The Ecoscience column focuses on habitat and biodiversity conservation to save species from extinction.
Paul Ehrlich (Bing Professor of Population Studies and
Professor of Biological Sciences, Stanford University) and
Anne Ehrlich (Senior Research Associate, Department of
Biological Sciences, Stanford) are familiar names to
ecologists and environmentalists everywhere. But while most
folks are aware of the Ehrlichs' popular writing in the
areas of ecology and overpopulation (most of us — for
instance — have read Paul's book The Population
Bomb ) . . . few people have any idea of how deeply the
Ehrlichs are involved in ecological research (the type that
tends to be published only in technical journals and
college texts). That's why we're pleased to present this
regular semi-technical column by these well-known
As we've pointed out in our last few columns, most of this
planet's animals, plants, and micro-organisms can be
effectively saved from extinction only if they're allowed
to reproduce in their natural settings. Therefore, the
ability to conserve populations and species boils down
— for all intents and purposes — to the ability
to conserve habitat.
Now the broad outlines concerning just how this
should be accomplished are simple in principle.
First of all, no more virgin land should be
developed anywhere. There are already plenty of disturbed
areas available to fill the needs of people . . . if human
population growth is brought under control in as rapid and
humane a manner as possible.
It's true, of course, that there is currently a shortage of
decent housing in the United States, but that problem could
be remedied by the high-density redevelopment of such
places as the South Bronx, Spanish Harlem, and East Los
Angeles. In a similar vein, the additional food required by
poor countries could likely be obtained through the use of
an ecologically sound intensification of agriculture,
rather than by bringing more marginal land under
cultivation (and most of the acreage that is now
uncultivated is agriculturally marginal).
As a first step, the few remaining undisturbed lands of
Earth should be transformed into reserves, with human
access to them strictly controlled. Furthermore, such areas
would have to be protected not only from activities like
building, mining, logging, and off-road vehicle travel but
also from the more subtle threats of air pollution, acid
rain, and pesticide drift. (The atmosphere, you see,
doesn't respect human-made territorial boundaries.)
NOT GOOD ENOUGH
Unfortunately, the creation of such a reserve system
wouldn't, by itself, be enough to guarantee the
preservation of Earth's biological riches . . . because
much of the diversity originally contained in reserves will
be lost, once such areas become "islands". In order to
understand why that would happen, we'll have to
make a short excursion into an area called "island
biogeography". Some 15 years ago, two leading ecologists
— the late Robert H. MacArthur and Edward O. Wilson
(of "sociobiology" fame) — postulated that the number
of species on an island normally remains more or less
constant, and is determined primarily by two factors:
successful colonization by new species and extinction of
The two scientists concluded that — everything else
being equal — the larger the number of species, the
higher would be the rate of extinction . . . since the
island would then be more crowded and the population size
of each species, on the average, would be smaller. On the
other hand, the fewer the residents, the easier it would be
for "colonist" species to find space to settle in.
Additionally, the rate of extinction would be influenced by
such factors as island size . . . that is, the smaller the
island, the higher the extinction rate would probably be.
The arrival rate of potential colonists also would vary
with the size of the island, since random wanderers would
be more likely to "hit" a large target than a small one.
And, of course, distance from the nearest mainland would
also be important in determining the flow of immigrants.
This "equilibrium theory" makes sense . . . and it's
supported by some actual data. For instance, the 1883
explosion of the volcano Krakatoa created a wasteland that
was slowly recolonized. The number of bird species there
gradually increased from zero to 27 . . . where it has
stayed, even though five of the first 27 species went
extinct (that is, the island's population died
out) and were replaced by five other varieties.
Any area of the planet's surface can be thought of as being
similar to an island . . . with the composition of its
flora and fauna determined by rates of colonization and
extinction of species. With that in mind, then, picture
what happens when a nature reserve is established and
becomes isolated from other similar areas by extensive
intervening terrain made up of, say, farmland.
Immediately, the extinction rate in the reserve will start
to rise, as the area will almost certainly be too small to
support as many populations as were once supported by the
larger habitat area that formerly surrounded it.
Individuals of species that were at first present —
because they were part of a larger population that occupied
an area bigger than the preserve — will start to disappear.
At the same time, the inflow of potential colonist
varieties will dwindle, because the surrounding farmland
presents a barrier to the movement of individuals. Since
the extinction rate will be up, and the colonization rate
down, the number of species at equilibrium will be reduced.
This means that the flora and fauna will become less
Ten thousand years ago — when the great glaciers of
the last ice age melted and the sea levels rose —
just such a relaxation, or reduction in diversity, occurred
among the mammal fauna found in certain Asian areas that
became islands. In fact, none of these "new" islands
— even the very large ones — were able to
retain the entire spectrum of fauna found on the Asian
mainland. Judging by what happened there, then, it's quite
possible to predict what would happen if all present
African game parks should become completely isolated
"islands". About half of the large mammal species
would be lost from the average reserve in some 500 years,
and there would be less predictable — but doubtless
substantial — losses among other groups of animals
and plants, as well.
It's plain, then, that the maintenance of only one or a few
small reserves in each land region would be a hopelessly
inadequate measure to protect the present diversity of life
for any length of time. Even under the most careful
protection, small, deeply isolated reserves would gradually
suffer enormous losses of species. And large ones, even if
they included connecting corridors to other reserves, could
be expected to have significant losses.
THOUGHTFUL CONSERVATION DEVELOPMENT
Since our goal should be to preserve as much as possible of
the planet's biological diversity more or less permanently,
it would obviously be unwise to place all our eggs in the
admittedly fragile reserve basket. Developed and disturbed
areas must also be made more hospitable to organisms other
than humankind . . . in order to permit more and larger
populations to be maintained and to provide corridors for
migrants to travel when passing between the fully protected
There are many ways that this could be accomplished.
Diversity could be introduced to tree farms, for instance.
Contrary to present practice, several species should be
planted together, and shrubs and herbs might be encouraged
to grow beneath the trees. In addition, the use of
hedgerows or windbreaks between farm fields should become
standard practice, as should the setting aside of woodlots
in agricultural areas.
Under such a redevelopment program, city parks, vacant
lots, and the "roughs" of golf courses would be planted
with native species, while exotic weeds would be suppressed
wherever possible. Lawns would be replaced with natural
landscaping. The herbiciding of roadsides and powerline
right-of-ways would have to stop, too, as would the lining
of streams with concrete.
Wherever possible, efforts would be made to restore
disturbed areas to nearly natural habitats. The ecosystem
that once occupied an overgrazed mountain range, strip
mine, parking lot, or building site can never be precisely
replaced, but — with effort — useful ecosystems
could be established in such places . . . ecosystems that
would contain a wide variety of native organisms.
Most important, though, any program to conserve
biological diversity must include a reduction in the
burning of fossil fuels (which is the root cause of acid
rain) and the institution of the strictest emission
controls when such fuels are used. Limitations in
the use of pesticides and synthetic fertilizers must also
be incorporated in the plan . . . as well as provisions for
spreading the practice of soil conservation and for
bringing an end to overgrazing.
CONSERVATION'S "IRON LAWS"
All of these measures may be thought of as the necessary
tactics of conservation. However, their
implementation will require a strategy as well . .
. one that, we believe, should be based on five "Iron Laws
 In conservation, there is only successful defense or
retreat . . . never a true advance. A species or an
ecosystem, once destroyed, cannot be restored.
 Conservation and continued growth of human population
are fundamentally incompatible.
 Conservation and a growthmanic economic system are also
 The notion that only the short-term goals and immediate
happiness of Homo sapiens should be considered in
making moral decisions about the use of Earth is lethal . .
. not only to nonhuman organisms but to humanity as well.
 Arguments that support the right of nonhuman life-forms
to exist or that focus on their aesthetic value and
intrinsic interest — as well as appeals to compassion
for what may be our only living companions in the universe
— now mostly fall on deaf ears. Until our species'
ethical and aesthetic attitudes evolve further,
conservation must be promoted as an issue of human
well-being and, in the long run, human survival.
Thus, preserving the diversity of life will entail a
changed relationship not only between human beings and
their environment, but also among people. Our population
growth must be halted as soon as possible and a gradual
decline begun. The economic system must be reorganized . .
. so that it's oriented toward sustaining society
rather than toward maintaining perpetual growth. The gap
between rich and poor must be narrowed . . . not simply
because it's the moral thing to do, but because it's
essential that it be done if we're to avoid nuclear war and
preserve diversity. (Remember, the poor countries "own"
that most precious resource, our planet's species-rich
Most of all, time must be gained to complete the revolution
in ethics that will assure the right of all other organisms
to exist . . . and to insure that such a right is not
casually violated. For the last century, humanity has been
moving in the right direction . . . as demonstrated, for
example, by the increasing public concern for whales and
the institution of laws to protect animals against cruelty.
But we have a long way to go before such basic rights are
extended to all living things.
We believe that such an ethical revolution holds the
only real promise of conserving Earth's living
diversity in the long run. All people must become aware of
the needs and rights of other beings . . . and aware that
humanity is both morally and physically dependent on those
The tactics and strategy outlined here may seem extremely
impractical in a society caught up in the silliness of
"supply-side economics". Yet such a program is crucial to
the persistence of all of this planet's economic
systems, dependent as they are on the continuance of
ecosystem services. We hope that what seems impractical
today will be recognized as imperative a decade from now.
Any less comprehensive change — or any great delay
— is likely to mean that the job won't get done. And
then our own species will pay the price along with the
More information on the preservation of diversity can be
found in Extinction: The Causes and Consequences of the
Disappearance of Species by Paul and Anne Ehrlich
(Random House, 1981, $15.95). Their work in ecoscience is
supported in part by a grant from the Koret Foundation of
San Francisco, California. From January 23 to February 6,
1983 Anne and Paul Ehrlich, and their friends and
colleagues John and Cheryl Holdren, will join MOTHER for an
educational South Pacific Seminar on the islands of Tahiti,
Bora Bora, Rangiroa, and Huahine. For information on this
and other tours, turn to page 74 of this issue.