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Summary AQA A Level Biology (A2)- Population
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Full lesson and revision notes on the population topic in AQA A2 Biology.
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Interspecific CompetitionCompetition between members of different species for a resource or multiple resources. This is
competition for a resource between members of different populations in the same community. The
stronger competitor can utilise the resources best. The competing populations will grow slower than
if there wasn’t two different species competing for that resource – it may even lead to extinction of
the weaker competitor.
An example would be red squirrels vs. grey squirrels:
Grey squirrels arrived in Britain 130 years ago from
America.
Red Squirrels – They are seed eaters and forage in
trees. They spend little time on the forest floor.
Grey Squirrels – They are seed eaters and forage both
on the forest floor and in trees. They also eat bird eggs
and are more aggressive.
In addition, the preferred habitat of the red squirrels
has decreased whereas that of the grey squirrels has
increased.
This means that the grey squirrels can utilise the resources better as they will eat food from the floor
as well as the trees so there is more food available to eat. This means more energy for reproduction,
which then means more offspring so the population grows.
Intraspecific Competition
This is competition for resources between individuals from the same population. It causes the
population growth rate to slow down and has a greater effect the less plentiful the resource is. It is
more intense competition than interspecific competition as they are fighting for the same niche.
Predator-Prey Relationships
Population size of predators/prey are cyclical. The peak of populations of predators peak after prey.
Predators hunt and eat prey
Predator numbers increase
Prey numbers drop as they are eaten
More competition for prey as less prey available
Less prey eaten so predator numbers drop
Less prey eaten
Prey numbers increase
Less competition for prey and more prey available
Predators hunt and eat more prey
Prey numbers increase
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