iii M.E. Soule and
Ideological Perspective.
Sinauer Associates, Sunderland, MA,
Wilson, E.O., ed. 1986. Biodiversity. National Academy Press, Wzishington, DC.
3-18 in E.O. Wilson,
Wilson, E.O. 1988. The current state of biological diversity. Pages
ed., Biodiversity. National Academy Press, Washington DC
Worrest, R.C, andi.D. Grant. 1989. Effects of ultraviolet-B radiation
plants and marine organisms. Pages 197-206 in R.R. Jones
Depletion-Health and Environmental Consequences.
West Sussex, England.
Zaret, T.M. and R.T. Paine. 1973. Species introduction in a tropical lake. Science 182-
449-455.
57
on terrestrial
and T. WJgley, eds.,
.. John Wiley & Sons,
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