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

2.3 Measuring biotic components of the system


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.