ECOLOGY RP9: sampling organisms

• 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. Calculate total population size using formula
• Using sampling techniques to investigate effect of a factor on species distribution

  1. Place transect line from tree outwards

  2. Use quadrats to count organisms at intervals along transect

  3. Measure light intensity at each quadrat

  4. Analyse relationship between light intensity and organism count
• Quadrats


  • Come in a range of different sizes
  • Used to sample a known area
• Random sampling


  Using random numbers to determine quadrat placement
• Estimating total population size = (Total area / Area sampled) x Number of organisms counted
• Increasing number of quadrats improves accuracy of population estimate
• Transect line used to investigate effect of abiotic factor on species distribution
• Light intensity measured using light meter or app
• As distance from tree increases

  Light intensity increases
• Other abiotic factors like water and minerals may also affect species distribution