Biodiversity
Biodiversity is the variety of different species of organisms which are living in an
ecosystem. The greater the number of different species the greater the biodiversity.
Having a large variety of different species within an ecosystem is important as this
makes the ecosystem more stable. Stability ensures that the ecosystem and the
species in it will survive over long periods of time.
This also ensures that when there are natural disasters e.g. forest fires, volcanic
eruptions although the biodiversity may be disturbed initially, there is a greater chance
of it returning to something like its original levels more quickly.
Importance of biodiversity
Biodiversity is important because:
Importance
Food
Genetic material
Medicines
Raw materials
Example
We obtain food from the wild (e.g. fish from north sea) and from
domestic species (e.g. cattle) descended from wild varieties.
We rely on wild varieties of species as a source of genetic material to
produce new species (e.g. disease resistant crops).
Many of our medicines come from plants (e.g. morphine from opium)
and there are many plants who’s medical uses have not yet been
discovered.
We get raw materials like timber and rubber from plants.
Biodiversity crisis
The world is currently experiencing a biodiversity crisis as the variety of species of
organisms in the world is decreasing. This is due to factors such as habitat
destruction, pollution and grazing.
Habitat destruction
Human activities such as agriculture, industry and construction have lead to destruction
of a large number of habitats.
 deforestation (clearing of forests) - rainforests are being cut down to clear
space for houses and farms. This destroys complex ecosystems which contain a
large variety of species.
 pollution - sulphur dioxide is a gas produced when fossil fuels are burned. This
gas destroys habitats by:
1. killing plants
2. causing acid rain which can destroy ecosystems like forests
 pollution - untreated sewage dumped in rivers and streams is fed on by bacteria
which use up all the oxygen and this kills other organisms in the river or stream.
Grazing
Animals grazing can have positive or negative affects on biodiversity depending on the
level of grazing.
Level of grazing
Affects on plants
Affects on biodiversity
Low
small number of vigorous grass species
dominate
Reduces biodiversity
Medium
variety of plants can survive
Maintains biodiversity
High
all plant species are damaged, some may
die out
Greatly reduces
biodiversity
Ecosystem stability
The greater the number of species in an ecosystem the more stable it is. Reductions
in biodiversity reduce the number of different species in ecosystems and
consequently the stability of ecosystems is decreasing.
Below are two food webs; ecosystem 1 - a woodland ecosystem with a large number of
different species
ecosystem 2 – a woodland ecosystem with a small number
of different species.
ecosystem 2
ecosystem 1
owl
fox
blue tit
caterpillar
leaves
hedgehog
snail
rabbit
grass
woodlice worm
owl
blue tit
caterpillar
leaf litter
The stability of these ecosystems can be seen if a species is removed.
tits were removed from the ecosystems the following would occur:
snail
leaves
If the blue
ecosystem 1 – owls would eat more rabbits and would survive
ecosystem 2 – the owls would die out as there is nothing else for them to eat
Ecosystem 1 is stable because the large number of species in it allows organisms to
cope with changes in individual populations.
Ecosystem 2 is unstable because the small number of species means that a change in
an individual population can have serious affects on other populations.