IB Environmental Systems and Societies/Measuring biotic components of the system

2.3 Measuring biotic components of the systemEdit

2.3.1 Construct simple keys and use published keys for the identification of organisms.

  • Dichotomous Keys

2.3.2 Describe and evaluate methods for estimating abundance of organisms.

2.3.3 Describe and evaluate methods for estimating the biomass of trophic levels in a community.

2.3.4 Define the term diversity.

  • Diversity is often considered as a function of two components: the number of different species and the relative numbers of individuals of each species.

2.3.5 Apply Simpson’s diversity index and outline its significance.

  • Formula: D = N(N − 1)/ ∑ n(n − 1)


  • D = diversity index
  • N = total number of organisms of all species found
  • n = number of individuals of a particular species
  • D is a measure of species richness. A high value of D suggests a stable and ancient site, and a low value of D could suggest pollution, recent colonization or agricultural management. The index is normally used in studies of vegetation but can also be applied to comparisons of animal(or even all species) diversity.
Last modified on 17 February 2012, at 22:39