Using quadrats to sample

Aim

In this activity, students use quadrats to gather random data about biodiversity in small sections of the study area. A quadrat is a one-metre square measuring device. Students peg the quadrat on the ground. Then they use a 10-centimetre-square guide to record all the living things found within the quadrat's perimeter. The guide is fitted with 'cross-hairs' and the living things directly under the cross-hairs are recorded. Two options are offered. In option 1 (Step 2a), the entire quadrat is sampled systematically and students gather 100 sets of data. In option 2 (Step 2b), the quadrat is sampled randomly and students gather 10 sets of data.

Preparation

You will need:

• A one-metre-square quadrat. To make this, you can use a four-metre rope and mark it at 1, 2 and 3 metre intervals. Then arrange the rope around four pegs to form a square. Alternatively, you can use one-metre lengths of light wood or plastic rods joined at the corners to enclose a one-metre area.
• A 10-centimetre-square guide made of cardboard. This is fitted with threads across the diagonals of the inner square — these form the 'cross-hairs'.
• A reference chart of living things in the area. You prepared this in Step 4 of 'Setting up for success'.
• Pencils
• Quadrat data recording sheets (MS Word 36kb).

Before going into the field, students can practise recording data in an online activity.

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Process

Step 1 — Set up the quadrat for sampling

Working in groups of two or three, students randomly place a one-metre quadrat on the ground somewhere in the study area. The quadrat can be secured with pegs at each corner to minimise movement.

Step 2a — Systematic sampling for 100 sets of data

Starting in the top left corner, place the 10-centimetre square guide within the quadrat. Record the living thing directly beneath the cross-hairs. Progress across and down the quadrat as if reading, until all the living things found beneath the cross-hairs are recorded on the data sheet. Collect a sample, take a photograph or do a drawing of each living thing so that you can identify it later.

Step 2b — Random sampling for 10 sets of data

Randomly place the 10-centimetre square guide in ten places within the quadrat. Mark each place with a brightly coloured marker so that it is not repeatedly sampled. Record the living things found beneath the cross-hairs. Collect a sample, take a photograph or do a drawing of each living thing so that you can identify it later.

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Step 3 — Compare data

After each quadrat has been catalogued, compare the data collected by all the groups. Discuss common data, unique data and the variety in biodiversity.

Biodiversity varies from place to place — this is called 'variation over distance'. Variations between years or seasons are called 'variations over time'. Biodiversity changes over distance and time.

Step 4 — Identify new specimens

Identify any new specimens that were found. Give them a code and then enter them in the reference chart.

Reporting

Data can be processed in a frequency distribution table. A bar graph can be generated and percentages calculated. A written report could identify patterns in the frequencies, provide explanations for these patterns and include predictions.

Research the status of the living things catalogued in the survey. Identify which are native, which are introduced and which behave as pests or weeds.