Simpson’s Diversity for OCR and Edexcel

Various methods have been devised for quantifying the diversity of a plant and animal community (Diversity Indices). All of them are based on the relationship between the total number of individuals present and the number of individuals per species. One of the simplest is the Simpson Diversity Index.

D = 1 – (Σ(n/N)²)

Where:

D = diversity index
n = Number of individuals of each species
N = Total number of individual plants or animals
Σ = sum

The procedure involves noting every plant or animal in the area under investigation.

Example:

An area of soil which had been recently cleared of vegetation was studied after one year’s colonisation, and the following plants were found in an area 5m².

Species Number
Daisy (Bellis perennis) 15
Scentless mayweed (Matricaria perforata) 10
Groundel (Senecio vulgaris) 104
Ragwort (Senecio jacobaea) 42
Hairy bittercress (Cardamine hirsuta) 55
Fat hen (Chenopodium album) 22
Nettle (Urtica dioica) 9
Forget-me-not (Myosotis arvensis) 7
Field speedwell (Veronica persica) 17
Total: 281

D = 1 – ((15/281²) + (10/281²) etc.)
= 1 – 0.2126
= 0.79

On visiting the area a year later, the diversity index was found to have dropped to 0.54, suggesting the community was in a phase of instability.

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