The current biodiversity extinction event: Scenarios
for mitigation and recovery
Michael J. Novacek*
and Elsa E. Cleland
*American Museum of Natural History, New York, NY 10024; and
Department of Biological Sciences, Stanford University, Stanford, CA 94305
The current massive degradation of habitat and extinction of
species is taking place on a catastrophically short timescale, and
their effects will fundamentally reset the future evolution of the
planet’s biota. The fossil record suggests that recovery of global
ecosystems has required millions or even tens of millions of years.
Thus, intervention by humans, the very agents of the current
environmental crisis, is required for any possibility of short-term
recovery or maintenance of the biota. Many current recovery
efforts have deﬁciencies, including insufﬁcient information on the
diversity and distribution of species, ecological processes, and
magnitude and interaction of threats to biodiversity (pollution,
overharvesting, climate change, disruption of biogeochemical cy-
cles, introduced or invasive species, habitat loss and fragmentation
through land use, disruption of community structure in habitats,
and others). A much greater and more urgently applied investment
to address these deﬁciencies is obviously warranted. Conservation
and restoration in human-dominated ecosystems must strengthen
connections between human activities, such as agricultural or
harvesting practices, and relevant research generated in the bio-
logical, earth, and atmospheric sciences. Certain threats to biodi-
versity require intensive international cooperation and input from
the scientiﬁc community to mitigate their harmful effects, includ-
ing climate change and alteration of global biogeochemical cycles.
In a world already transformed by human activity, the connection
between humans and the ecosystems they depend on must frame
any strategy for the recovery of the biota.
here is consensus in the scientific community that the current
massive degradation of habitat and extinction of many of the
Earth’s biota is unprecedented and is taking place on a cata-
strophically short timescale. Based on extinction rates estimated
to be thousands of times the background rate, figures approach-
ing 30% extermination of all species by the mid 21st century are
not unrealistic (1–4), an event comparable to some of the
catastrophic mass extinction events of the past (5, 6). The current
rate of rainforest destruction poses a profound threat to species
diversity (7). Likewise, the degradation of the marine ecosystems
(8, 9) is directly evident through the denudation of species that
were once dominant and integral to such ecosystems. Indeed,
this colloquium is framed by a view that if the current global
extinction event is of the magnitude that seems to be well
indicated by the data at hand, then its effects will fundamentally
reset the future evolution of the planet’s biota.
The devastating impact of the current biodiversity crisis moves
us to consider the possibilities for the recovery of the biota.
Here, there are several options. First, a rebound could occur
from a natural reversal in trends. Such a pattern would, however,
require an unacceptably long timescale; recoveries from mass
extinction in the fossil record are measured in millions or tens of
millions of years (10). Second, recovery could result from
unacceptably Malthusian compensation—namely, marked re-
duction in the world population of human consumers. Third,
some degree of recovery could result from a policy that protects
key habitats even with minimal protection of ecosystems already
altered or encroached on by human activity (i.e., protecting
‘‘hotspots’’). A fourth recovery scenario involves enlightened
human intervention beyond simple measures of wilderness pres-
ervation, a strategy that embraces ecosystem management and
mitigation of the current alteration of global biogeochemical
cycles. Here, strong preference is expressed for the last of these
options. Clearly, the future of evolution of the planet’s biota
depends significantly on what we do now to minimize loss of
species, populations, and habitats. At the same time, there is
acute recognition of the challenges and potential shortcomings
of many attempts at remediation and recovery. It is hoped that
this panel’s consideration of major threats, their interaction, and
the linkage between science and conservation in mitigating these
threats suggest some feasible recovery scenarios at several
Lessons from the Past: Recovery as a Long-Term Phenomenon
It is clear that the fossil record powerfully indicates the reality
of extinction on many scales, the magnitude as well as selectivity
of effects, and the pattern of recovery and survival (11, 12). To
what extent then does the fossil record help us in forecasting both
scenarios for extinction and recovery in the current crisis?
Consideration of this question moves us to acknowledge that
there are several aspects of these past events that diminish their
relevance to the current situation.
First, ancient mass extinction events have been documented
over comparatively long or imprecise timescales. The current
crisis has been extended through historical times, a matter of
centuries or a millennium, with a greatly accelerated impact that
began during the 20th century with the exponential increase of
world human populations. Thus, a period of only 75 to 100 years
may be most critical to the transformation of the present biota.
Second, mass extinction events of the past are typified by
global scale ecological transformation. By contrast, the current
event is typified by a ‘‘patchy’’ pattern involving habitat frag-
mentation and loss, where impacts vary markedly for different
habitats and different regions of the world (13). There is a large
body of evidence that suggests global climate changes and
alteration of global biogeochemical cycles may cause widespread
transformations of ecosystems, but significant biodiversity loss
has not yet been linked to these impacts.
Third, data on mass extinction events in the fossil record often
fail to provide a clear connection between a primary cause and
effect (14–16). In contrast, the current biodiversity crisis has one
obvious biotic cause: ourselves. Moreover, the source of the
trauma also has the presumed capacity to mitigate its own
deleterious impact. Although the extinction of many species may
be an irreversible outcome of the current event, certain aspects
of human-caused global change are reversible.
This paper was presented at the National Academy of Sciences colloquium, ‘‘The Future of
Evolution,’’ held March 16 –20, 2000, at the Arnold and Mabel Beckman Center in Irvine, CA.
To whom reprint requests should be addressed. E-mail: email@example.com.
May 8, 2001
no. 10 www.pnas.org兾cgi兾doi兾10.1073兾pnas.091093698
All of the above distinctions are pertinent to any scenario for
recovery that might be extracted from fossil and geological
evidence. Various reviews suggest that replenishment and di-
versification of the biota following mass extinction events re-
quired a recovery phase of millions or tens of millions of years
(10, 12, 15). Surely such estimates based on fossil data indicate
the time lag that might be expected for a natural recovery of the
biota following the current extinction event. Nonetheless, such
lessons from the past do not effectively inform our scenarios for
either current extinction or recovery given the emphatic role of
humans in both processes.
Near-Term Scenarios for Recovery: A Strategy
Given the limited applicability of the record of past extinction
events for examining the current environmental crisis, it seems
appropriate to turn to near-term recovery scenarios—namely,
scenarios that relate to human intervention just as they flow
from human causation. Such a consideration involves at least
three steps. First, we must identify the threats to the biota and
the entities most vulnerable to these threats. Second, we must
consider the scientific principles or strategies that inform pre-
scriptions to alleviate the threats. Third, we must apply feasible
recovery strategies to aspects of the biota that are not filtered out
during the transformation.
Any consideration of recovery also comes with an important
provision. Recovery cannot be decoupled from preventative
measures—namely, the environmental expression of ‘‘preventa-
tive medicine.’’ In other words, any success in recovery is
profoundly dependent on the state of what we have to work with.
Many recovery measures have failed because of the utterly
degraded and poorly understood state of the habitat at the time
of remediation. At the very least, a proper consideration of the
degree and nature of the threat and the scientific validity of
a chosen remediation—namely, steps one and two—must be
Our working group identified some primary current threats to
biodiversity, which include: (i) pollution, (ii) over-harvesting,
(iii) environmental shifts (climate change, disruption of biogeo-
chemical cycles, etc.), (iv) introduced, invasive species (biotic
exchange), (v) habitat loss and fragmentation through land use,
and (vi) disruption of community structure in habitats.
This list bears some expected convergence on a set of drivers
of change in terrestrial (excluding freshwater) ecosystems pro-
jected by Sala et al. (13) to have the greatest impact by the year
2100. These authors provide some predictions of change that
depend on the degree of interaction of the drivers. The extent to
which such global scale analyses frame a strategy for conserva-
tion priorities is likely to be a matter of debate for some time.
What follows here is a consideration of the threats and the
strategies for their mitigation that seem most grounded in
credible scientific approaches.
Pollution. The environmental movement, inspired by Rachel
Carson’s (17) powerful disclosure of the deleterious impact of
DDT and other pesticides, focused on the effects of toxins and
other pollutants long before the more complex and subtle
impacts of land use, biotic exchange, and climate change had
been carefully considered. Nonetheless, recovery from environ-
mental changes induced by pollution still faces severe problems
in both analysis and action. During the last four decades, use of
pesticides has tripled to 2.5 million metric tons of herbicides,
fungicides, and insecticides each year, a massive load on the
world’s ecosystems represented by 50,000 different products
(18). The deleterious effects of water-borne contaminants on
both fresh water and marine ecosystems are well documented
(19–22). Scientific analyses are critical to the ongoing effort to
understand this chain of events and to improve guidelines for
One danger addressed by such efforts is the mismatch between
the scale of the effect and the cause. The devastation of the coral
reefs, sea grasses, and kelps in the Caribbean has been promoted
by the loss of benthic producers whose viable populations in turn
may have been greatly reduced by pollutants in runoff released
through human activity along the shoreline (8, 9). What may at
first appear to be a complex crisis of subtle ecological dynamics
could have a very direct and efficiently corrected cause—namely,
the introduction of the pollutants in the first place. One con-
structive effort here is the continual refinement of categories of
pollutants according to both the scale (global and local) and
intensity (degree of toxicity, mutagenic impact, etc.) of the
effects. This often requires exacting experimental work, as in the
identification of a link between polyvinyl chlorides (PVCs) in
packaging and carcinogenic chemicals (21). Such toxin detective
work must be applied to a much broader range of potential cases.
Overharvesting. There is of course a clear and overlapping
relationship between overharvesting and other threats to biodi-
versity, such as land use, but the matter deserves distinction here.
Overharvesting impacts natural habitats with food sources that
are less dominated by agriculture or other human activities that
lead to transformation of the habitat.
Perhaps the most notable targets for overharvesting are
freshwater and marine ecosystems. Intensive and indiscriminant
fishing in freshwater systems, such as Lake Victoria in East
Africa has demonstrable catastrophic impacts on biodiversity
(23, 24). Likewise, Marine fisheries respond to food demand with
catches often comprising large species, lopping off each summit
of the food pyramid as populations of larger, top-level consum-
ers are virtually eradicated (9). Humans harvest the equivalent
of 24–35% of all diatom production in coastal and continental-
shelve areas of the oceans via fish harvests (22, 25). Practices that
minimize the effects of harvesting are often insufficiently
grounded and weakly executed (26). Massive catches of species
such as shrimp involve significant bycatches that are simply
There are success stories in constraining overfishing that
should provide models for other practices. Strict management is
resulting in recovery of summer flounder, mackerel in some
areas, and most notably, striped bass (26). The apparent resur-
gence of lobster populations off the Maine coast clearly dem-
onstrates the necessity of excluding large, gravid females as well
as young from the catch and developing a surveillance for both
the lobster fishing sites and the few points where catches are
brought ashore for transport. A more analytical approach to
constraining overharvesting also requires a revision in the
standards and criteria for the haul. Most prescriptions for
maximum sustainable yield (msy) concern only one species to the
detriment of other species in the relevant food web. This
selectivity disrupts ecologically sound practices that minimize
the bycatch and preserve the balance of populations of inter-
acting species. There is a clear need for better multispecies
models and harvesting strategies.
Environmental Shifts: Climate Change and the Alteration of Global
Biogeochemical Cycles. We continue to recognize the interplay
between the transformation of the physical environment at three
levels: hydrosphere, atmosphere, and lithosphere. As indicated
by the current trends, the feedback among these three levels will
intensify and the rate of change will accelerate. In recent years,
two aspects of such shifts have received the most attention—
climate change, involving both elevated carbon dioxide concen-
trations in the atmosphere and global warming, and nitrogen
Some suggest that the effects of climate change on the current
biota are already observable in the terms of physiology, distri-
bution, and phenology (27). For example, warming of the oceans
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May 8, 2001
could seriously impact on the convergence of warm water and
cold water that is responsible for the nutrient-rich upwelling in
the Southern Ocean off the coast of Antarctica. This change in
current regimes could in turn reduce one of the sea’s main
staples: krill. These organisms account for about 250 million
tons of food for whales, fish, seals, and other species annually,
more than two and half times the annual yield of the world’s
The likelihood of unwelcome effects of climatic change pre-
sents a severe test for international science and environmental
policy. The Kyoto Protocol, which sets specific targets for
greenhouse gases for heavily industrialized nations—such as the
reduction of CO
emissions by 5% of 1990 levels by 2008–
2012—is an exemplary melding of scientifically based recom-
mendations and policy; but it remains to be seen whether it will
be widely ratified. Indeed, representatives of the Organization of
Petroleum Exporting Countries (OPEC) are demanding finan-
cial compensation in the event that the goals of the Kyoto
Protocol are realized and the demand for fuel oil decreases. As
broad scale climatic change so emphatically transgresses regions,
environments, and national boundaries, the success of recovery
from detrimental effects of climatic change depends perhaps to
a greater extent than any other measure on international coor-
dination and cooperation.
A second major source of disruptions to the global environ-
ment is nitrogen deposition, ranked by Sala et al. (13) to be the
third most influential driver of biodiversity change during the
coming century. Human activity has essentially doubled the
amount of nitrogen cycled globally (28), contributing to nitrogen
sinks in soils, surface waters and deep oceans, and the atmo-
sphere, and this increase has detrimental effects on biodiversity
and ecosystem function.
Recovery efforts aimed at correcting the destructive aspects of
nitrogen deposition often hinge on a simple recognition of the
problem. Conservation actions to secure wildlife reserves rarely
take into account the fact that nitrogen can negatively affect such
reserves. Because nitrogen is transported globally through air
and water, it can easily impact on areas and reserves that are
seemingly in balance. Mitigation strategies must include anti-
pollution efforts and control of fertilizer application. Because
fertilizer is the greatest human source of additional nitrogen
(28), there is a nascent effort to monitor and constrain its use.
Studies of reduced nitrogen fertilizer use in Mexico (29) showed
that crop yield and economics were sustained or even improved,
while loss of nitrogen from the environment occurred at accept-
ably lower levels. More case studies of this kind are needed.
Introduced or Invasive Species. Biotic exchange is rampant and
humans as agents are effective in all regions of the globe (30).
Some of the more dramatic examples, such as the introduction
of the Nile Perch into Lake Victoria and the resultant decimation
of at least 200 endemic cichlids (23), offer sobering experiments
that demonstrate the catastrophic effects of invasive species.
Other introductions, such as plant species to the United King-
dom (31), do not seem to promote extinction of native plants
because the invaders are restricted to habitats, such as roadsides
and construction sites, that are highly disturbed by humans.
Regardless of their magnitude, human-mediated introductions
of species in new habitats and areas has and will continue to be
one of the major drivers of biotic change (13, 32).
As biotic communities are widely infiltrated, it is critical to
identify the degree of deleterious alteration by specific criteria.
For example, it is difficult to generalize whether original habitats
that are species-rich or species-poor are more or less susceptible
to invasion. The probability and impact of biotic exchange is also
closely tracked to other drivers, such as land use policy and
introduction of excess nitrogen deposition through use of fer-
tilizers. Accordingly, good policy to minimize biotic exchange
must account for drivers that may promote an insidious and
unintentional introduction of harmful species.
A key consideration in limiting biotic introductions, or at least
their deleterious effects, relates to the nature of the maintenance
of the ecosystem that is threatened by the introductions. Exper-
iments conducted on patchy distributions, gene flow, and vagility
of key community species (33) indicate a priority for preserving
processes that maintain the balance within the community, not
just the state described just before the onset of the invasion.
Again, these strategies dovetail with land use and preservation
policy. Fragmentation of habitats impedes the security of these
processes because it restricts the movement and gene flow
exchange of the resident, noninvasive organisms. On the other
hand, the restoration of the historic disturbance regime, such as
the reintroduction of fire in a community dependent on fire for
seed germination or the removal of dams that prevent seasonal
flooding necessary for establishment, has a way of reducing the
invasive efforts and favoring the endemic components.
Habitat Loss and Fragmentation Through Land Use. Land use has
been ranked as the most intensive driver of terrestrial environ-
mental change in the coming century (13). Forecasted needs for
world human populations over the next few decades will, if
anything, accelerate massive demands on natural habitats. In 30
years there will be a need to feed an estimated 8.2 billion people,
32% more than exist today. To boost food production by the
required 50 or 60%, grain harvest will have to increase by 2% a
year, whereas agricultural breakthroughs have produced only
1.8% cumulative total growth for the 10 years between 1985 and
1995 (34). The harvesting required will have its own negative
consequences; land use over the past two decades presents a
disturbing picture of degradation. Over the past 20 years some
5 billion tons of topsoil have been removed and during the past
40 years at least 4.3 million square kilometers of cropland (more
than twice the size of Alaska) have been abandoned because of
soil loss. Each year, an estimated 13 million ha of tropical forests
are destroyed, causing the loss of 14,000–40,000 species (35).
Projections for the impact of land use on the planet’s biota are
indeed so stark that any conservation effort seems engulfed by
the tide of human activity. Yet there are scientifically grounded
strategies and even some success stories in the effort to constrain
the rampant destruction of natural habitats. One of these
strategies applies criteria emphasizing marked biodiversity, high
proportion of uniquely restricted (endemic) species, and vulner-
ability of ecosystems to a ranking of ‘‘biodiversity hotspots.’’
Building on earlier proposals (1, 7), Myers et al. (36) identified
25 of the most obvious hotspots on continents and oceanic
islands as high priority sites for intensive study and conservation
effort. These designated crisis zones contain 44% of all species
of vascular plants and 35% of all species in four vertebrate
groups (mammals, birds, reptiles, and amphibians), yet they
represent only 1.4% of the earth’s surface.
Whether such a priority-based program for hotspot conser-
vation is applied by governments or by international protocol, it
is important to recognize one feature shared by many of these
and other natural habitats: they are already in a marked state of
degradation. Eleven of the 25 hotspots cited (36) have already
lost 90% of their primary vegetation and three of these have lost
95%. Moreover, the average proportion of area currently pro-
tected for the total designated area of these hotspots is only
37.7%. Even areas that do receive a higher degree of ‘‘official
protection’’ are highly vulnerable to threats from outside the
system, including the climate change, pollution, nitrogen depo-
sition, and species invasions noted above.
These observations underscore the need for realism and
practicality, combined with solid scientific evidence, in any
measures to minimize the impact of land use on biodiversity. We
are obviously past any point where strategies that focus on
www.pnas.org兾cgi兾doi兾10.1073兾pnas.091093698 Novacek and Cleland
preservation of ‘‘pristine’’ habitats are sufficient for the job.
Greater attention must be placed on human-dominated land-
scapes that represent contours encircling the less disrupted
areas. This is critical to identifying corridors or ‘‘landscape
linkages’’ that facilitate the continuity among the less damaged
habitats and help secure biological processes critical to func-
tioning ecosystems (37). The approach is well exemplified in
protocols established by Cowling et al. (38) for maintenance of
viable ecological and evolutionary processes in the Cape Flo-
ristic Region, a remarkable area containing 12,000 plant species,
80% of which are endemic.
The size of either a ‘‘core area’’ or a ‘‘linkage area’’ is of course
critical to securing biological process. It may be safely assumed
that the bigger the area the more likely the processes will be
maintainable and will require less recovery effort and interven-
tion. Reality dictates, however, that the land secured for man-
agement will likely be smaller than the area desired. Therefore,
high intensity scientific research on species identity, diversity,
composition, distribution, trophic relationships, vagility, gene
flow, and other patterns and processes must inform any decisions
about the characteristics, including size, of the areas designated
for conservation. Disclosures on species and their distributions
for diverse organisms, including poorly known groups such as
soil invertebrates, insects, bacteria, and fungi, can identify new
critical areas of high endemism. Insights into ecological rela-
tionships build on such fundamental biodiversity information by
providing some minimum expectations for core area or linkage
area size. They specify a lower bound under which ecosystem
processes will break down. Such work is critical to defining
ecotones or ecological gradients that closely relate to the sta-
bility of the ecosystem in a given region. Such insights are
necessary for developing practical and effective conservation
strategies, especially where human populations and wildlife
communities are so highly integrated.
Disruption of Community Structure in Habitats. The threat to the
basic workings of community dynamics is, as noted above,
broadly overlapping with other threats including land use. Yet
this factor is distinguished here because ecological disruption is
not only a manifestation of the reduction in size of the original
habitat. Ecological havoc can occur in areas where, at least on
the face of it, the original habitat has been ‘‘protected.’’ Such
putatively secured habitats may be vulnerable to many threats,
such as population fragmentation of keystone species, disruption
of biogeochemical cycles, or invasive species. One of the most
disruptive factors to community stability is the interference with
a balance of evolutionary processes, such as genetic drift and
gene flow, that ensure genetic variation in species (33).
The importance of ecological relationships as a cornerstone to
conservation of natural landscapes can be appreciated in the case
of large-bodied species. Although information on the diversity
and interactions in a great range of biological groups may be
lacking for a given area, the need to secure relatively large areas
for larger-bodied species is straightforward. As Western notes
(37), maintaining this simple equation between area size and the
protection of large-bodied species is important because the loss
of the latter allow unwanted and significant changes to the
ecological processes inherent in the community. Hence, the
focus of conservation effort on some of the large, more charis-
matic species in major wildlife reserves is not only a matter of
aesthetics or biophilia; it is critical to maintaining basic ecolog-
ical relationships within the community.
Consideration of the roles of large-bodied species or other
ecological functions in a community has pivotal importance in
maintaining natural habitats, especially where a more complete
picture of both the diversity and interactions within the com-
munity is still lacking. Such studies provide threshold values for
securing core and linkage areas in both relatively isolated and
human-dominated habitats. It is apparent that such parameters
lead to conservation plans that can preserve not only the major
components of diversity within an ecosystem, but the interac-
tions that ensure the viability of the community as a whole. There
are notable success stories based on this premise. Analysis of the
breeding and migratory patterns of Chinook salmon (which can
grow to 100 pounds as adults) in the State of Washington’s Elwha
River led to the recommendation to remove the two dams that
inhibited the movement of the salmon upriver. The study showed
that such an action would restore Chinook salmon populations
to their former size—annually, about 400,000 adults. These
recommendations inspired government action that would rep-
resent the most significant effort to reverse more than a century
of dam building and help restore the nations rivers and their
Biodiversity Loss and Recovery Scenarios in Human-Dominated
Repeated throughout this discussion is the notion that the
success of any restoration or recovery practice hinges on the state
of what ‘‘we’ve caught in the net.’’ Thus, vastly improved
information on the basic state of the world biota and the various
comparative states of degradation ongoing or projected remains
a profoundly important goal for the conservation of biodiversity.
The level of the challenge this goal presents can be appreciated
when we consider the imbalance between urgency and invest-
ment. Patterns of species diversity and endemism critical to
identifying hotspots or other conservation priorities are the
products of work by experts in systematic biology—the science
involving the identification, analysis of evolutionary relation-
ships, and classification of diverse species and the groups that
contain them. Only about 6,000 specialists (40) are responsible
for organizing and updating the database on the 1.6 million
named species, and potentially millions of more species yet to be
discovered. Indeed, the cataloged species already represented by
nearly 3 billion specimens in museums, botanical gardens,
herbaria, frozen tissue collections, seed banks, bacteria type
cultural collections, zoos, and aquaria are inadequately covered
by the world’s systematists (40, 41). The problem is especially
acute when one considers that many of the countries that own
hot spots and otherwise account for 80% of the world’s named
species have only about 6% of the world’s scientists in any field.
Building taxonomic and management capacity in these countries
is essential to the success of conservation efforts. Such scientific
investments that serve international conservation interests are
meager compared with investments in space exploration (36).
It is well recognized, nonetheless, that the accumulation of
scientific information itself is not the solution to our ecological
problems. As we strive to improve our knowledge of biodiversity
and ecological relationships we must also deal with perhaps the
most subtle and complex community relationship within those
ecosystems—the multifaceted roles of our own species. As
Janzen (42) remarked, ‘‘The wildland garden is not humanity
free and it never can be.’’ The recognition that the planet is
embraced by human-dominated ecosystems (37, 43) undercuts
any assumption that we can restore the biota back to some state
recognized as ideally pristine and ‘‘uncontaminated’’ by the
mark of human populations. Human activity is as much, or more,
a part of the ecological equation as any other factor. The
problem of how human populations can adopt practices that are
mutually beneficial to themselves as well as to the sustainable
state of the biota remains. Some impractical hubris here should
be avoided. There is little justification to convincing farmers that
intensified monoculture is less productive and sustainable than
the application of biodiversity extraction, because the latter is so
limited relative to intensive farming (37, 44). Even successful
conservation actions, such as the restoration effort of the Elwha
River noted above (39), were spurred on by a shift in human
Novacek and Cleland PNAS
May 8, 2001
needs and priorities—in this case an interest in larger salmon
populations for food, sport, and ecotourism.
At a more general level, the most effective argument that
human activities should safeguard biodiversity is the need to
secure the basic ecosystem services dependent on that diversity.
Ecosystem process and function effected by a critical number of
interacting species secures the quality of the environment on the
broadest front and, thus, has direct impact on human health and
well-being (45). This is not an easy argument to make to highly
competitive and heavily consuming populations in industrialized
countries or to impoverished, marginalized populations in de-
veloping countries. But the argument, nonetheless, must be
made, through demonstration of the services the natural world
provides and the benefits of living compatibly with biodiversity.
In the world of uncertainty surrounding the nature of global
biodiversity, the nature of its destruction, and the most effective
steps for mitigating that destruction, scenarios for recovery are
far from clear. Nonetheless, our review and discussion of many
aspects treated in this colloquium do permit several general
impressions and recommendations. Although major extinction
events of the past underscore the reality and the possibility of
such catastrophes today and in the future, they provide limited
insight on the current biodiversity crisis. Such past extinction
events do, however, suggest that if recovery is left to natural
processes, the rebound of global ecosystems to some state
beneficial to many of its species, including humans, is measured
in unacceptably long timescales—on the order of millions or
even tens of millions of years. Intervention on the part of the
source of these current traumas, namely humans, is required for
any possibility of recovery or even maintenance of the biota in
any condition that approaches its present state.
Current efforts on this front suffer from several deficiencies,
including a lack of basic information concerning the diversity
and distribution of species, ecological processes, and relative
magnitude of threats (land use change, pollution, nitrogen
deposition, and others) in many habitats and regions. A much
greater and more urgently applied investment to address these
deficiencies is obviously warranted.
In addition, many plans for conservation and restoration in
human-dominated ecosystems have not achieved sufficient con-
nections between agricultural or harvesting practices and bio-
logical sciences. A number of threats to biodiversity require
particularly intensive international cooperation and input from
the scientific community to mitigate their harmful effects,
including climate change and alteration of global biogeochemical
cycles. The overarching recognition that we live in a world
already radically transformed by human activity must frame our
strategies for effecting maintenance or recovery of our vital
In addition to colloquium organizers Norman Myers and Andrew Knoll,
we thank F. Bazzaz, D. Bramble, D. Erwin, J. Jackson, S. Kark, A.
Templeton, D. Western, and others for their participation in the panel
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