Random Sampling (Cambridge (CIE) A Level Biology): Revision Note

Random sampling

• Measuring the different levels of biodiversity within an ecosystem can be a time-consuming task

• Finding out which species live in an ecosystem and the size of the populations requires the identification and cataloging 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

• However, for larger and more complex ecosystems like rainforests, it is simply impossible to find, identify and count every organism that exists there

• When this is the case different samples of the area can be taken and used to make estimates of the total species numbers in the area

Sampling

• Sampling is a method of investigating the abundance and distribution of species and populations

• There are two different types of sampling:

  • Random

  • Systematic

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

  • This method is beneficial because it means there will be no bias on the part of the person that is carrying out the sampling that may affect the results

• In systematic sampling the positions of the sampling points are chosen by the person carrying out the sampling

  • There is a possibility that the person choosing could show bias towards or against certain areas

  • Individuals may deliberately place the quadrats in areas with the fewest species as these will be easier and quicker to count

  • This is unrepresentative of the whole area

• 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