sampling reading
This chapter covers Ecology and, as such, has a vocabulary all its own – which is often examined.
Environment: All the organisms (biotic) and the conditions (abiotic) which exist in an area
Abiotic factors: all the non-living factors in an environment, such as rainfall, temperature, soil.
Biotic factors: All the living organisms in an area – such as producers, predators and parasites.
Population: All the members of one species living in an area
Community: The total of all the populations living in an area (i.e. all the biotic factors)
Ecosystem: The community of living organisms and the abiotic factors affecting them in one area.
Habitat: The place where an organism lives
Niche: Where an organism fits into the community - covering feeding, nesting, and range of habitat.
Counting populations
Because it is impossible to count all the members of a large community, some form of sampling has to be used. The size of the sample depends on the area to be investigated, but can be shown on a graph as shown (right):
Beyond this point, more samples (= more work) does not increase the reliability of the results.
Ideal sample size
AQA are very keen that you should know the importance of random sampling. This is essential to avoid bias. In fieldwork, this is done by:
1. Lay out two tapes at right-angles
2. Use random number tables to pick co-ordinates
3. Place a quadrat (of suitable size) at that point and count the organisms within it
4. Repeat this process until enough samples have been obtained (30 or more)
5. The edge effect: What to do with plants which touch the edge? The rule is if they touch the right side or the top, count them "in". If they touch the bottom or the left side, count them "out".
Quadrats (= a frame of known size – typically 1m or ½m square, which may be divided into 100)
These can be used to estimate a population in an area which is fairly uniform. Examples include lawns, woods and open ground. They can produce three estimates of population size:
1.
Environment: All the organisms (biotic) and the conditions (abiotic) which exist in an area
Abiotic factors: all the non-living factors in an environment, such as rainfall, temperature, soil.
Biotic factors: All the living organisms in an area – such as producers, predators and parasites.
Population: All the members of one species living in an area
Community: The total of all the populations living in an area (i.e. all the biotic factors)
Ecosystem: The community of living organisms and the abiotic factors affecting them in one area.
Habitat: The place where an organism lives
Niche: Where an organism fits into the community - covering feeding, nesting, and range of habitat.
Counting populations
Because it is impossible to count all the members of a large community, some form of sampling has to be used. The size of the sample depends on the area to be investigated, but can be shown on a graph as shown (right):
Beyond this point, more samples (= more work) does not increase the reliability of the results.
Ideal sample size
AQA are very keen that you should know the importance of random sampling. This is essential to avoid bias. In fieldwork, this is done by:
1. Lay out two tapes at right-angles
2. Use random number tables to pick co-ordinates
3. Place a quadrat (of suitable size) at that point and count the organisms within it
4. Repeat this process until enough samples have been obtained (30 or more)
5. The edge effect: What to do with plants which touch the edge? The rule is if they touch the right side or the top, count them "in". If they touch the bottom or the left side, count them "out".
Quadrats (= a frame of known size – typically 1m or ½m square, which may be divided into 100)
These can be used to estimate a population in an area which is fairly uniform. Examples include lawns, woods and open ground. They can produce three estimates of population size:
1.