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Populations
1.1 Populations and ecosystems
Ecology is the study of inter-relationships between organisms and their
environment.
Abiotic ­ non-living components (Rain, Temperature)
Biotic ­ living components (Organisms, Competition)
Biosphere ­ layer of land, air and water that surrounds the earth
Ecosystems and self-contained functional units, Two major components;




AQA Biology…

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Flow of energy
Cycling of elements
Population ­ group of interbreeding organisms of a species in a habitat
Boundaries of a population can be difficult to define
Populations of different species make up a Community
A community can be defined as all the populations of different species living or
interacting…

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Niche ­ describes how an organism fits into its environment
Niche refers to where the organism lives and what it does there (Predator or
producer)
No two species can occupy the same niche
1.2 Investigating Populations
To study a habitat you need to count the number of species in a…

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Number of quadrats in the study area ­ larger number will give more reliable
results but recording can be time consuming. Balance needed between the
time and the validity. Greater number of species being recorded the greater
number of quadrats needed to get valid results.
Position of each quadrat within…

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Obtain a series of coordinates by using random numbers taken from table or
generated by a computer.
Place quadrat at the intersection of each pair of coordinates and record
species within.
More informative to measuse abundance systematically rather than randomly.
Stages of zonation shown well when using transects
Line transect…

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Frequency ­ likelihood of particular species appearing in the quadrat. Gives a quick
idea of species present. Doesn't provide information about density or distribution
Percentage cover ­ estimate of area within quadrat that particular plant/species
appears. Useful when abundance is difficult to count. Data collected rapidly. Less
useful when species…

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Estimate population size = total number of individuals on first sample x total number
of individuals in second sample/ number of marked individuals recaputed
Proportion of marked to unmarked is second sample is same as proportions of
marked to unmarked as a whole population
Marked individuals released first distributed themselves…

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Data has to be analysed and interpreted.
Present the data in form of table or graph
1.3 Variations in population size
Population is a group of interbreeding individuals of the same species in a habitat
Number of individuals in the population is the population size
A period of slow growth…

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A period population growth declines, its size remains stable. Due to food supply
limiting factors.
Many factors affect the overall size of the population. Changes in factors change the
overall size.
Abiotic factor ­ concerned with the non-living part of environment
Biotic factor ­ concerned with the activities of living…

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supported. Plants and cold-blooded animals, below optimum temp enzymes
work slower and metabolic rate slows. Temp to high, enzymes denature
population grows slower. Warm blooded animals can maintain a constant
temperature. Further temperature gets from optimum more energy
organisms use to keep normal body temperature. Leaves less energy for
growth…

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ali wasi

Excellent

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