Zoos play an important role in conserving biodiversity by holding threatened species in captivity. Roughly one in seven threatened terrestrial vertebrate species are represented in zoos worldwide according to the International Species Information System database. While zoos are concentrated in temperate regions, most threatened species are found in tropical areas, highlighting a mismatch. Zoos collectively hold sizable populations of certain threatened species and their long-term data on reproduction and survival could help parameterize models to aid conservation efforts. However, zoos must strive to ensure populations are self-sustaining in the long-run and increase participation from regions with high biodiversity.

1. POLICYFORUM UNTIL 2:00 PM US ET THURSDAY, 17 MARCH 2011
EMBARGOED
CONSERVATION
An Emerging Role of Zoos Roughly one in seven threatened terrestrial
vertebrate species are held in captivity,
to Conserve Biodiversity
a resource for ex situ conservation efforts.
D. A. Conde,1* N. Flesness,2 F. Colchero,1 O. R. Jones,1 A. Scheuerlein1
A
t the October 2010 meeting of the global amphibian population declines (11). resented and 4% of amphibians. Our primary
Convention on Biological Diversity Captive breeding for reintroduction has focus is on species of conservation concern;
(CBD) in Nagoya, Japan, delegates downsides. Sociopolitical factors can deter- for mammals, roughly one-fifth to one-quar-
discussed a plan to reduce pressures on the mine the success of programs. For example, ter of threatened (19) and Near-Threatened
planet’s biodiversity. Key targets include reintroduction of Arabian oryx (Oryx leu- species are represented in ISIS zoos (see
expanding coverage of protected areas, halv- coryx) in central Oman was hampered by the figure) (table S1). With the exception of
ing the rate of loss of natural habitats, and poaching, partly because local communities Critically Endangered species, which only
preventing extinction of threatened species were insufficiently involved in conservation have a 9% representation (tables S1 and S2),
(1). For species whose habitat is severely efforts (12, 13). Furthermore, captive breed- the picture is similar for birds. For amphib-
threatened, however, the outlook is so bleak ing is costly, and technical difficulties can ians, the representation of threatened spe-
that the International Union for Conservation arise such as hybridization [breeding among cies is much lower (~3%); this is a concern
of Nature (IUCN), the U.S. Endangered Spe- different species (14), e.g., if current cryp- because amphibians are a highly threatened
cies Act, and the CBD (Article 9) recognize tic species are managed as one species, but group, with 41% of described species listed
that in situ conservation actions (i.e., in the are later split into several species according as threatened or Extinct in the Wild (EW) (5).
species’ natural habitat) will need to be com- to new taxonomic information]. The abil- The IUCN threat-level assessment for rep-
bined with ex situ approaches, such as captive ity of individuals to learn crucial skills that tiles has not been completed, so our results
breeding in zoos, aquariums, and so on (2, 3). allow them to survive in the wild (e.g., fear should be interpreted with caution, but of the
Captive breeding may be the only short- of humans or predators) may be compro- 1672 species already evaluated, zoos hold
term practical conservation option for species mised. In many cases, these difficulties have 37% of threatened and 18% of Near-Threat-
confined to dwindling habitats (4). However, been overcome by creative and species-spe- ened species.
captive breeding is absent or plays a minor cific measures. For example, it was feared Overall, zoos and aquariums hold roughly
role in the policies of most governments, con- that Puerto Rican parrots (Amazona vittata) one in seven threatened species (15%), but it
servation organizations, and multilateral insti- would be unable to escape predators in the is important to consider also the number of
tutions. To shed light on the state of captive wild, but this problem was solved with a pre- individuals held. Although individual zoos
breeding and its potential to contribute to con- release aviary-based stimulation and exercise might not have large populations of a par-
servation goals, we estimate the number of program (15). Because ex situ conservation ticular species, collectively, zoos hold siz-
threatened species already held in captivity. programs can be challenged when called into able populations of certain species, including
action at the last possible moment with only a highly threatened ones (see the figure). Zoos,
Captive Breeding few remaining individuals of a species, cap- as a global network, should strive to ensure
Although ecosystem health should be a con- tive breeding should not simply be seen as that their populations of threatened species
servation priority, a recent evaluation of the “emergency-room treatment.” It is a tool that can survive in the long term. However, each
status of the world’s vertebrates (5) noted that should be considered before the species has zoo may make a larger conservation contri-
captive breeding played a major role in the reached the point of no return. bution by specializing in breeding a few at-
recovery of 17 of the 68 species whose threat risk targeted species, rather than aiming to
level was reduced [e.g., Przewalski’s wild Counting Threatened Species in Captivity increase its species diversity, as specialization
horse (Equus ferus przewalskii) (6), black- We used the International Species Informa- increases breeding success (4).
footed ferret (Mustela nigripes) (7), and Cal- tion System (ISIS) database to estimate the Ultimately, success of conservation
ifornia condor (Gymnogyps californianus) number of threatened species already held in actions depends on the extent to which birth
(8)]. Captive breeding has the potential to captivity. ISIS is an organization that holds and death rates permit populations to survive
maintain targeted populations as an “insur- the most comprehensive information on in the wild (8). Population viability analyses
ance policy” against threats like disease or animals held in zoos and aquariums world- (PVAs) are used to forecast the probability of
pressure from nonnative species [e.g., egg wide, with records of ~2.6 million individu- population extinction for conservation pro-
predators on islands (9)] until reintroduction als shared among ~800 member institutions grams (20), but these require parameteriza-
into the wild is possible. A striking example (16). From the IUCN Red List of Threatened tion with data on age-specific birth and death
is the increase of amphibian collections in Species (17), we obtained the threat category rates (21). Adequate data from natural envi-
zoos (10) as a response to chytridiomycosis, of each terrestrial vertebrate species repre- ronments are often unavailable, especially for
a fungal infection responsible for precipitous sented in ISIS (18). [See supporting online threatened species (20). The zoo network has
materials (SOM) for details.] large long-term data sets, including data such
1
Max Planck Institute for Demographic Research, Rostock One-quarter of the world’s described bird as average litter size, interval between succes-
18057, Germany. 2International Species Information Sys- species and almost 20% of the mammal spe- sive litters, and age at maturity, which could
tem, Eagan, MN 55121, USA. cies are held in ISIS zoos (table S1). Only be used to fill these gaps. Of course, zoo data
*Author for correspondence: conde@demogr.mpg.de 12% of the described reptile species are rep- should be used with caution because they
1390 18 MARCH 2011 VOL 331 SCIENCE www.sciencemag.org

2. POLICYFORUM
EMBARGOED UNTIL 2:00 PM US ET THURSDAY, 17 MARCH 2011
Mammals Birds Reptiles Amphibians
800
Described
In zoos
600
Number of species
400
200 18%
24% 23% 17%
25% 37%
17%
19% 9% 28% 51% 6% 4% 3%
100% 100% 18% 0% 2% 50%
0
NT VU EN CR EW NT VU EN CR EW NT VU EN CR EW NT VU EN CR EW
5000
250 250 250 250
Number of individuals
500
50 50 50 50
50 10 10 10 10
5
1
Percentage of
species per interval 21 27 25 27 8 40 29 23 6 40 32 22 24 10 18 48
Species (ranked by number of individuals)
NT: Near threatened VU: Vulnerable EN: Endangered CR: Critically endangered EW: Extinct in the wild
Threatened
Endangered species in zoos. (Top) The number of able for design of conservation programs, 7. J. Belant, P. Gober, D. Biggins, in IUCN Red List of Threat-
species with IUCN status, globally described (color policy-makers must encourage and facilitate ened Species, Version 2010.4 (IUCN, Gland, Switzerland,
2010).
bars) and in ISIS zoos (black bars). (Bottom) The the participation of zoos from regions with 8. V. J. Meretsky, N. F. R. Snyder, S. R. Beissinger, D. A. Clen-
number of individuals in ISIS zoos for species listed high levels of biodiversity threat in global denen, J. W. Wiley, Conserv. Biol. 14, 957 (2000).
by IUCN—for mammals (142 species), birds (83 spe- networks, such as ISIS and the World Asso- 9. J.-C. Thibault, J.-Y. Meyer, Oryx 35, 73 (2001).
cies), reptiles (90 species), and amphibians (29 spe- 10. Amphibian Ark, www.amphibianark.org.
ciation of Zoos and Aquariums (WAZA). 11. L. F. Skerratt et al., EcoHealth 4, 125 (2007).
cies). The vertical broken lines show the boundaries
by 250, 50, and 10 individuals. The large numbers of
The potential for zoos to contribute to 12. J. A. Spalton, M. W. Lawerence, S. A. Brend, Oryx 33, 168
individuals classified as Vulnerable and Near Threat- conservation is not a new concept for the zoo (1999).
13. V. Morell, Science 320, 742 (2008).
ened are omitted for clarity. See SOM for details. community. Zoos and aquariums have devel- 14. R. Barnett, N. Yamaguchi, I. Barnes, A. Cooper, Conserv.
oped conservation projects in the wild, along- Genet. 7, 507 (2006).
side research and education programs (23). 15. T. H. White, J. A. Collazo, F. J. Vilella, Condor 107, 424
(2005).
do not necessarily reflect the situation in the For example, members of WAZA collectively 16. International Species Information System, www.isis.org.
wild, such as population flexibility in the face spend ~U.S. $350 million per year on conser- 17. IUCN, IUCN Red List of Threatened Species, Version 3.1
of changing conditions. vation actions in the wild, which makes them (IUCN, Gland, Switzerland, 2009); www.iucnredlist.org.
18. ISIS and IUCN information were matched on the species
Despite their current and potential contri- the third major contributor to conservation level using the Catalogue of Life (F. A. Bisby et al., Eds.);
butions to species conservation, ISIS zoos are worldwide after the Nature Conservancy and www.catalogueoflife.org.
concentrated in temperate regions, whereas the World Wildlife Fund global network (24). 19. Threatened species are those listed as Critically Endan-
gered (CR), Endangered (EN), or Vulnerable (VU) by IUCN.
most threatened species are tropical (5, 22) Given the scale of the biodiversity challenge, 20. T. Coulson, G. M. Mace, E. Hudson, H. Possingham,
(fig. S1). This mismatch between the areas it is vital that conservation bodies and policy- Trends Ecol. Evol. 16, 219 (2001).
where captive populations are held and their makers consider the potential that zoos as a 21. J. M. Reed et al., Conserv. Biol. 16, 7 (2002).
22. R. Grenyer et al., Nature 444, 93 (2006).
native range poses a challenge for imple- global network can provide. 23. WAZA, Building a Future for Wildlife: The World Zoo and
mentation of effective conservation actions. Aquarium Conservation Strategy (WAZA, Berne, Switzer-
Acclimatization to a new home is likely to be References and Notes land, 2005).
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