Geoscience Reference
In-Depth Information
extinction, Myers listed eighteen hot spots considered to
have the highest conservation priority (
Figure 22.12
).
Of
the eighteen habitats, fourteen are tropical forests and four
are Mediterranean ecosystems. The list is likely to be the
very minimum, representing only those areas which are
well documented. There are likely to be many more 'hot
spots', especially in oceans, lakes and rivers, which will be
added in the near future. The IUCN also recognizes 250
Centres of Plant Diversity
(CPDs) which are particularly
rich in plant species and which would safeguard a high
proportion of the world's flora if they were to be
protected. In contrast to 'hot spots', though, CPDs are not
classed on the basis of threat of extinction.
Part of the awakened interest in global biodiversity is
undoubtedly economic as much as ethical in nature.
The world's food supplies depend upon about 200 plants
which have been domesticated, of which perhaps twenty
are of major economic importance. The development
of high-yielding varieties depends upon wild plants to
donate genetic material to the cultivars for needed
improvements, e.g. to improve resistance to pests and
diseases . Future breeding programmes will depend upon
the availability of wild plants. Similarly, there is enormous
potential among the plants of the world for medicinal use
and the extraction of new drugs. The World Health
Organization (WHO) lists 20,000 plants with medicinal
uses, of which only 25 per cent have been studied as
a source of new drugs. However, anthropologists and
ethnobotanists estimate that among the world's indigen-
ous peoples perhaps 50,000 to 70,000 plant species are
used for medicines; again, only a few have been studied
in detail and there is an urgent need to investigate them
before they become lost for ever through extinction. Given
the importance of biodiversity, it is not surprising that it
has been the subject of several important conservation
programmes. The
World Conservation Strategy
published
by the IUCN in 1980 brought the issue to centre stage. It
proposed that countries should develop national conser-
vation strategies, with biodiversity as one of several goals.
In 1992 in Rio de Janeiro the United Nations Conference
on Environment and Development (UNCED) proposed
a Biodiversity Convention which amounted to a global
strategy for maintaining biodiversity. In November 1995,
at a conference in Jakarta, Indonesia, it was decided that
Montreal, Canada, would be the home of
THREATS TO GLOBAL
BIODIVERSITY
The destruction of the world's vegetation is recognized as
one of the most serious of human impacts. An immediate
result is the extinction of plants and animals and the loss
of habitat. It is estimated that between 1990 and 2015
between 2 per cent and 10 per cent of the flora of tropical
forests will become extinct. Another threatened habitat is
oceanic islands, very often with their own endemic species
which are jeopardized by the introduction of competitive
foreign species. It is estimated that 30 per cent of plants
under threat of extinction are island endemics. About
1,000 plant species are known to have become extinct in
the past 2,000 years, and about 25,000 are threatened.
However, these estimates are likely to be on the low side,
given the lack of data for many regions.
The International Union for the Conservation of
Nature (IUCN) issues Red Data topics of threatened
species. In 1990 4,500 animal species were listed as
threatened; this figure represents 12 per cent of mammals,
11 per cent of birds, 4 per cent of fish, but only 0ยท1 per
cent of insects. The major threats to both plants and
animals are as follows:
1
Loss by grazing, arable farming, and settlement.
2
Over-exploitation for commercial gain and sport
hunting (
Plate 22.5
).
3
Deliberate or accidental introduction of competitive
species.
4
Deliberate eradication of pest species.
5
Disease.
Most of the threatened mammal and bird species live in
tropical countries or on oceanic islands. In the latter case,
flightless birds have suffered very badly from introduced
vermin like rats. In contrast, many threatened reptiles,
amphibians and fish live in temperate latitudes.
A special concern has been to protect entire ecosystems
rather than to concentrate on one or two species
within those ecosystems. About 20 per cent of all plants
are classed as
endemics
, i.e. plants with a very restricted
range and confined to a specific region. The island of
Madagascar, one of the most isolated of large islands, has
10,000 plant species, 80 per cent of which are endemic,
i.e. found nowhere else. It also has fifty species of lemurs
which are endemic too. The Mediterranean biome in
California contains 25 per cent of all plant species found
in North America, of which about 50 per cent are
found nowhere else in the world. On the basis of regions
which have unique species and which are threatened by
the UN
Convention on Biological Diversity.
CONCLUSION
Diversity and stability of ecosystems have become
important fields of study in biogeography as human
