Required Practical 9 - Field Investigation

What is random sampling?

Sampling technique in which each sample has an equal probability of being chosen.

How would you use random sampling to estimate the population size of a plant species?

• Create a grid of the area using tape measures.

• Use a random number generator to generate coordinates.

• Set down a quadrat at coordinates and record the number of required species within the quadrat.

• Repeat using many sampling sites.

• Estimate population size: (area sampled / total area) × number of plant species counted.

Why would you use a random number generator to determine coordinates?

To avoid bias and obtain representative results.

What is systematic sampling?

Sampling technique where there is a fixed, periodic interval between consecutive samples.

Describe how you would use continuous sampling to investigate the effect of an abiotic factor in the distribution of a plant species.

• Create a hypothesis on the effect of the change in an abiotic factor on the distribution of a plant species.

• Lay a tape measure along an area with an ecological gradient.

• Place a quadrat at the start and count the number of plants.

• Repeat at 5m intervals along the transect.

• Record the value of the abiotic factor (e.g., light intensity) at each sampling site.

• Produce a graph of plant numbers (y) against the abiotic factor (x).