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•  Richness and evenness are components of biodiversity

Biodiversity describes the variety and variability of all living organisms within a given ecological area

  • Biodiversity can be used to refer to the number of species, their genetic diversity or habitat variety (ecological variations)

There are two main components that contribute to biodiversity – species richness and species evenness

  • Species richness describes the number of different species present in an area (more species = greater richness)
  • Species evenness describes the relative abundance of the different species in an area (similar abundance = more evenness)

Biodiversity (Richness versus Evenness)


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•  Analysis of the biodiversity of two local communities using Simpson’s reciprocal index of diversity

The Simpson’s reciprocal index can be used to measure the relative biodiversity of a given community

  • It takes into account both the number of species present (richness) and the number of individuals per species (evenness)
  • A higher index value is indicative of a greater degree of biodiversity within the community

Simpson Index

Simpson’s reciprocal index can be used to compare communities to identify intrinsic qualities:

  • A high index value suggests a stable site with many different niches and low competition (high richness and evenness)
  • A low index value suggests a site with few potential niches where only a few species dominate (low richness and evenness)
  • The index value may change in response to an ecological disturbance (such as human intervention or natural disasters)

Practice Question

Use Simpson's reciprocal index to compare the biodiversity at two specific locations:
Site 1: Species A = 6 ; Species B = 1 ; Species C = 1
Site 2: Species A = 4 ; Species D = 4