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Populations and ecosystems
A population is all the organisms of one species in a habitat.
Populations of different species form a community.
An ecosystem is a system of organisms interacting with each other and their physical environment.
Ecosystems vary in size; a garden pond could be considered an ecosystem as could a rainforest.
A community is the sum of all organisms in an ecosystem.
Population-All the individuals of one particular species found in an ecosystem at any given time.…read more

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A critical appreciation of some of the ways in which the
numbers and distribution of organisms may be investigated.…read more

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Random sampling with quadrats and counting along transects to obtain quantitative data.
A suitable number of quadrats are placed on the ground at
different points across the area that you are investigating.
The species frequency is recorded in each quadrat.
The sample needs to be random so the results are valid.
The use of percentage cover and frequency as measures of abundance.
The use of mark­release­recapture for more mobile species.
A number of animals are caught, marked and then released back into the
community.…read more

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All fieldwork affects the environment
eg people walking around may cause
soil erosion.
Some people don't think its right to
damage the environment so
investigations should be planned to
restrict the impact on environment.…read more

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· appreciate the tentative nature of
conclusions that may be drawn from such data.
Variation in population size
Population size may vary as a result of
· the effect of abiotic factors
· interactions between organisms: interspecific and
intraspecific competition and predation.
Population size is dependent on the availability of resources. A key biotic factor is
competition for resources, there are two types of competition;
Intraspecific competition
Competition for resources such as food, water, breeding sites etc.…read more

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The prey population doesn't always increase; it just stops
decreasing so quickly. It only increases after
reproduction. This explains for both prey and predators
why there is a time lag between population decline and
ascent.…read more

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Human populations
Population size and structure, population growth rate, age-population pyramids
survival rates and life expectancy.…read more


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