C4.1.3-4.1.4 Population

• Random quadrat sampling to estimate population size for sessile organisms


  1. Locate habitat

  2. Designate squared area

  3. Choose random coordinates

  4. Place quadrat and count individuals
• Quadrat


  Wooden square frame placed on surface to count number of a specific species
• Quadrat method is used for terrestrial habitats, grassland, and rocky shores
• Quadrat should be used randomly to get a fair result
• Calculating standard deviation shows variability in data and even distribution of results
• Capture-mark-release-recapture to estimate population size for motile organisms

  1. Capture and mark individuals (M)

  2. Release marked individuals

  3. Capture second sample (N)

  4. Count marked individuals in second sample (R)

  5. Calculate population size using Lincoln index
• Lincoln index


  Number of populations = M x N/R
• Marking of species should be done in such a way that it:


  • Won't affect movement of individual
  • Won't be evident for predators
• Capture-mark-release-recapture technique is not very accurate due to assumptions of no immigration/emigration, no death/birth, and predators eating marked individuals faster