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Variation in Populations

Ecology:the study of the inter-relationships between organisms and their environment

Biosphere:the life supporting layer of land, air and water that surrounds the Earth

Ecosystem: more or less self-contained functional unit comprising of all the biotic and abiotic
features in a specific area

Population:a group of interbreeding organisms…

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Issues may arise where organisms are only partly within the quadrat. It
must be decided beforehand how these will be counted and the
decision reached must be carried out consistently throughout the
fieldwork.



Transects
It is sometimes more logical to measure abundance and distribution
using a systematic method, particularly where…

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Ethics

Where possible, the organisms should be studies in situ. If it is necessary to remove them,
the numbers taken should be kept to a minimum.
Any organisms removed should be returned to their original habitat, even if they're dead
A sufficient period of time should elapse before the site…

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Water and Humidity . Where water is scarce, populations are smaller and consist only of
species which are well adapted to living in such conditions. Humidity affects the
transpiration rate of plants and the evaporation of water from the bodies of animals.

Competition

Intraspecific competition: competition for resources between two…

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Social pressures and conditions . In some Countries, a large family improves social
standing.
Contraception . The use of birth control is banned in some countries while in others it is
expensive/difficult to acquire
Political factors . Education, taxation, policies and incentives influence birth rates

Factors affecting death rate

Age…

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Survival Curves

Survival curves show the percentage of all individuals born in a population that're still alive at any
given age. They allow us to calculate life expectancy by simply reading off the graph the age at
which 50% survive.




Type I ­ long life expectancy with low infant mortality…

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