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Transcript
Focus: Brave New World
REWILDING
NORTH
AMERICA
One
elephant
at
a
time
By Alexandra Mushegian
G
round sloths occupy a small but
beloved role in the collective
imagination. These five-ton, seventeenfoot hamster-like herbivores, which
went extinct somewhere around 10,000
years ago, are commonly found as
skeletons posing in natural history museums. Populations of these animals
were thriving in North America when
humans first arrived over the Bering
Land Bridge along with mammoths,
lions, saber-toothed cats, twenty-pound
beavers, and several species of giant
tortoise, not to mention a multitude of
deer and ox-like species. Shortly after
humans arrived, they all died out.
The Pleistocene epoch, which ended
10,000 years ago (in archaeological
terms, the end of the Paleolithic), was
a golden age of animal exoticism worldwide. Why it ended—why this geological period saw a series of massive global
collapses of large animal biodiversity—
is a contentious topic. Many argue that
the primary reason was climate change
in the form of global deglaciation.
Increasingly, though, studies are suggesting that it was human activity, in the
form of hunting, habitat alteration, and
the introduction of new diseases, that
was the major cause of these extinctions.
Without exception, the timing of major
biodiversity reductions on all continents
and large islands coincides with the arrival of early humans, with many species
dying out within a few hundred years
after humans arrived (1).
The only continents still possessing
noteworthy megafaunal diversity—
Africa, and to a lesser extent, Asia—are
the continents where humans coevolved
with animals for the longest time. Now,
due to political and socioeconomic instability in those
regions, they are in danger
there too.
Some scientists believe
that the loss of large vertebrate biodiversity has
graver consequences than
merely a reduction in worldwide
biodiversity. Ecological studies suggest
that large herbivores and predators are
crucial to maintaining healthy, robust
ecosystems. Some see the loss of these
species as one that will have perilous future consequences. In response, they’ve
come up with a controversial plan: they
want to bring them back to the USA.
14 Harvard Science Review • fall 2008
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Focus: Brave New World
group dedicated to rescuing fish habitats such as mangroves and salt marshes.
But the radicalism of the Pleistocene
rewilding concept lies in the scale of
the project in both time and space.
Proponents of this plan want to restore
ecosystems that existed 13,000 years
ago, and they want to revert to wilderness areas of thousands of square miles.
Stipulating carefully planned, progressive ecological studies and small-scaled
experiments, Pleistocene rewilding
would see the introduction of giant
tortoises, horses, camelids (llamas), and
most unexpectedly, lions, cheetahs, and
elephants to the American Southwest
and Great Plains regions. All of these
species had close relatives living in
North America during the Pleistocene
(the Asian elephant, for example, is
more closely related to the woolly mammoth than it is to the African elephant)
(4). These species would be set loose
to pursue their normal predator-prey
interactions to reshape the American
environment.
This plan would represent a shift in
conservation practice from focusing
on cataloging and slowing biodiversity
loss to actively managing and promoting
“Stipulating carefully
planned, progressive
ecological studies
and small-scaled
experiments,
Pleistocene rewilding
would see the
introduction of giant
tortoises, horses,
camelids (llamas), and
most unexpectedly,
lions, cheetahs, and
elephants to the
American Southwest and
Great Plains regions.”
Mammoths are one of the
groups of animals that lived on
the North American landmass
before becoming extinct.
credit: Gianni Dagli Orti/Corbis Science Vol 319. 7 March 2008 p. 1331
Pleistocene Rewilding
In 2005, a group of scientists published a two-page proposal in Nature.
This short paper had enormous scope
and ambition. In response to what they
saw as the takeover of North America
by “dandelions and rats,” Josh Donlan
and his colleagues proposed that a viable solution might be to use African
and Asian species as analogues of
extinct Pleistocene North American
species, introducing them to areas of
North America set aside to become the
wilderness again. If done right, they
claimed, this method would restore
North American ecological health and
save species from extinction (2).
Ecological restoration projects are
undertaken all the time. Peregrine falcons, for example, were on the brink
of extinction from DDT contamination before a program bred together
several subspecies from both the New
and Old Worlds and reintroduced them
into the wild. Peregrines have proven to
be adaptable and appear to be thriving
(3). Many conservation agencies strive
to restore endangered habitats, such as
the National Oceanic and Atmospheric
Administration’s Restoration Center, a
fall 2008 • Harvard Science Review 15
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Focus: Brave New World
The diagram to the left maps
the correlation between human
arrival and extinction of indigenous species, as well as the
strength of that evidence.
productive, diverse ecosystems.
credit:Science Volume 306 . 1 October 2004
The Plan
Pleistocene rewilding would start
with small-scale ecological studies of
the way exotic species respond to being
repatriated to North American environments. These studies would start
with less dramatic species—tortoises,
llamas—and would progress to more
challenging species like big cats. Many
species, such as cheetahs, already exist
in captivity in the US; they would be
placed on large private properties with
potential prey and the predator-prey
interactions and dynamics over time
would be carefully studied by experts
on the species (5). In addition, information about the flora of the Pleistocene
could be reconstructed from pollen in
the fossil record.
Once there is a significant body of
research, the next step would be to find
huge tracts of land to be rewilded. The
authors of the paper suggest economically depressed regions of the Great
Plains as good candidates for such an
endeavor. The area would be securely
fenced and given the status of a national
park or nature preserve. Hopefully, it
would become a tourist attraction that
would bring economic benefits to the
surrounding region.
Similar plans are already being attempted in at least two spots in the
world: Oostvaardersplassen, a nature
reserve in the Netherlands focusing on
restoration of large ungulates, and Lenskiye Stolby, Siberia, commonly known
as “Pleistocene Park.” (6).
The Benefits of Rewilding
Why exactly are large vertebrates so
important? Various studies show that
predators, as well as some of
the more impressive herbivores, play a disproportionately large role in maintaining “ecological function.”
“Ecological function” means,
roughly, an ecosystem’s ability to rebound from shocks,
adapt to changing conditions, and evolve to greater
and greater fitness—in other
words, general vitality. Predators help control herbivore
populations, keeping them
from over-expanding, destroying all vegetation, and
subsequently starving. The
importance of this “topdown” control effect has
been confirmed in many situations. Plant biomass declined
by 40% in parts of the Arctic
tundra from which predators
were excluded (7). Closer to home,
many areas of the United States are
facing problems because out-of-control
deer populations are decimating forests
and living perpetually half-starved and
disease-ridden (and also carrying Lyme
disease, a debilitating illness that is
spread from deer to humans by ticks)
(8). Deers’ previous predators, wolves
and mountain lions, are largely absent
in the wild because they were hunted
as dangers by humans, and because
their forest habitats are too fragmented
to allow them to have the large areas
they need to thrive. A recent review of
multiple studies from Venezuelan terrestrial and various marine ecosystems
concludes that “we live in a largely topdown regulated world” (9).
Large herbivores, too, contribute to
ecosystem diversity, usually by virtue
16 Harvard Science Review • fall 2008
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Focus: Brave New World
of their very size and gawkiness—for
example, elephants trample vegetation
and tortoises dig long burrows. These
sorts of activities create heterogeneity
in the environment, opening up a variety of ecological niches than can then
be filled by different plant and animal
species. The more diverse and varied a
landscape is, the greater its robustness
and adaptability. By feeding on shrubs
and saplings, elephants maintain grassland ecosystems; camelids feed on the
type of weedy, scrubby species that otherwise threaten to take over landscapes.
In the Siberian “Pleistocene Park,”
current studies are exploring the effects
of tundra wildlife on global warming.
Potentially, the activity of large mammals may disturb snow cover enough
to keep the soil continually exposed to
the cold, preventing permafrost from
melting and reducing the release of
additional CO2 from the soil (10).
North America today, with the disappearance of bison and the domination
of industrial-scale agricultural monocultures, is “impoverished,” according
to Harry Greene, a professor at Cornell and one of the co-authors of the
original proposal (5). Ecologically, he
says, “we can likely do better” (5). The
possibility of partially restoring the lost
ecological and evolutionary potential of
North American landscapes, he said in
an email interview, was in his opinion
the single best argument for Pleistocene
rewilding (5).
The Objections to Rewilding
A natural initial objection to the
Pleistocene rewilding proposal is pure
incredulity—elephants? Here? Once
one has heard the justification for the
proposal, concerns still remain about
viability and potential consequences.
One objection is that too much time
has passed since the Pleistocene for
the concept of ecologically analogous
species to be valid. Both the species
and the environment have undoubtedly
changed significantly since those times
and thus the introduction of exotic
species to a different continent could
have ecologically harmful effects due
to unforeseen interactions with the current natives. Furthermore, introduced
species could carry latent pathogens
that might thrive in a new setting, bringing diseases that might threaten both
nature and agriculture. Even if there are
not dramatically deleterious effects, the
desired outcome of increasing ecological function might simply not happe, if
assumptions about species interactions
and ecological roles turned out to be
wrong (12). Extensive research is certainly necessary to evaluate the threat
of these sorts of problems.
Obviously, there are economic considerations as well. The research leading
up to and during Pleistocene rewilding
efforts must be funded, as well as the
allocation of land, the installation of
fences around Pleistocene wilderness
areas, and the hiring of managers to
monitor the borders. The occasional escape would be inevitable and elephants
or lions on the loose would create a
terribly dangerous situation. .
“Cost might be a big deal, possibly
insurmountable,” Greene said. “But in
terms of if money were not an issue, I
think what really bugs people, including
fellow biologists, is not ‘exotics’ and so
forth, but rather [the idea of] bringing
back something that can kill us” (5).
The existence of Pleistocene wilderness
reserves would force people to adjust
their attitudes about the other animals
that share their landscape and return
a concern that North Americans have
largely not had to face for a long time.
Indirect economic consequences and
ethical problems will arise when the
question of where to get the animals
from is decided—currently, trade in
exotic species is largely prohibited and
negotiating with countries to acquire
their animals is likely to be complicated.
Along similar lines, there are fears that
North American Pleistocene rewilding will divert attention and resources
from conservation within Africa and
Asia (11).
Questions to Ponder
The debate about Pleistocene rewilding raises deep and important questions
about humans’ role in the biosphere.
Are we responsible for atoning for
the destructiveness of our thirteen
thousand year old ancestors? Are we a
species like any other, our capacity for
destruction just part of our evolutionary advantage? Or is it now our role to
serve as large-scale gardeners, making
sure the world thrives? What does it
mean when we influence the course of
evolution? As the idea of Pleistocene
rewilding gains attention, we will have
to take a look at just how well we know
the species with which we share the
planet.
—Alexandra A. Mushegian ’10 is an Organismic and Evolutionary Biology concentrator in Currier House.
References
1. Burney DA and Flannery TF, “Fifty millenia of
catastrophic exinction after human contact” (2005).
Trends in Ecology and Evolution 20:7.
2. Donlan CJ et al, “Re-wilding North America”
(2005). Nature 436:18.
3. Tordoff HB and Redig PT, “Role of genetic background in the success of reintroduced peregrine
falcons” (2001). Conservation Biology 15:2.
4. Donlan CJ et al, “Pleistocene Rewilding: An optimistic agenda for twenty-first century conservation”
(2006). The American Naturalist 168:5.
5. Greene, Harry. Personal correspondence, October
2008.
6. Curry, Andrew, “Pleistocene Park: Where the auroxen roam” (2008). Wired magazine, 22September
2008, accessed online October 2008 at http://www.
wired.com/science/planetearth/magazine/16-10/
mf_bison?currentPage=1.
7. Aunapuu, M. “Spatial patterns and dynamic
responses of arctic food webs corroborate the exploitation ecosystems hypothesis (EEH)” (2008). The
American Naturalist 171:2.
8. Fairfax County, VA. “Deer Management Activities Fairfax County, Virginia.” http://www.fairfaxcounty.
gov/comm/deer/deermgt.htm#info. Accessed October 2008.
9. Banse K. “Do we live in a largely top-down
regulated world?” (2007). Journal of Biosciences
32:791-796.
10. Donlan et al 2006 Zimov SA, “Pleistocene Park:
Return of the mammoth’s ecosystem” (2005). Science 308:5723.
11. Rubenstein DR at al, “Pleistocene park: does rewilding North America represent sound conservation
for the 21st century?” (2006). Biological Conservation
132:232-238.
12. Ibid.
fall 2008 • Harvard Science Review 17
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