Biodiversity and Conservation - continued
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How do we Conserve Biodiversity?

There are two main ways to conserve biodiversity. These are termed ex situ (i.e. out of the natural habitat) and in situ (within the natural habitat)

 

Ex Situ Conservation - out of the natural habitat

(Species-based)

  • Zoos - These may involve captive breeding programmes,
  • Aquaria - research, public information and education
  • Plant Collections - breeding programmes and seed storage

 

ZOOS
AN01124_.wmf (24236 bytes) In the past, zoos were mainly display facilities for the purpose of public enjoyment and education. As large numbers of the species traditionally on display have become rarer in the wild, many zoos have taken on the additional role of building up numbers through captive breeding programmes.
Although comparatively far more invertebrates than vertebrates face extinction, most captive breeding programmes in zoos focus on vertebrates. Threats to vertebrate extinction tend to be well publicised (e.g. Dormouse, Panda). People find it easier to relate to and have sympathy with animals which are more similar to ourselves, particularly if they are cute and cuddly (at least in appearance, if not in fact!). Not many visitors to zoos are likely to get excited over the prospect of the zoo 'saving' a tiny beetle, which they can barely see, let alone spiders or other invertebrates which often invite horror rather than wonder. Vertebrates therefore serve as a focus for public interest. This can help to generate financial support for conservation and extend public education to other issues. This is a very important consideration, as conservation costs money and needs to be funded from somewhere.

The focus on vertebrates is not solely pragmatic. Many of the most threatened vertebrates are large top carnivores, which the world stands to lose in disproportionate numbers. Such species require extensive ranges to provide sufficient prey to sustain them. In many cases, whole habitats for these predators have all but disappeared. Some biased expenditure on their survival may therefore be justified.

Several species are now solely represented by animals in captivity. Captive breeding programmes are in place for numerous species. At least 18 species have been reintroduced into the wild following such programs. In many cases the species was actually extinct in the wild at the time of reintroduction (Arabian Oryx, Pere David Deer, American Bison). In some cases, all remaining individuals of a species, whose numbers are too low for survival in the wild, have been captured and the species has then been reintroduced after captive breeding (California Condor).

The role of zoos in conservation is limited both by space and by expense. At population sizes of roughly 100-150 individuals per species, it has been estimated that world zoos could sustain roughly 900 species. Populations of this size are just large enough to avoid inbreeding effects. However, zoos are now shifting their emphasis from long-term holding of species, to returning animals to the wild after only a few generations. This frees up space for the conservation of other species.

Genetic management of captive populations via stud records is essential to ensure genetic diversity is preserved as far as possible. There are now a variety of international computerised stud record systems which catalogue genealogical data on individual animals in  zoos around the world. Mating can therefore be arranged by computer, to ensure that genetic diversity is preserved and in-breeding minimised (always assuming the animals involved are prepared to co-operate).

Research has led to great advances in technologies for captive breeding. This includes techniques such as artificial insemination, embryo transfer and long-term cryogenic (frozen) storage of embryos. These techniques are all valuable because they allow new genetic lines to be introduced without having to transport the adults to new locations. Therefore the animals are not even required to co-operate any longer. However, further research is vital. The success of zoos in maintaining populations of endangered species is limited. Only 26 of 274 species of rare mammals in captivity are maintaining self-sustaining populations (World Resources Institute).

Reintroduction of species to the wild poses several different problems.

  • Diseases
    The introduction of new diseases to the habitat, which can decimate existing wild populations. Alternatively, the loss of resistance to local diseases in captive-bred populations.
  • Behaviour
    Behaviour of captive-bred species is also a  problem. Some behaviour is genetically determined and innate, but much has to be learned from other adults of the species, or by experience. Captive-bred populations lack the in situ learning of their wild relatives and are therefore at a huge disadvantage in the wild. In one case of reintroduction, a number of monkeys starved because they had no concept of having to search for food to eat - it had always been supplied to them in captivity. In the next attempt, the captive monkeys were taught that they had to look for food, by hiding it in their cages, rather than just supplying it. 
  • Genetic Races
    Reintroduced populations may be of an entirely different genetic make-up to original populations. This may mean that there are significant differences in reproduction habits and timing, as well as differences in general ecology. Reintroduction of individuals of a species into an area where the species has previously become extinct, is in many cases just like introducing a foreigner. The Large Copper Butterfly is a good example of this. Although extinct in Britain, it persists in continental Europe. There have been over a dozen attempts to re-establish it in Britain over the last century, but none have been successful. This is probably due to the differing ecology of the introduced races. Replacement of extinct populations by reintroduction from other areas may not therefore be an option.
  • Habitat
    The habitat must be there for reintroduction to take place. In many cases, so much habitat has been destroyed, that areas must first be restored to allow captive populations to be reintroduced. Suitable existing habitats will also (unless the species is extinct in the wild) usually already contain wild members of the species. In this case, it is likely that within the habitat, there are already as many individuals as the habitat can support. The introduction of new individuals will only lead to stress and tension as individuals fight for limited territory and resources such as food. In this case, nothing positive has been accomplished by reintroduction, it has merely increased the stress on the species. It may even in some cases result in a decrease in numbers. In contrast, the provision of additional restored habitat nearby can allow wild populations to expand into it without the need for reintroduction.

 

AQUARIA

The role of aquaria has largely been as display and educational facilities. However, they are assuming new importance in captive breeding programmes. Growing threats to freshwater species in particular, are leading to the development of ex situ breeding programmes. The World Conservation Union (IUCN) is currently developing captive breeding programmes for endangered fish. Initially this will cover those from Lake Victoria in Africa, the desert fishes of N. America and Appalachian stream fishes. Natural habitats will be restored as part of the programme.

Marine, as well as freshwater species are also the subject of captive breeding programmes. For example, The National Marine Aquarium, in South West England, is playing an important role in the conservation of sea horse species through their captive breeding programme.  wpe118.jpg (5512 bytes)

PLANT COLLECTIONS
flower10.wmf (7980 bytes) Populations of plant species are much easier than animals to maintain artificially. They need less care and their requirements for particular habitat conditions can be provided more readily. It is also much easier to breed and propagate plant species in captivity.
There are roughly 1,500 botanic gardens world-wide, holding 35,000 plant species (more than 15% of the world’s flora). The Royal Botanic Gardens of England (Kew Gardens) contains an estimated 25,000 species. IUCN classifies 2,700 of these as rare, threatened or endangered. Many botanic gardens house collections of particular taxa which are of major conservation value. There is however, a general geographic imbalance. Only 230 of the world’s 1,500 gardens are in the tropics. Considering the greater species richness of the tropics, this is an imbalance that needs to be addressed.

A more serious problem with ex situ collections involves gaps in coverage of important species, particularly those of significant value in tropical countries. One of the most serious gaps is in the area of crops of regional importance, which are not widely traded on world markets. These often have recalcitrant seeds (unsuited to long-term storage) and are poorly represented in botanic collections. Wild crop relatives are also under-represented. These are a potential source of genes conferring resistance to diseases, pests and parasites and as such are a vital gene bank for commercial crops.

Plant genetic diversity can also be preserved ex situ through the use of seed banks. Seeds are small but tough and have evolved to survive all manner of adverse conditions and a host of attackers. Seeds can be divided into two main types, orthodox and recalcitrant. Orthodox seeds can be dried and stored at temperatures of -20oC. Almost all species in a temperate flora can be stored in this way. Surprisingly, many tropical seeds are also orthodox. Recalcitrant seeds, in contrast, die when dried and frozen in this manner. Acorns of oaks are recalcitrant and it is believed that so are the seeds of most tropical rain forest trees.

The result of storing seeds under frozen conditions is to slow down the rate at which they lose their ability to germinate. Seeds of crop plants such as maize and barley could probably survive thousands of years in such conditions, but for most plants, centuries is probably the norm. This makes seed banking an attractive conservation option, particularly when all others have failed. It offers an insurance technique for other methods of conservation.

All of the ex situ conservation methods discussed have their role to play in modern conservation. Generally, they are more expensive to maintain and should be regarded as complementary to in situ conservation methods. For example they may be the only option where in situ conservation is no longer possible.

 

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Copyright 2003 Dr Barbara Corker

 

 

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