PAG 3: Sampling Flashcards
What is the purpose of random sampling? (1)
Used to sample a non-motile species over a large area to avoid bias
When is systematic sampling more appropriate than random sampling? (2)
When studying a non-motile species along an environmental gradient
To investigate the correlation between an abiotic factor and species distribution
What are examples of abiotic factors that can affect species distribution? (3)
Light intensity
Soil pH
Temperature
Describe the method for random sampling using quadrats. (5)
- Divide the map of the area into a grid
- Use a random number generator to select coordinates
- Place a quadrat at each coordinate
- Count individuals or estimate percentage cover
- Repeat with multiple quadrats and calculate the mean abundance
Describe the method for systematic sampling using a belt transect. (5)
- Place a tape measure along the environmental gradient
- Place quadrats at regular intervals along the transect
- Measure species abundance in each quadrat
- Measure the abiotic factor at each sample point
- Repeat with multiple transects and calculate the mean abundance
Why may percentage cover be used rather than frequency to determine the abundance of a particular species? (1)
The species is too small or too difficult to count individually
How would you determine the mean percentage cover for species X? (3)
Use a random number generator to determine quadrat positions
Use a large number of quadrats and only count a square if it is more than half covered by the species
Divide the total percentage cover by the number of quadrats to calculate the mean percentage cover
What is an advantage of using percentage cover rather than frequency? (1)
It is a faster way to investigate populations as you don’t need to count individual organisms
Why did the student use random sampling? (1)
It removes sampling bias
What are the limitations of using systematic sampling to estimate the population of species X in a field? (2)
Systematic sampling is not appropriate unless there is an environmental gradient
Transects run in one direction, but to cover the entire field, multiple transects would be needed in different directions
What is meant by an interrupted belt transect? (1)
Quadrats are placed at intervals along a transect, with space between the quadrats
What two factors should be considered when determining the size of a quadrat? (2)
The size of the species being investigated
The size of the area being studied
Why is it important to use a large sample size? (2)
It minimises the effect of anomalies
It ensures the sample is representative of the population
Which statistical test could be used to determine the relationship between abundance and an environmental factor? (1)
Spearman’s rank correlation coefficient
