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The human world population in 1987 was 5000 million
The population of the United Kingdom is about 57 million

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A population is the number of individual of a particular
species in an area
This area can be large or small

The world human population was about the same (or stable)
for hundreds of years
Since the beginning of the last century it has risen sharply
Reason for this rise…

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Competition for resources (the amount of food, water and
shelter available to each individual)
Death rate (the number of individuals killed by predators
or disease

Successful organisms are able to increase their populations
relative to their competitors

Predator and prey relationships

Populations of predator and prey depend on one another…

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Aphids (or greenflies) feed in garden plants, especially
Ladybirds feed on aphids
When the population of aphids goes up so does the
ladybird population after a short delay
The ladybird population depends on the aphid population


A parasite is an organism that feeds of another and a

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Mutualism (Symbiosis)

This is a relationship where both organisms benefit
e.g. a down fish and an anemone, the down fish gets
protection and the anemone loses its parasites

Sometimes two completely different plants and animals live
If both benefit from living together it is called symbiosis

Both the shark…

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The sea anemone protects the hermit crab by
camouflaging it from its enemies

Plant mutualism

e.g. pulses (peas, beans and clovers)
These have nodules on the roots, which contain bacteria,
which are able to convert nitrogen from the air into
soluble nitrates that the plant can use for growth


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