Biodiversity is a contraction of 'biological diversity' and is used to describe the variety of life. It refers to the number and variety of organisms within a particular area, and has three components:
- species diversity
- ecosystem (habitat) diversity
- genetic diversity
Species diversity refers to the number of different species and the numbers of individuals of each species within any one community.
Species richness is the number of different species present in an area. The more species present in a sample the 'richer' the area.
Species richness as a measure on its own takes no account of the number of individuals of each species present. Simpson's index (D) is a measure of diversity that takes into account both species richness and an evenness of abundance among the species present. In essence it measures the probability that two individuals selected randomly from an area will belong to the same species. The formula for calculating D:
The value of D ranges from 0 to 1. With this index, 0 represents infinite diversity and 1, no diversity. The lower the value of D (ie closer to 0), the greater the diversity.
To calculate Simpson's index, the…