Testing for Distribution and Abundance

• Measuring all the different levels of biodiversity within an ecosystem could be very time-consuming
• Finding out which species live in an ecosystem and the size of the populations


  Identification and cataloguing of all organisms present to build a species list
• This is possible for areas that are very small or where the species are very large like trees
• For larger and more complex ecosystems like rainforests, it is simply impossible to find, identify and count every organism that exists there
• When it is impossible to find, identify and count every organism

  Different samples of the area can be taken and used to make an estimate for the total species numbers in the area
• Sampling


  A method of investigating the abundance and distribution of species and populations
• Types of sampling


  • Random
  • Systematic
• Random sampling


  The positions of the sampling points are completely random or due to chance
• Systematic sampling


  The positions of the sampling points are chosen by the person carrying out the sampling
• When a sampling area is reasonably uniform or has no clear pattern to the way the species are distributed then random sampling is the best choice
• Sampling methods


  • Quadrats (for non-motile or slow-moving species)
  • Transects (for non-motile or slow-moving species)
  • Mark-release-recapture (for motile species)
• Frame quadrats


  Square frames used to mark off the area being sampled
• Using quadrats to investigate percentage cover of species


  1. Divide quadrat into 100 smaller squares

  2. Count number of squares covered by each species

  3. Calculate percentage cover for each species
• Species frequency


  The probability that the species will be found within any quadrat in the sample area
• Calculating species frequency


  Number of quadrats the species was present in / Total number of quadrats x 100
• Belt transects


  A line represented by a measuring tape, along which samples are taken
• Using belt transects


  1. Place quadrats at regular intervals along the tape

  2. Record the abundance of each species within each quadrat
• Mark-release-recapture


  A method for estimating the number of individuals in a population of motile animals
• Mark-release-recapture method


  1. Take first large sample, mark individuals, release back

  2. Take second large sample, count marked and unmarked individuals

  3. Use formula to calculate population estimate
• Assumptions for mark-release-recapture method
• ACFOR scale


  A method used by biologists to estimate abundance: Abundant, Common, Frequent, Occasional, Rare
• For seabed analysis, the use of quadrats is carried out, using specialist diving equipment and expertise to analyse and identify the contents of the quadrats