Sampling

• What are the 2 types of variation?

  Interspecific and Intraspecific
• What is interspecific variation?

  Differences BETWEEN species
• What is intraspecific variation?

  Differences WITHIN the same species
• What is random sampling?

  Taking a sample of a population and making conclusions BUT sample may be unrepresentative of population
• What is sampling bias?

  Scientists may choose to take plant samples from an area that is not muddy.
• What is Chance?


  By chance individuals chosen may not be representative.
• Using Quadrats?


  Quadrats are placed to avoid bias.

  Lay out a grid using tapes and then using a random number generator to provide the co-ordinates for positioning the quadrats.
• What is systematic sampling?

  Systematic sampling avoids bias.

  A grid is layed out over a map or plan of the area to be studied and sampling points are located at regular intervals.
• What is systematic sampling(lines)?

  A rope or tape is stretched across the habitat in a straight line to form a transect.

  Quadrats are then sampled at regular intervals along the transect.
• What is a line transect?


  Sample everything that touches the line.

  Only feasible where there aren`t too many organisms.
• What is an interrupted Line transect?

  Sample at intervals (every 1 m)
• What is a belt Transect?

  Quadrats placed in a continuous line along the transect.

  Feasible over short distances.
• What is a Interrupted belt or ladder transect?

  Quadrat placed at intervals (every 1 m)along the transect.

  A good compromise
• What 2 things make valid data?


  Using a large sample size: less probability that chance will influence the result/more reliable.

  Analysis of collected data: use statistical tests to determine the part that chance played.