Biodiversity (or biological diversity) is used to refer to the
variability among living organisms. By the definition used by
the Convention, 'biological diversity' means:
The
variability among living organisms from all sources, including,
inter alia terrestrial, marine and other aquatic ecosystems
and the ecological complexes of which they are a part; this
includes diversity within species, between species and ecosystems.
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The most
obvious differences are often those to be found between different
species. A species is a group of organisms that are sufficiently
similar to one another to be able to interbreed in nature and
produce fertile offspring. Each species has its own particular
specialisations to fit it to its own niche or place in the environment.
Through external changes (such as alterations in climate or decimation
of populations through predation or disease) or internal ones
(such as changes in genetic composition), many species have become
extinct. There are therefore far fewer species alive today that
there were in the past, and this loss of species (and therefore
of biodiversity) has accelerated in the past few hundred years
through the increasing impacts man has on the environment.
As indicated in the definition above, variation is also found within
species: each individual plant or animal has its own unique set
of genes and therefore its own unique characteristics. This uniqueness
allows each individual to interact with its environment in slightly
different ways from other individuals - it may need slightly more
or slightly less of some mineral, be more or less susceptible to
disease or poisons and so on.
When the numbers of individuals (i.e. the abundance) of a species
decreases, the total genetic variation within a species is also
usually reduced. The species is then less well able to cope with
changes in the environment and hence is more likely to become extinct
when a change occurs.
In addition to the two levels just mentioned, life on earth shows
great diversity within and between different ecosystems. Different
external conditions, habitats within each ecosystem and different
kinds of interactions between species in ecosystems mean that the
functioning, nature of resources provided, resilience to change
and the sustainability of exploitation of ecosystems all vary widely
even within broadly similar climatic regions. This provides the
third level of biological diversity.
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