Pleistocene Park: Does re-wilding North America represent sound conservation for the 21st century?

Abstract

A group of conservation biologists recently proposed to populate western North America with African and Asian megafauna, including lions, elephants, cheetahs, and camels, to create a facsimile of a species assemblage that disappeared from the continent some 13,000 years ago. The goals of this program, known as “Pleistocene re-wilding”, are to restore some of the evolutionary and ecological potential that was lost from North America during the Pleistocene extinctions, and help prevent the extinction of selected African and Asian mammals. Pleistocene re-wilders justify this conservation strategy on ethical and aesthetic grounds, arguing that humans have a moral responsibility to make amends for overexploitation by our ancestors. They believe that the flora of many North American terrestrial ecosystems has gone basically unchanged since the end of the Pleistocene, so re-wilding would help restore evolutionary and ecological potential and improve ecosystem functioning. This paper discusses some of the pros and cons of this proposal, including the ethical, aesthetic, ecological, and evolutionary issues, assesses its potential economic and political impacts on other conservation practices, both in North America and elsewhere, and reviews the realities of large mammal reintroductions. It is concluded that Pleistocene re-wilding with exotic species will not restore the evolutionary or ecological potential of native North American species nor extinct Pleistocene megafauna and their ancient ecosystems, but may instead jeopardize indigenous species and North American ecosystems. Resources would be better spent on preserving threatened organisms in their native habitats and reintroducing them to places in their historical ranges from which they were only recently extirpated.

Full text

Pleistocene Park: Does re-wilding North America
represent sound conservation for the 21st century?
Dustin R. Rubenstein
a,
*, Daniel I. Rubenstein
b
, Paul W. Sherman
a
, Thomas A. Gavin
c
a
Cornell University, Department of Neurobiology and Behavior, Seeley G. Mudd Hall, Ithaca, NY 14853, USA
b
Princeton University, Department of Ecology and Evolutionary Biology, Guyot Hall, Princeton, NJ 08544, USA
c
Cornell University, Department of Natural Resources, Fernow Hall, Ithaca, NY 14853, USA
ARTICLE INFO
Article history:
Received 28 November 2005
Received in revised form
27 March 2006
Accepted 2 April 2006
Available online 5 June 2006
Keywords:
Pleistocene re-wilding
Equid
Reintroduction
Extinct
Megafauna
Evolutionary and ecological
potential
ABSTRACT
A group of conservation biologists recently proposed to populate western North America
with African and Asian megafauna, including lions, elephants, cheetahs, and camels, to
create a facsimile of a species assemblage that disappeared from the continent some
13,000 years ago. The goals of this program, known as ‘‘Pleistocene re-wilding’’, are to
restore some of the evolutionary and ecological potential that was lost from North America
during the Pleistocene extinctions, and help prevent the extinction of selected African and
Asian mammals. Pleistocene re-wilders justify this conservation strategy on ethical and
aesthetic grounds, arguing that humans have a moral responsibility to make amends for
overexploitation by our ancestors. They believe that the flora of many North American ter-
restrial ecosystems has gone basically unchanged since the end of the Pleistocene, so
re-wilding would help restore evolutionary and ecological potential and improve ecosys-
tem functioning. This paper discusses some of the pros and cons of this proposal, including
the ethical, aesthetic, ecological, and evolutionary issues, assesses its potential economic
and political impacts on other conservation practices, both in North America and else-
where, and reviews the realities of large mammal reintroductions. It is concluded that
Pleistocene re-wilding with exotic species will not restore the evolutionary or ecological
potential of native North American species nor extinct Pleistocene megafauna and their
ancient ecosystems, but may instead jeopardize indigenous species and North American
ecosystems. Resources would be better spent on preserving threatened organisms in their
native habitats and reintroducing them to places in their historical ranges from which they
were only recently extirpated.
Ó2006 Elsevier Ltd. All rights reserved.
1. Introduction
Ancestors of elephants and lions once roamed much of North
America (Martin, 1984). Recently, a diverse group of conserva-
tion biologists has proposed to create a facsimile of this by-
gone era by reintroducing charismatic African and Asian
megafauna to western North America to replace species that
disappeared during the Pleistocene extinctions, some 13,000
years ago (Donlan et al., 2005). Arguing that their vision is jus-
tified on ‘‘ecological, evolutionary, economic, aesthetic and
ethical grounds’’, Donlan et al. (2005) believe that modern
‘‘Pleistocene Parks’’ would provide refuges for species that
are themselves threatened or endangered, and that repopu-
lating the American west with these large mammals would
0006-3207/$ - see front matter Ó2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.biocon.2006.04.003
*Corresponding author: Tel.: +1 607 254 4325; fax: +1 607 254 4308.
E-mail address: drr24@cornell.edu (D.R. Rubenstein).
BIOLOGICAL CONSERVATION 132 (2006) 232–238
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journal homepage: www.elsevier.com/locate/biocon

improve local landscapes, restore ecological and evolutionary
potential, and make amends for the ecological excesses of our
ancestors.
To understand the uniqueness of this proposal, a termi-
nological clarification is necessary. The ‘‘re-wilding’’ of eco-
systems is the practice of reintroducing extant species
(captive-bred or wild caught) back to places from which they
were extirpated in historical times (i.e., in the past several
hundred years). Because re-wilding deals with recently
extirpated species and short evolutionary time scales, it is
reasonable to assume that there have been minimal evolu-
tionary changes in the target species and their native habi-
tats. Re-wilding of ecosystems is not a new conservation
practice and, indeed, it has become a standard management
tool (Foreman, 2004).
By contrast, ‘‘Pleistocene re-wilding’’ of ecosystems is a
revolutionary idea that would involve introducing to pres-
ent-day habitats either (1) extant species that are descended
from species that occurred in those habitats during the Pleis-
tocene, but that went extinct about 13,000 years ago, or (2)
modern-day ecological proxies for extinct Pleistocene species.
Pleistocene re-wilding is thus a novel plan for ecological res-
toration on a more grandiose temporal and spatial scale than
is re-wilding (Callicott, 2002).
Pleistocene re-wilding has been discussed for many years
(Soule
´, 1990; Martin and Burney, 1999), and in 1989, it was at-
tempted in Siberia, Russia, when mega-herbivores including
wood bison (Bison bison athabascae), Yakutian horses (Equus
sp.), and muskoxen (Ovibos moschatus) were introduced in an
effort to recreate the grassland ecosystem of the Pleistocene
(Zimov, 2005). However, the North American Pleistocene re-
wilding proposal of Donlan et al. (2005) is far more ambitious
than this because it aims to reconstruct an ancient ecosystem
by translocating a more diverse array of African and Asian
megafauna to geographical regions and plant communities
that have evolved without such creatures since the Pleisto-
cene. Species targeted for introduction span several trophic
levels and include predators such as African cheetahs
(Acinonyx jubatus) and lions (Panthera leo), and large herbivores
like African (Loxodonta africana) and Asian (Elephas maximus)
elephants, various equids (Equus spp.), and Bactrian camels
(Camelus bactranus)(Donlan et al., 2005). This plan includes
animals that are both descendant species of extinct taxa
and ecological proxies for extinct species.
Pleistocene re-wilding of North America has two principle
goals: (1) to restore some of the evolutionary and ecological
potential that was lost from North America 13,000 years
ago; and (2) to help prevent the extinction of some of the
world’s existing megafauna by creating new, and presumably
better protected, populations in North America (Donlan et al.,
2005). Discussion of the proposal is just beginning (Soule
´,
1990; Martin and Burney, 1999; Callicott, 2002; Foreman,
2004; Donlan et al., 2005) and, although some initial concerns
have been raised (Chapron, 2005; Dinerstein and Irvin, 2005;
Schlaepfer, 2005; Shay, 2005; Smith, 2005), supporters and
detractors agree that Pleistocene re-wilding is a bold and
innovative idea, deserving of careful consideration. This pa-
per was developed with the intent of extending healthy and
fruitful scientific debate about Pleistocene re-wilding of North
America.
2. The ecology and evolution of Pleistocene
re-wilding: restoring ecological potential to North
American ecosystems
Although an ethical desire to redress the excesses of our
ancestors might serve as an initial justification for Pleistocene
re-wilding, the ecological and evolutionary merits of such a
plan must be considered carefully. Pleistocene re-wilding of
North America would involve a monumental introduction of
large mammals into areas where they have been extinct for
millenia, and into habitats that have existed without such
creatures for similarly long periods of evolutionary time.
The potential negative ecological effects of transplanting exo-
tic species to non-native habitats are well-known (Mack et al.,
2000). The results of Pleistocene re-wilding in North America
are unknown and might well be catastrophic; ecosystem
functioning could be disrupted, native flora and fauna,
including species of conservation value (Smith, 2005), could
be negatively impacted, and a host of other unanticipated
ecological problems could arise.
Pleistocene re-wilders believe that it is possible to enhance
ecological potential, that is, to recreate evolutionarily-rele-
vant mammalian species assemblages and restore ecosystem
functioning to Pleistocene levels, because they believe that
the flora of North American ecosystems is essentially un-
changed since the Pleistocene (Soule
´, 1990; Donlan et al.,
2005). However, plant communities are dynamic and con-
stantly in flux, genotypically and phenotypically, and there
has been over 13,000 years for grassland and shrub-steppe
communities to evolve and plant assemblages to change in
the absence of the full suite of Pleistocene mega-herbivores
(Zazula et al., 2003). When managers discuss restoring ecolog-
ical potential, or simply ecosystem restoration, it is important
for them to be clear about what they are trying to restore and
to what level of restoration they are trying to reach (Jordan
et al., 1987). Whereas Pleistocene re-wilding could potentially
increase the ecological potential of some of North America’s
ecosystems by reintroducing predators on species like prong-
horn or bighorn sheep (and thus, indirectly restoring the evo-
lutionary potential of these prey species), or by restoring
herbivorous keystone species like elephants to the temperate
grasslands, it is questionable whether it would restore ecolog-
ical potential to Pleistocene levels.
Indeed, rather than restoring our ‘‘contemporary’’ wild
ecosystems to the ‘‘historic’’ wild ecosystems of the Pleisto-
cene and their original levels of ecosystem functioning, which
are unknown, Pleistocene re-wilding could instead result in
‘‘re-wilded’’ novel, or emerging, ecosystems with unique spe-
cies compositions and new or altered levels of ecosystem
functioning (Hobbs et al., 2006)(Fig. 1). Biogeographic assem-
blages and evolutionary lineages would be co-mingled in no-
vel ways; new parasites and diseases could be introduced
(Viggers et al., 1993; Cunningham, 1996); and food chains
would be disrupted. Moreover, without really knowing how
Pleistocene ecosystems functioned, there will be no way to
determine whether Pleistocene re-wilding restored ancient
ecosystems or disrupted contemporary ones.
While the reintroduction of large grazers can, in some
cases, shape and restore grassland ecosystems (Zimov et al.,
1995), this will depend on whether the grazers are indigenous
BIOLOGICAL CONSERVATION 132 (2006) 232–238 233

or exotic. Modern introductions of exotic feral horses have
dramatically altered vegetation in marsh (Levin et al., 2002)
and grassland (Zalba and Cozzani, 2004) ecosystems through-
out the New World, and these changes have had direct im-
pacts on a variety of native animal species, some positive,
but some negative. Moreover, exotic grazers, such as the
one-humped camel (Camelus dromedarius), have wreaked ha-
voc upon desert ecosystems in Australia by selectively eating
rare plant species (Edwards et al., 2001). Similarly, the reintro-
duction of large predators can also have unexpected results
on populations of prey species. For instance, wolves reintro-
duced to Yellowstone National Park, USA preyed upon elk
more, and other species of ungulates less, than what was pre-
dicted prior to reintroduction (White and Garrott, 2005).
Of course, it might be argued that these problems would
quickly become apparent if Pleistocene re-wilding were first
attempted on a small-scale, experimental basis. However,
experiments of this nature cannot be done quickly and may
take decades and generations to play out. For instance, the
Siberian Pleistocene Park experiment began in 1989, and as
of yet, few of the results have been published (Zimov, 2005).
Moreover, it may not be possible to conduct adequate, mean-
ingful experiments on small spatial scales because many of
these species have large home ranges or migrate great dis-
tances. For instance, African cheetahs can have home ranges
of nearly 200 km
2
(Broomhall et al., 2003), and African ele-
phants can migrate distances of up to nearly 150 km or more
(Thouless, 1995).
Despite the potential dangers to ecosystem functioning,
the reintroductions proposed by Donlan et al. (2005) would
place many of the animals in temperate grasslands and
shrub-steppe habitats, which are among the most threatened,
but least protected, ecosystems in the world (Hoekstra et al.,
2005). If the reintroduction of exotic megafauna could help
preserve these ecosystems, conservationists must weigh the
possibility of preserving disrupted or novel North American
ecosystems against the possibility of losing those ecosystems
altogether.
3. The ethics and aesthetics of Pleistocene
re-wilding: protecting and restoring the evolutionary
potential of threatened megafauna
Humans were at least partly responsible for exterminating
some species of Pleistocene megafauna (Martin, 1984;
Burney and Flannery, 2005) and, today, anthropogenic im-
pacts continue to contribute to the extinction of the world’s
remaining megafauna (IUCN, 2004). Donlan et al. (2005) ar-
gue that humans bear an ethical responsibility to prevent
future megafaunal extinctions and redress past losses. They
suggest that introducing large Asian and African vertebrates
to North America will not only ensure their long-term sur-
vival, but also restore their evolutionary potential (i.e., in-
crease the number of individuals worldwide to allow them
greater chances to radiate and generate new phenotypic
and genotypic variants). Although this plan is certainly
well-intentioned, the underlying reasoning is flawed. In es-
sence, it is an attempt to preserve charismatic African and
Asian species that are being driven to extinction by humans
in their native habitats by refocusing efforts in places
where those species have never occurred and where hu-
mans drove their distant ancestors extinct. Although Don-
lan et al. (2005) do not advocate giving up on conserving
megafauna in developing nations, diverting attention from
some of the world’s most economically poor, but most bio-
logically rich, countries to make amends for the ecological
excesses of our North American ancestors could cripple,
rather than assist, the conservation movement worldwide
(Chapron, 2005).
The human population is growing and natural habitats are
declining in extent and diversity everywhere. Couple this with
the political and economic strife that is occurring in many
developing nations and it is not difficult to see why native
megafauna, especially large mammals, are declining in num-
bers worldwide (Muwanika et al., 2005). Despite this dire situ-
ation, Pleistocene re-wilding of North America is not the only
viable solution to preserve the world’s megafauna. In the
developing world, new conservation models are being imple-
mented that go hand-in-hand with human development as
wildlife must pay for itself by generating economic benefits
for local citizenry to help alleviate poverty (Kiss, 2004; Naidoo
and Adamowicz, 2005). Although there are many challenges
in developing such programs, there is much to be gained by
overcoming them because most of the native megafauna in
developing regions inhabit private, often unprotected, lands
outside of parks. For instance, across Africa, 84% of African
elephant habitat is outside of protected areas (Blanc et al.,
2003), and in Kenya, 70% of the wildlife lives outside of pro-
tected areas for at least part of the year (Norton-Griffiths,
1998).
“Historic”
wild ecosystem
“Contemporary”
wild ecosystem
“Re-wilded”
novel ecosystem
Pleistocene
extinctions
Pleistocene
re-wilding
??
Fig. 1 – Re-wilders believe that Pleistocene re-wilding will lead to a restoration of the historic wild ecosystem and original
ecosystem functioning. However, re-wilding could result in a re-wilded novel ecosystem with unique species compositions
and new ecosystem functioning.
234 BIOLOGICAL CONSERVATION 132 (2006) 232–238

Conserving African and Asian megafauna does not require
relocating them to North America. However, it will require
new conservation plans that ensure local citizenry receive
economic benefits from wildlife. Available human and finan-
cial resources might be better expended on preserving land,
promoting ecotourism, building fences in areas of high hu-
man–wildlife conflict, and establishing educational and
research programs in areas of Africa and Asia where indige-
nous megafauna are most at risk, rather than on introducing
those same large, exotic species to North America.
In addition, the question of how the Pleistocene re-wilding
plan would affect existing conservation efforts in North Amer-
ica must be considered. Conservationists often struggle with
local opposition to re-wilding with native predators, and even
the reintroduction of relatively benign large mammals (e.g.,
moose) meets resistance (Lauber and Knuth, 1999). The
introduction of modern relatives of extinct predators will be
opposed even more strongly by state governments and lo-
cally-affected citizens (Shay, 2005). And, with good reason:
escapes are inevitable, resulting in human–wildlife conflict as
often occurs near protected areas in Africa and Asia. Ironically,
an article in the same journal issue as the one on Pleistocene re-
wilding of North America (Donlan et al., 2005) documents the
increasing numbers of humans killed by lions in Tanzania
(Packer et al., 2005). And only a few weeks later, news reports
surfaced from Ethiopia indicating that lions disturbed by defor-
estation killed 20 people and devoured 750 domestic animals
during August, 2005 (Anon, 2005). It is difficult enough for North
American conservationists to address the real concerns of local
citizens about attacks by mountain lions (native predators) on
joggers. One can only imagine the anti-conservation backlash
that would be generated by news coverage of farmers coping
with crop destruction by herds of elephants, or lions and chee-
tahs attacking cattle, or even children.
While Pleistocene re-wilding may help maintain the evolu-
tionary potential of modern, extant species, it cannot restore
the evolutionary potential of extinct species that no longer ex-
ist. And even attempting to restore evolutionary potential of
endangered species using modern-day species from foreign
continents as proxies for creatures that went extinct in North
America is controversial. Donlan et al. (2005) highlighted the
peregrine falcon (Falco peregrinus) to illustrate how using simi-
lar, but not genetically identical, (sub-)species can indeed serve
as proxies for nearly-extinct taxa. Moreover, for nearly two dec-
ades, conservation biologists have proposed introducing clo-
sely related proxy species for extinct birds on New Zealand
and other Pacific islands (Atkinson, 1988, 2001). However, spe-
cies that went extinct some 13,000 years ago are probably more
genetically different from their modern-day proxies, who have
continued to evolve for millennia, than are two sub-species of
modern falcons or modern Pacific island birds. For instance,
although recent molecular data suggest that the common
horse (Equus caballus) is genetically similar to its evolutionary
ancestral species (Weinstock et al., 2005), modern elephants
(Surovell et al., 2005), cheetahs (Barnett et al., 2005), and lions
(Barnett et al., unpublished manuscript) are quite genetically
distinct from their extinct Pleistocene relatives.
Rather than use modern-day species from foreign conti-
nents as proxies for creatures that went extinct in North
America, conservation efforts should focus on re-wilding na-
tive species into their historical ranges throughout North
America to restore ecosystems and increase the evolutionary
potential of indigenous species (Dinerstein and Irvin, 2005;
Schlaepfer, 2005). For instance, native herbivores like bison
(Bison bison), pronghorn (Antilcapra americana), elk (Cervus ela-
phus), jack rabbits (Lepus townsendii), and various ground-
dwelling squirrels (Spermophilus spp.) and prairie dogs
(Cynomys spp.), as well as native predators like black-footed
ferrets (Mustela nigripes), bobcats (Lynx rufus), badgers (Taxidea
taxus), and swift foxes (Vulpes velox) are likely candidates for
reintroduction to geographic regions from which they were
extirpated in the past several hundred years (Hoogland, 2006).
Donlan et al. (2005) suggested that another appropriate
candidate for reintroduction is the Bolson tortoise (Gopherus
flavomarginatus). Because this animal once lived throughout
the southwestern United States and still persists in small
areas of similar habitat in Mexico, it may not differ greatly
from its ancestral form and, therefore, it might be a reason-
able candidate for reintroduction. However, before attempting
such a reintroduction, one would also have to consider how
much the plant and animal communities in the tortoise’s na-
tive geographic habitats have changed (evolved) since this
reptile went locally extinct.
If reintroducing charismatic megafauna is an important
goal of Pleistocene re-wilding because of its possible galvaniz-
ing effect on public support for conservation, then one might
consider expanding reintroductions of some of North Amer-
ica’s own megafauna like wolves (Canis lupus) or grizzly bears
(Urus arctos) to other portions of their known recent (i.e., his-
torical) ranges. And if more predators are deemed necessary,
an even better candidate for re-wilding would be the puma
(Puma concolor), because it is more genetically similar to the
long-extinct American cheetah (Miracinonyx trumani) than
the African cheetah is to the American cheetah (Barnett
et al., 2005). Moreover, the puma is a native mammalian pred-
ator that barely survived the Pleistocene extinctions 13,000
years ago, and still remains threatened throughout much of
its North American range (Culver et al., 2000).
4. The economics and politics of Pleistocene
re-wilding: uncertainty and tradeoffs
The political and economic ramifications of Pleistocene re-
wilding of North America are unclear. Certainly, it will be
expensive because land acquisition and preparation, translo-
cation, monitoring, protection, and containment require con-
siderable human and financial resources (Fischer and
Lindenmayer, 2000). Moreover, all of these efforts would likely
cost proportionally more in North America than they would
in Africa or Asia, given the higher prices of salaries and sup-
plies. Because conservation funding is limited, Pleistocene re-
wilding may compete for resources that might otherwise
have gone to local conservation efforts (Chapron, 2005).
Although it is possible that introducing charismatic African
and Asian megafauna to North America could ignite public
and political support, ultimately leading to an overall increase
in funding for conservation projects worldwide, other new
ideas might increase the pool of resources with less risk to
North American ecosystems and conservation efforts
worldwide.
BIOLOGICAL CONSERVATION 132 (2006) 232–238 235

Donlan et al. (2005) are careful to point out that the initial
steps of Pleistocene re-wilding can occur without large-scale
translocations of proxy species because many of these ani-
mals are already in captivity in the United States. This would
potentially reduce costs, as well as avoid potential political
problems between the United States and developing nations,
the ultimate ‘‘sources’’ for the animals. However, reintroduc-
tions from wild populations have been more successful than
those from captive populations (Fischer and Lindenmayer,
2000; Griffith et al., 1989), and Pleistocene re-wilding inevita-
bly would involve translocating animals from Asia and Africa
to North America, either to increase population numbers or to
improve population viability by augmenting genetic diversity.
Such translocations of megafauna into areas where they were
recently extirpated occur routinely throughout Africa and
Asia (Fischer and Lindenmayer, 2000), and learning from
these examples could shed some light on the practicality of
Pleistocene re-wilding of North America.
5. The practicality of Pleistocene re-wilding:
the reality of reintroductions
One of the goals of Pleistocene re-wilding of North America is
to ‘‘...restore equid species to their evolutionary homeland’’
(Donlan et al., 2005) and, indeed, some of the best known
and most successful reintroductions of endangered species
to their historical ranges involve equids (Moehlman, 2002).
For example, the Tahki, or Przewalski’s horse (Equus ferus prze-
walskii), which is endemic to Mongolia and China, was con-
sidered extinct in the wild by the end of the 1960s and
fewer than 400 Tahki remained in captivity in 1979. By the
beginning of the 1990s, however, efforts began to reestablish
populations in the wild and two reintroduction sites were
chosen in Mongolia. By 2000, the population at one site had
declined only slightly, while that at the other had increased
by 50% (Wakefield et al., 2002). These encouraging trends led
to a third introduction in 2005 and suggest that the re-wilding
of the Tahki’s historic range is likely to succeed.
In an attempt to repopulate Israel with recently extirpated
biblical animals, onagers, a race of Asian asses (Equus hemi-
onus), were translocated from Israel’s Hai Bar breeding reserve
to a nearby erosional crater in the Negev desert. Between 1968
and 1993 multiple reintroductions of 50 individuals took
place. It was not until the end of the 1990s, however, before
the population started to expand numerically and spatially.
Low fertility of translocated adult females relative to that of
their wild-born daughters and male-biased sex ratios among
the progeny limited recruitment (Saltz and Rubenstein, 1995).
These unanticipated biological constraints suggest that even
reintroductions of native species to their historical habitats
are not assured of succeeding.
Repopulating the historic range of the endangered Grevy’s
zebra (Equus grevyi) in east Africa is viewed as critically impor-
tant to saving the species from extinction (Moehlman, 2002).
Fewer then 2000 Grevy’s zebras remain in small areas of Ethi-
opia and northern Kenya, whereas only 35 years ago, over
20,000 individuals inhabited areas all the way to the horn of
Africa. Efforts to repopulate areas of the Grevy’s historic range
have involved capturing and moving small groups of appro-
priate sex ratios and age structures to holding areas before
subsequent release. While two such reintroductions in Kenya,
one to Tsavo National Park and one to Meru National Park, be-
gan successfully, neither has led to expanding populations. In
fact, in Meru, differences in the composition and abundance
of mammal species in the Grevy’s zebras’ new range have,
at times, led to rapid declines in their numbers (D.I. Ruben-
stein pers. obs). Therefore, even reintroductions within the
natural geographic regions of a species are often fraught with
surprises due to diseases, unexpected differences in environ-
mental conditions, and naı
¨vete
´toward predators.
The Przewalski’s horse and the Asian ass are presented by
Donlan et al. (2005) as two candidate examples of endangered
equid species that could be saved from extinction, while also
being used to help restore equid species to their ‘‘evolutionary
homelands’’ in North America. Small-scale reintroductions of
these and other endangered equid species throughout Asia,
their historically-known evolutionary homeland, appear to
be working. These are appropriate reintroductions and the
sort of re-wilding that makes evolutionary and ecological
sense because the time between the species’ extirpation
and reintroduction has been short enough that neither the
native ecosystem nor the animals themselves have changed
(evolved) very much. However, as both the onager and the
Grevy’s zebra reintroduction programs illustrate, success is
not assured until more is known, underscoring the need to
treat reintroductions as continuing experiments in adaptive
management. Moreover, increasing the scope of reintroduc-
tions of extant endangered equids into places from which
they were extirpated recently, the only evolutionary home-
lands that we can be sure are suitable for them, is more jus-
tifiable evolutionarily and ecologically than introducing
them to North American habitats where they have not existed
for millenia.
6. Another Jurassic Park?
We all remember ‘‘Jurassic Park’’, Crichton’s (1990) fictional
account of re-wilding an isolated island with extinct dino-
saurs recreated from ancient DNA. Pleistocene re-wilding of
North America is only a slightly less sensational proposal. It
is a little like proposing that two wrongs somehow will make
a right: both the modern-day proxy species are ‘‘wrong’’ (i.e.,
different genetically from the species that occurred in North
America during the Pleistocene), and the ecosystems into
which they are to be reintroduced are ‘‘wrong’’ (i.e., different
in composition from the Pleistocene ecosystems, as well as
from those in which the modern-day proxy species evolved).
Pleistocene re-wilding of North America will not restore evo-
lutionary potential of North America’s extinct megafauna be-
cause the species in question are evolutionarily distinct, nor
will it restore ecological potential of North America’s modern
ecosystems because they have continued to evolve over the
past 13,000 years. In addition, there is a third and potentially
greater ‘‘wrong’’ proposed: adding these exotic species to cur-
rent ecological communities could potentially devastate pop-
ulations of indigenous, native animals and plants.
Although Donlan et al. (2005) argued that Pleistocene re-
wilding of North America is justified for ecological, evolution-
ary, economic, aesthetic, and ethical reasons, there are clearly
numerous ecological and evolutionary concerns. On the one
236 BIOLOGICAL CONSERVATION 132 (2006) 232–238

hand, the plan might help conserve and maintain the evolu-
tionary potential of some endangered African and Asian
megafauna, as well as indirectly enhance the evolutionary po-
tential of native North American prey species that have
lacked appropriate predators since the Pleistocene. On the
other hand, the plan cannot restore the evolutionary potential
of extinct species and it is unlikely to restore the ecological
potential of western North America’s grassland and shrub-
steppe communities. Instead, it may irreparably disrupt cur-
rent ecosystems and species assemblages. Moreover, there
are many potential practical limitations to Donlan et al.’s
(2005) plan. Reintroduced camels did not survive for long in
the deserts of the American West (Smith, 2005). Could African
megafauna, especially large carnivores, really populate the
same areas? Would the genetically depauperate cheetah
(O’Brien et al., 1985) succumb to novel diseases? Would ele-
phants survive the harsh prairie winters, lacking the thick
coats of their mastodon ancestors?
Answering these questions and accomplishing Pleistocene
re-wilding of North America would require a massive effort
and infusion of funds and could take more time to experi-
mentally test than some of these critically endangered spe-
cies have left to survive in their existing native habitats. If
financial and physical resources were available on this scale,
they would be better spent on developing and field-testing
new ways to manage and conserve indigenous populations
of African, Asian, and North American wildlife in their histor-
ically-populated native habitats, on conducting ecological,
behavioral, and demographic studies of these organisms in
the environments in which they evolved, and on educating
the public on each continent about the wonders of their
own dwindling flora and fauna.
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