Our Environment - Mining and the Environment: From Ore to Metal - page 306

It follows from this definition that biodiversity applies at different levels, namely:

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Ecosystems, which include a diversity of

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Habitats, each of which supports an assemblage or community of plant and animal

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Species, each of which includes individuals, each with their own unique set of

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Genes.

Any significant change in conditions, whether natural or man-made, has the potential to
reduce biodiversity at one or more of these levels. The geological record contains numer-
ous examples of events that caused sudden or progressive loss of biodiversity. Examples of
the former include the impact of large meteors; the extinction of the dinosaurs is commonly
attributed to such an event. Examples of the latter include climate change, which among
other effects has caused a succession of 'ice ages' during which glaciers have advanced
over major portions of the Earth's surface. However, although these events may have been
catastrophic at the time, the palaeontological record also indicates that each drastic loss of
biodiversity is followed by a major and, in geological terms, rapid evolution of new spe-
cies. It is as if the creation of new areas available for colonization provides the impetus for
renewed competition, involving rapid adaptation and a proliferation of new species.
In recent years, there have been numerous predictions of impending loss of biodiversity
as a result of man's activities. Case 7.4 is typical of the more extreme predictions. Many
practising biologists consider these predictions to be extreme as they are based on ques-
tionable assumptions.

Biodiversity in Relation to Biogeography

To evaluate biodiversity in perspective, it is also instructive to consider bio-geography,
the branch of biology that deals with the geographic distribution of plants and animals.
Accordingly, the Earth's surface can be divided into bio-geographic provinces, representing
areas defined by the endemic species present. The world's continents include many large
biological provinces of relatively uniform biological conditions. This is particularly the

To evaluate biodiversity in
perspective, it is also instructive
to consider bio-geography.

CASE 7.4
Human Threats to Biodiversity

In 1995 the United Nations Environmental
Program (UNEP) estimated the number of
known species to be 1,750,000. Annually
about 12,000 new species are added. Only
a fraction of all species is currently known.
Estimates say that the total number of species
may be as high as 10 or even 100 million.
The global variety of life varies according
to the different biospheres. Tropical rainforests
which cover only 7% of the world's land sur-
face host up to 90% of all terrestrial species.
More recent studies indicate that there are
areas on Earth which have a special signifi -
cance because of their great biodiversity. These

'Hot Spots' represent only 1.4% of the Earth's
surface, but are especially important because
they host 44% of all plant species and 35% of
all vertebrates.
Some estimates predict that the loss of
species in the next 50 years will be between
10% and 50% of the total number of species
that ever existed on Earth and that between
70 and 300 species disappear every day. The
current rate of extinction is said to be 50
to 100 times higher than extinction due to
natural factors.

Source: The Lutheran World Federation 2003