Biodiversity and Conservation - continued
|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
Situ Conservation - out of the natural habitat
- Zoos - These may involve
captive breeding programmes,
- Aquaria - research, public information and education
- Plant Collections - breeding programmes and seed
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 is a
computerized International Species Inventory System (ISIS) which catalogues 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 inbreeding
minimized (always assuming the animals involved 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 more. 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.
Reintroduction of species to the wild poses
several different problems.
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
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
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) 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.
|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.
||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 worldwide, holding 35,000 plant species (more than 15% of the worlds
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 worlds 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.
Copyright 2003 Dr Barbara