2.5

• • Biotic factors - e.g. abundance of organisms (density, percentage cover or frequency), identification of species, biomass, species richness and diversity.
  • Abiotic factors - e.g. temperature, salinity or wind speed. 
• Random sampling - least biased sampling
• systematic sampling - nth method
• Stratified sampling

  This technique is used when the population is known to contain subsets. It is important to know the size of the subsets in the whole population so that your sample reflects the same proportions.
• Motile animals are ones that are mobile. There is a wide range of ways to estimate the abundance of motile animals. Methods may involve direct counting and sampling or indirect techniques such as the Lincoln index covered in the next section. Either way there may have to be some method to capture the animals, at least temporarily for the count.
• The Lincoln Index is an indirect method by which the size of an animal population can be estimated. It is also called the capture/mark/release/recapture method – which gives you some hint as to how it works.
• Lincoln index:

  N = n1 × n2 / m2

  Where:

  N = total population.

  n1 = number of animals marked in the first capture and released.

  n2 = number of animals recaptured (second sample).

  m2 = number of animals marked in the recapture (second sample).
• simpson's diversity index: a measure of the diversity of a community