11.5: Ex Situ Conservation Strategies
The best strategy for protecting biodiversity over the long term is to protect existing wild populations in their natural ecosystems. This strategy, known as on-site, or in situ conservation, not only protect entire ecological communities—including thousands of species and their interactions—but also natural processes and ecosystem services. However, if the last populations of a threatened species are too small to remain viable, if they continue to decline despite conservation efforts, or if their threats do not subside, then in situ conservation may prove ineffective. In such cases, sometimes the only option left to prevent an imminent extinction is to capture those last remaining individuals and transfer them to a facility where they can be cared for under artificial, human-controlled conditions. This strategy is known as off-site, or ex situ conservation, and may involve individuals that were collected in the wild, orphaned, confiscated, or displaced and have nowhere else to go. Thanks to ex situ efforts, several African plants and animals that are extinct in the wild continue to survive in zoos, aquaria, and botanical gardens. Examples include four to seven species of ancient cycads (Encephalartos spp.) from Southern Africa, and the pygmy Rwandan water lily (Nymphaea thermarum, EW), which is the world’s smallest water lily (IUCN, 2019).
For species facing imminent extinction, sometimes the only option left may be to capture the remaining individuals and transfer them to captivity.
Ex situ and in situ conservation are complementary strategies (Figure 11.13; see also Conde et al., 2011). For example, many ex situ conservation programs aim to raise enough healthy individuals to support translocation projects when appropriate habitats are available. Ex situ conservation efforts were instrumental in preventing the extinction of the live-bearing Kihansi spray toad (Nectophrynoides asperginis, EW). Populations of this Tanzanian endemic declined precipitously following the establishment of a hydroelectric dam, which caused the toad’s waterfall spray-zone habitat to dry up. The species was subsequently declared Extinct in the Wild in 2009. Tanzanian conservationists, however, demonstrated good foresight by inviting zoos from the USA to collect adults for a captive breeding effort even before the dam was built. This effort is now yielding positive results: after a decade of captive breeding, the erection of an artificial sprinkler system for habitat restoration, and experimental releases (Vandvik et al., 2014), nearly 10,000 toads were released to their former range in May 2018 (Anon, 2018).
Safeguarding a well-represented sample of the world’s biodiversity play only a small role in ex situ conservation efforts. Maintaining self-sustaining wildlife populations under human care not only reduce the need to collect individuals for research from the wild; it also allows researchers to study aspects such as physiology, genetics, and demographics of threatened species (Conde et al., 2019) using methods that might not be possible without animals in captivity. These studies can then provide knowledge and experience to help protect both ex situ and in situ populations. For example, the establishment of the Demographic Species Knowledge Index (Conde et al., 2019), summarise demographic data obtained from ex situ conservation facilities, play a crucial role in filling gaps in datasets for population viability analyses (Section 9.2) Ex situ facilities also play a critical role in captive breeding, head-starting, public outreach, education, and fundraising for in situ conservation. Many ex situ facilities have also become directly involved—and sometimes even taking leading roles—in field conservation efforts (Wilson et al., 2019). Lastly, many ex situ facilities directly connect conservation to social and economic progress through off-site education, employment, and implementation of a range of different community development activities (Ferrie et al., 2013).
Recent efforts to increase knowledge transfer among ex situ facilities has greatly enhanced their contribution to overall conservation efforts. Facilitated by organizations such as the IUCN’s Conservation Planning Specialist Group (CPSG), ex situ facilities now regularly share information on best practices for care and handling of species in human care, including aspects such as nutritional requirements, optimal housing conditions, and veterinary techniques to anaesthetize, immobilise, and reduce stress for animals when they are being moved or during medical treatments (see http://www.cpsg.org ). Much of this information is stored in a central database called the Zoological Information Management System (ZIMS). Maintained by Species360, ZIMS keeps track of animal husbandry, medical, and breeding information on over 6.8 million animals belonging to more than 21,000 species for over 1,000 member institutions in 90 countries. Ex situ facilities that maintain these records and comply with operations standards in animal welfare, conservation, education, and research can also apply to become an accredited institution with the Pan-African Association for Zoos and Aquaria (PAAZA), or its parent organization, the World Association of Zoos and Aquariums (WAZA). As of mid-2019, four Sub-Saharan African ex situ facilities were accredited by WAZA, and 19 by PAAZA.
Types of ex situ facilities
Many types of facilities help to preserve ex situ populations. Here we describe some of the most common, including zoos and aquaria for animals, and botanical gardens and seed banks for plants.
Ex situ conservation facilities compliment field conservation efforts through captive breeding, public outreach, education, knowledge generation, and fundraising.
Zoos around the world currently contribute to the conservation of nearly 7,000 species of terrestrial vertebrates (mammals, birds, reptiles, and amphibians) by caring for more than 500,000 individual animals. They do not do this alone; they often work with government agencies, universities, and a variety of other organizations who use zoo animals for research, education, and other conservation activities. While zoos traditionally focussed on displaying charismatic animals that draw visitors, many zoos are now also investing in the conservation of small threatened vertebrates, as well as invertebrates, such as butterflies, beetles, dragonflies, spiders, and molluscs (many of which are also cheaper to maintain). South Africa’s National Zoological Gardens, which houses more than 9,000 individual animals belonging to 705 species, is Africa’s largest zoo by variety of captive species and individuals. The zoo also hosts a variety of daily school programs meant to inspire kids to a career in conservation; these include holiday courses, a zoo club, and guided tours at night.
Aquaria are the aquatic version of zoos, specialised in caring, displaying, and conserving marine and freshwater biodiversity, such as fishes, corals, molluscs, and crustaceans (Figure 11.14). One such institution is South Africa’s uShaka Marine World, the world’s fifth largest aquarium and home to more than 390 marine species—most from the Western Indian Ocean—held in 11 million litres of seawater. Most organisms currently in aquaria have been obtained from the wild, but conservationists are constantly refining techniques to breed more species in captivity to limit wild collecting. Recent and dramatic increases in aquaculture, which currently accounts for roughly a third of fish and shellfish production globally, have made ex situ conservation of aquatic species even more important. The hope is that these ex situ populations will help maintain genetic stocks and act as insurances against disease outbreaks introduced by domestic fish, molluscs, and crustaceans.
Botanical gardens (and arboretums, which specialise on trees and other woody plants) are dedicated to the collection, cultivation and educational curation of living plant species. Botanical gardens across the world house more than 6 million living plants, representing over 80,000 species—approximately 25% of the world’s vascular flora (Wyse Jackson, 2001). The world’s oldest and largest botanical garden—the Royal Botanic Gardens in London, UK—maintains over 28,000 plant taxa, nearly 10% of plant taxa in the world. In Sub-Saharan Africa, there are at least 153 botanical gardens in 33 countries, which range from small community-organised centres to world-famous conservation hubs, such as South Africa’s Kirstenbosch Botanical Garden. Like zoos and aquaria, botanical gardens play a critical role in conservation efforts through public outreach and education. For example, Ghana’s Aburi Botanical Garden established a model medicinal plant garden where the public can gain first-hand knowledge on how to combine conservation, cultivation, and sustainable use of medicinal plants (Gillett et al. 2002).
A few botanical gardens and research institutes have developed collections of seeds, known as seed banks, which take advantage of the fact that seeds of most plants can survive for long periods when stored in cold, dry conditions. The seeds deposited in seed banks may be obtained from the wild, or from cultivated specimens. When gathering material from the wild, botanists generally target populations from across a species’ geographical and habitat ranges so their collections can capture as much of each species’ genetic diversity as possible. In this way, seed banks play a crucial role not only in conservation of plant species richness, but also genetic diversity. Seed banks may even be the only means some plant species are protected. Because many seeds of each species are usually collected, seed banks also provide a convenient opportunity for translocation projects. That is because safeguarded seed collections can be used to propagate not just large numbers of seedlings but, in some cases, custom-developed genetic mixtures to maximise local adaptations. The world’s largest and most diverse seed bank is the Millennium Seed Bank, UK. At the end of 2018, the Millennium Seed Bank catalogued over 2.25 billion seeds from over 39,000 species; its billionth seed, from an African bamboo, was deposited in April 2007. In addition to safeguarding a portion of plant diversity, the Millennium Seed Bank has also benefitted countries, such as Botswana, Burkina Faso, and Mali through the redistribution of banked seeds to aid ecological restoration efforts.
Seed banks contribute to conservation of genetic diversity of plants by collecting material across target species’ geographical and habitat ranges.
Challenges facing ex situ facilities
While the contribution of ex situ conservation facilities to overall biodiversity conservation strategies is significant (Conde et al., 2011), there are some drawbacks that need to be considered. For example, due to the limited number of individuals that can be maintained under human care, especially for larger animals, there is an increased risk that captive populations may suffer from threats facing small populations, such as inbreeding depression and demographic stochasticity (Section 8.7). There is also a concern that ex situ conservation can contribute to hybridisation concerns, for example if different cryptic species are accidentally managed as a single species. To avoid these threats, many ex-situ facilities manage their captive populations jointly as a single interbreeding metapopulation. They do this through studbooks which track the origin, pedigree, and demographic history of each individual in participating facilities. By maintaining and referring to these studbooks, ex situ conservation facilities can make informed decisions regarding transfer and breeding recommendations. The establishment of a European studbook for African dwarf crocodiles (Osteolaemus spp.) even addressed concerns about potential hybridisation between cryptic species (Schmidt et al., 2015).
Ex-situ facilities often manage captive populations as a single metapopulation using studbooks to track the origin and demographic history of breeding individuals .
Funding also remains an obstacle, given that ex situ facilities typically require large, long-term, funding commitments, in comparison to many in situ conservation activities. One consequence of funding limitations is that ex situ facilities mostly focus on showy or charismatic species that attract visitors, so small and less charismatic species are not always afforded equal protection (Brooks et al., 2009). Many ex situ facilities are also more inclined to house non-threatened species that are easier and less costly to care for, rather than threatened species with specialised needs (Table 11.1). For example, despite the fear of looming mass amphibian extinctions due to a disease caused by the chytrid fungus (Batrachochytrium dendrobatidis) (Alroy, 2015), 75% of ex situ amphibian collections consist of non-threatened species, with only 6.2% of all threatened amphibians afforded ex situ protection (Dawson et al., 2016). Neglecting threatened species in ex situ conservation efforts also creates a feedback loop, by maintaining a limited understanding on how to care for the species most in need.
|
Mammals |
Birds |
Reptiles |
Amphibians |
Total |
|
|---|---|---|---|---|---|
|
Worldwide a |
659 (55%) |
1,470 (65%) |
197 (27%) |
44 (5%) |
2,370 (47%) |
|
Africa |
110 (9%) |
234 (10%) |
34 (4%) |
6 (1%) |
384 (8%) |
|
Asia |
136 (11%) |
327 (14%) |
22 (3%) |
2 (0%) |
487 (10%) |
|
Oceania |
37 (3%) |
61 (3%) |
6 (1%) |
1 (0%) |
105 (2%) |
|
Europe |
191 (12%) |
465 (20%) |
73 (10%) |
19 (2%) |
748 (15%) |
|
North America |
145 (12%) |
311 (14%) |
53 (7%) |
14 (2%) |
523 (10%) |
|
South America |
40 (3%) |
72 (3%) |
197 (27%) |
44 (5%) |
353 (7%) |
|
Threatened species b |
45 (23%) |
42 (20%) |
22 (21%) |
8 (4%) |
117 (16%) |
|
Extinct in the Wild |
1 (100%) |
0 (0%) |
0 (0%) |
1 (100%) |
2 (100%) |
|
Critically Endangered |
7 (26%) |
4 (19%) |
5 (25%) |
3 (5%) |
19 (15%) |
|
Endangered |
13 (16%) |
12 (15%) |
2 (5%) |
3 (3%) |
30 (10%) |
|
Vulnerable |
24 (27%) |
26 (23%) |
15 (33%) |
1 (2%) |
66 (23%) |
|
CITES-listed species c |
95 (50%) |
121 (62%) |
45 (25%) |
1 (6%) |
262 (45%) |
|
Appendix I species |
30 (58%) |
4 (44%) |
8 (80%) |
1 (6%) |
43 (49%) |
|
Appendix II species |
58 (44%) |
112 (62%) |
37 (22%) |
0 (0%) |
207 (43%) |
|
Appendix III species |
7 (100%) |
5 (100%) |
0 (0%) |
0 (0%) |
12 (100%) |
Source: https://zims.species360.org , current as of April-2019. Compiled by Johanna Staerk (Species360).
Fortunately, ex situ facilities have responded to these concerns by developing several innovative mechanisms that enables them to contribute more to the conservation of threatened species. For example, ex situ facilities all agree that attracting more visitors attracts more funding. To attract more visitors, zoos and aquaria are increasingly keeping animals in enclosures that are representative of their natural environments; this keeps the animals heathier and providing more opportunities to exhibit natural behaviors which, in turn, leave visitors more satisfied. Some zoos and aquaria have also established special displays where visitors can feed, touch, or otherwise interact with animals. Many ex situ facilities have also started inviting local artists to display sculptures and other artwork, which adds to the experience for visitors and attracting people that might not otherwise have visited. A rather unusual—but very successful—attempt to increase foot traffic comes from the USA, where the California Academy of Sciences hosts dance parties with laser shows, food, and drinks every Thursday night ( http://www.calacademy.org/nightlife ), which visitors can enjoy while visiting the Academy’s aquarium and other conservation exhibits.
While the contribution of ex situ facilities to species conservation is significant, many rare species are ill-suited for ex situ efforts. Some species simply do not adapt or reproduce in captivity, while others that do relatively well in captivity experience behavioral and physiological changes or acquire diseases (Brossy et al., 1999) that prevent releases in the wild. Even so, the conservation biologists working at ex situ facilities constantly try to find ways to overcome these challenges. For example, staff at ex situ facilities sometimes use assisted reproductive techniques such as artificial incubation of bird and reptile eggs, or artificial insemination (Box 11.4) to overcome reproductive challenges (e.g. if individuals cannot mate because they are in different locations). Others use cryopreservation and genome resource banks for the long-term storage of embryos, eggs, sperm, or purified DNA, at least until those tissues can be used to increase a species’ genetic diversity, or perhaps even to resurrect an extinct species (see de-extinction, Section 8.8). However, many ex situ conservation techniques are difficult and expensive to implement. When possible, it is almost always preferable to preserve species in situ where they can be self-sustaining, free from inbreeding, and an interactive participant of their community and ecosystem.
Morné de la Rey
Embryo Plus,
Brits, South Africa.
A few centuries ago, Earth’s wildernesses enabled animals to roam and breed relatively freely. Today, sprawling cities, agriculture, and fences not only restrict animals’ ability to forage, but also limit reproduction between differing gene pools. These stresses create smaller and more isolated populations which are being edged toward extinction.
There are several landscape-scale conservation initiatives to counteract these imbalances. But some species and populations are so rare that they depend on intensive management to remain viable. Assisted reproductive techniques (ART) provide promise for helping such species. Over the past 30 years, ARTs have greatly enhanced how the livestock industry preserve, improve, and proliferate genetic stock. Now, efforts are also underway to use ARTs to ensure the preservation of biodiversity.
The many types of ARTs
ARTs include a wide array of medical procedures to address infertility, and to make reproduction possible between individuals unable to do so naturally (e.g. animals in different protected areas). In this way, biologists can ensure genetic exchange while eliminating the risks inherent in translocation such as spread of diseases, adaptation to new environments, and disruption of group dynamics.
ARTs have various levels from relatively simple to very complex. The most basic technique is artificial insemination. A major advantage of this technique is that it can multiply male genetic contributions by inseminating more females than would be possible in nature. Much progress has also been made in improving viability of cryopreserved semen to overcome challenges with timing of female reproductive cycles and other logistical constraints.
As for multiplying female genetic contributions, methods involve embryo transfer and in vitro fertilisation (IVF). With multiple ovulation embryo transfer (MOET) egg fertilisation occurs naturally; with IVF, it occurs in a laboratory incubator. In both cases, an embryo is eventually transferred to a surrogate mother which will carry it until birth. Scientists are currently working on improving viability of stored germplasm, so that embryos can be cryopreserved until a suitable surrogate mother is ready.
The third technique is nuclear transfer, also known as cloning. This very delicate procedure involves replacing the haploid DNA of an unfertilised egg with diploid DNA of another; cells are then cultured, after which the embryo is transferred to a surrogate mother.
Using ARTs to save the northern white rhino
Once widespread across Central Africa, poaching has pushed the northern white rhinoceros (Ceratotherium simum cottoni, EW) to the brink of extinction. Today, only two females remain, both in a semi-captive setting at Ol Pejeta Conservancy, Kenya. Incapable of natural reproduction, this species is committed to extinction without drastic intervention.
A cutting-edge initiative is currently underway to use ARTs to save this iconic species. While the project’s exact trajectory is still being developed, likely steps include optimising procedures for harvesting, maturing, and fertilising eggs, followed by embryo transfer into surrogate southern white rhinoceros. Some preliminary successes have also been achieved to generate stem cells from skin biopsies (Ben-Nun et al., 2011), which could be used in cloning. Genetic material (tissue samples and semen) of several northern white rhinos has been cryopreserved at various places around the world. However, there is a limited amount of sperm available (there are no males left), and so artificial insemination and IVF with northern white rhinoceros depends on embryo transfer successes. Many partners have been assembled to pool resources and ideas in support of this initiative, including Ol Pejeta Conservancy, Embryo Plus, Fauna & Flora International (FFI), Back to Africa, Dvur Karlove Zoo, Leibniz-IZW, Avantea, San Diego Zoo, and Kenya Wildlife Service.
Refining ARTs on other species
Before ARTs are implemented on the near-extinct rhinoceros, it is advisable to optimise procedures on another species. A logical choice would be the closely related southern white rhinoceros (C. simum simum, NT). However, the southern subspecies is also threatened, so we should look for more common mammals first.
Veterinarians at Embryo Plus routinely perform ARTs on domestic cattle, so efforts are currently focussed on building from this experience to work with wild bovines (Figure 11.D). For example, Embryo Plus recently produced the world’s first African buffalo (Syncerus caffer, NT) through IVF; the healthy calf named Pumelelo (meaning success in isiZulu) was born in June 2016. Embryo Plus has also produced several western Zambian sables (Hippotragus niger kirkii) from southern sable (H. niger niger) surrogates using embryo transfer. Plans are also underway to investigate the viability of using eland (Tautragus oryx, LC) and domestic horses (Equus ferus) as surrogate mothers for mountain bongo (T. eurycerus isaaci, CR) and Grevy’s zebra (E. grevyi, EN), respectively.
From dream to reality
The long-term objective of the northern white rhinoceros project is to establish a viable breeding herd which can be reintroduced into secure habitats. But much work remains for this dream to become reality. While there was one successful attempt in producing a healthy bongo calf by transferring an embryo to an eland mother (Woolf, 1986), inter-species embryo transfer remains challenging. Due to a rhinoceros’ size, we also need to ensure ART procedures can be performed safely without placing undue stress on the patient. Lastly, because each species’ embryos have different requirements in the laboratory, extensive research is necessary before ARTs can be attempted on a new species.
Although ARTs in wildlife management is still in its infancy, we are confident that early breakthroughs hold promise for the survival of the northern white rhinoceros, as well as other threatened species that may one day benefit from these procedures.