PAG 3 Sampling Techniques

Question 1

Describe random sampling and give one advantage and one limitation (3)

Answer 1

• In random sampling, sites are chosen using random coordinates (e.g. random numbers).
• Advantage: prevents selective sampling, reducing bias. accurate and representative data
• Limitation: some habitats may be under-sampled, leading to inaccurate biodiversity estimates

Question 2

Describe stratified sampling and give one advantage and one limitation (3)

Answer 2

Habitat is divided into distinct groups, and each is sampled separately.

• Advantage: ensures all habitat types are sampled, including small populations.
• Limitation: may over-represent small or distinct areas

Question 3

Describe opportunistic sampling and give one advantaged and one limitation (3)

Answer 3

• Researcher selects sites based on prior knowledge or areas of interest.
• Advantage: quicker and easier than random sampling.
• Limitation: high risk of bias, noticeable species may be over-recorded.

Question 4

Describe systematic sampling and give one adv and one limitation (3)

Answer 4

Samples taken at regular intervals (e.g. every 5 m along a transect).

• Advantage: good for detecting changes in biodiversity across a gradient.
• Limitation: may miss species not occurring along the transect

Question 5

Describe the methods for calculating species diversity using random sampling (6)

Answer 5

1. Select a suitable sampling area.
2. Place two tape measures at right angles to mark a grid.
3. Generate random coordinates for sample locations.
4. At each location, place the quadrat and identify species using a key.
5. Record abundance and percentage cover for each species.
6. Repeat at least 10 times, then calculate Simpson’s index

Question 6

Define species diversity and give the formula for Simpsons index of diversity

Answer 6

• Species diversity: The number of different species in a community.
• Formula: D = 1 - Σ(n/N)²
• Where N = total number of organisms of all species and n = total number of organisms of one species.

Question 7

Define species abundance and species distribution (2)

Answer 7

• Species abundance is the amount of a particular species present in a specific habitat.
• Species distribution is the locations where a species is found across an area.

Question 8

Describe the method for calculating species abundance (3)

Answer 8

1. Follow steps 2-6 from the species diversity method.
2. Multiply the sample abundance to estimate total population size.
3. Plot a graph of abundance for different areas.

Question 9

Describe the method for calculating species abundance and distribution using a transect (4)

Answer 9

1. Lay a tape measure along the sampling area.
2. Place quadrats at fixed intervals (e.g. every 5 m).
3. Record species identity and percentage cover in each quadrat.
4. Plot a graph of distribution against distance along the transect