Measuring the distance and abundance of organisms

• Distribution

  = Where individual organisms are found within an ecosystem.

  • Organisms are generally found where abiotic and biotic factors favour them, therefore their survival rate is high.
• Measuring distribution 


  A belt or line transect is normally used. They are forms of systematic and non-random sampling.

  • Systematic sampling= different areas within an overall habitat are identified which are then sampled separately. This allows scientists to study how the differing abiotic factors in different areas of the habitat affect the distribution of a species.
• Abundance of organisms 


  = The number of individuals of a species present in an area at any given time.

  • Immigration and births increase the numbers of individuals
  • Emigration and deaths decrease the number of individuals
• Measuring abundance

  Population size is estimated.

  • Use a large sample size
  • Use a random sampling technique
• Measuring plant abundance

  Estimated population size= number of individuals in a sample/ area of sample
• Measuring animal abundance

  1. Capture as many individuals in a sample area
  2. Mark or tag each individual
  3. Release marked individuals back into sample area and allow time for them to redistribute themselves in the habitat
  4. Recapture as many individuals in original sample area
  5. Record number of marked and unmarked individuals present
  6. Estimated population size= (number of individuals in first sample X number of individuals in second sample)/ number of recaptured marked individuals.
• Limitation of capture and recapture

  Doesn't take into account births/ deaths

  Animals don't redistribute evenly

  Sample may not be representative of whole population

  Immigration