Using Quadrats

• Quadrat


  A square frame enclosing a known area, e.g. 1 m²
• Using quadrats to study the distribution of small organisms


  1. Place a 1m² quadrat on the ground at a random point within the first sample area

  2. Count all the organisms within the quadrat

  3. Repeat steps 1 and 2 as many times as you can

  4. Work out the mean number of organisms per quadrat within the first sample area

  5. Repeat steps 1 to 4 in the second sample area

  6. Compare the two means
• If your quadrat has an area of 1 m, the mean number of organisms per m² is just the same as the mean number per quadrat
• Estimating the population size of an organism in one area

  1. Work out the mean number of organisms per m²

  2. Multiply the mean by the total area (in m²) of the habitat
• Population size


  Also called abundance
• Environmental variation affects the distribution of organisms
• Habitat


  The place where an organism lives, e.g. a playing field
• Distribution


  Where an organism is found, e.g. in a part of the playing field
• Where an organism is found is affected by environmental factors
• Example of distribution affected by environmental factors

  • Daisies are more common in the open than under trees, because there's more light available in the open
• Studying the distribution of an organism can be done by measuring how common it is in two sample areas and comparing them, or by studying how the distribution changes across an area</b>
• Both of these methods give quantitative data (numbers) about the distribution
• Example of using quadrats to study distribution

  • Anna counted the number of daisies in 7 quadrats within her first sample area and recorded the following results: 18, 20, 22, 23, 23, 23, 25
  • The TOTAL number of organisms was 154
  • The MEAN was 22 daisies per quadrat
• Students used a quadrat with an area of 0.5 m² to randomly sample daisies on an open field, finding a mean of 10.5 daisies per quadrat. The field had an area of 800 m². The estimated population of daisies on the field was 16,800