Biodiversity Step 3 / Species Diversity Worksheet
The Shannon and Simpson indices are the two most widely used species diversity indices for examining overall community characteristics. Both are derived from a function used in the field of information (mainly insurance companies) and have been adapted by ecologists to describe the average degree of uncertainty of predicting the species of an individual picked at random from the community. The uncertainty of occurrence increases both as the number of species increases and as the individuals are distributed more and more evenly among the species already present.
THE SHANNON-WIENER SPECIES DIVERSITY INDEX
The Shannon-Wiener species diversity index, when properly manipulated, will always result in a diversity value (H') ranging between 0 (indicating low community complexity) and 4 (indicating high community complexity). It is not necessary to key all organisms to their specific species nomenclature (i.e. organisms which can not be expediently identified may be assigned numeric values such as species 1, 2, 3, etc.). However, in order to derive accurate diversity values, all organisms should be keyed to the lowest possible like taxonomic level. The following is an example of the Shannon-Wiener formula and how it should be used.
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N = Total # individuals in all species
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Ni = # of individuals in each species
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3.322= Conversion factor from base 10 to base 2
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H' = Diversity (0-4)
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REPLICATE #:
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DATE:
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LOCATION:
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Species
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Ni
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log Ni
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Ni (log Ni)
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Cheatocerus sp.
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15
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1.17
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17.55
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Skeletonema sp.
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20
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1.3
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26.00
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Thallassiomena sp.
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17
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1.23
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20.90
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Cosinodiscus sp.
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19
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1.28
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24.32
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Sagitta sp.
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12
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1.08
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12.96
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N =83
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 Ni (log Ni) = 101.73
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For each replicate, apply the Shannon-Wiener formula separately; then, find the mean (average) H' (species diversity). Then go on to find the standard deviation of that average H' if you choose to. Details for standard deviation are on Biodiversity Step 3 forms. The purpose of replication is to quantify the degree of variability in the sampling scheme.