A quadrat is a square frame used to isolate a sample area for ecological study. By randomly placing quadrats across a study site, scientists can estimate population sizes and measure biodiversity without counting every organism in the area.

1. Mark out the study area to be surveyed.
2. Use a random method to select coordinates, such as rolling dice for vertical and horizontal axes.
3. Place the quadrat at the chosen coordinates, ensuring consistent placement each time.
4. Identify and count all plants or slow-moving animals (e.g., snails, slugs) within the quadrat.
5. Repeat the sampling at least 25 times to improve reliability.
6. Use the counts to calculate an average number of organisms per quadrat.
7. Multiply the average by the total number of quadrats that could fit in the study area to estimate the population size.

Quadrats - p68 - BBA Science:

Using quadrats to estimate population and biodiversity - Margaret Clark:

📄 Classification and biodiversity – WJEC - BBC Bitesize: https://www.bbc.co.uk/bitesize/guides/z9q982p/revision/4

• Use quadrats of different sizes to compare effects on sampling accuracy.
• Apply the method to both plant species and slow-moving animals to contrast results.
• Combine quadrat sampling with a transect line to investigate how species vary across a habitat gradient.
• Compare random sampling with systematic sampling to discuss bias.

• Avoid disturbing or damaging plants and animals within the quadrat.
• Take care when working outdoors (sun protection, insect repellent, hydration).
• Watch for uneven ground to prevent trips and falls.
• Wash hands after handling soil or organisms.

• Why is random sampling important when using quadrats? (It prevents bias and ensures results are representative.)
• Why should many samples be taken rather than just one or two? (More samples improve accuracy and reliability.)
• How would the results change if quadrats were always placed in the same type of area? (It could bias the data, misrepresenting the true population.)
• How can quadrat data be used to estimate biodiversity in an ecosystem? (By recording the number and variety of species within quadrats, scientists can calculate species richness and diversity.)