Required practical - measuring population size in a habitat

• Aim

  To measure the species richness on the school field in areas in which the grass is regularly and irregularly cut.
• Method

  1. choose a starting point on the school field in an area where the grass is often cut
  2. use random numbers to generate a set of coordinates to place your first quadrat
  3. count the number of different plant species within this quadrat (the species richness)
  4. return to your starting position and repeat steps two and three a further 14 times using different random numbers
  5. repeat steps one to four for a part of the school field which the grass is infrequently cut
  6. compare your results by calculating a mean for each location
• Measuring population size of a common species in a habitat

  1. Use random sampling with quadrats

  2. Place two 20m tape measures at right angles

  3. Select random numbers to determine quadrat placement

  4. Count number of organisms in each quadrat

  5. Estimate total population using formula
• Using sampling techniques to investigate the effect of a factor on the distribution of a species

  1. Place transect line from tree outwards

  2. Use quadrat to count organisms at each point along transect

  3. Measure light intensity at each point

  4. Observe how number of organisms changes with distance from tree
• Quadrats

  • Come in a range of different sizes
  • Used to sample a small area of the habitat
• Random sampling

  Using random numbers to determine quadrat placement
• Total population size

  Calculated as: (Total area / Area sampled) x Number of organisms counted in sample
• Increasing the number of quadrat samples can improve the estimate of total population size
• Factors other than light intensity (e.g. water, minerals) may also affect the distribution of organisms
• This is a required practical for the GCSE syllabus