The Shannon Diversity Index (sometimes called the Shannon-Wiener Index) is a way to measure the diversity of species in a community.
Denoted as H, this index is calculated as:
H = -Σpi * ln(pi)
where:
- Σ: A Greek symbol that means “sum”
- ln: Natural log
- pi: The proportion of the entire community made up of species i
The higher the value of H, the higher the diversity of species in a particular community. The lower the value of H, the lower the diversity. A value of H = 0 indicates a community that only has one species.
The Shannon Equitability Index is a way to measure the evenness of species in a community. The term “evenness” simply refers to how similar the abundances of different species are in the community.
Denoted as EH, this index is calculated as:
EH = H / ln(S)
where:
- H: The Shannon Diversity Index
- S: The total number of unique species
This value ranges from 0 to 1 where 1 indicates complete evenness.
The following step-by-step example shows how to calculate the Shannon Diversity Index and the Shannon Equitability Index for a given community.
Step 1: Collect the Data
Suppose a biologist wants to measure the diversity of species in a local forest. She collects the following data:
Step 2: Calculate the Proportions
Next, the biologist can calculate the proportion of the community made up of each species.
For example, there are a total of 105 individuals and 40 are classified as species A. Thus, species A makes up 40 /105 = 0.38 of the total community.
She can perform a similar calculation for each species:
Step 3: Calculate the Natural Log of the Proportions
Next, she can calculate the natural log of each proportion:
Step 4: Multiply the Proportions by the Natural Log of the Proportions
Next, she can multiply the proportions by the natural log of the proportions:
Step 5: Calculate the Shannon Diversity Index
Lastly, she can use the following formula to calculate the Shannon Diversity Index:
H = -Σpi * ln(pi)
For this example, she can take the sum of the last column and multiply by negative one:
The Shannon Diversity Index for this community is1.49.
She can also use the following formula to calculate the Shannon Equitability Index:
EH = H / ln(S)
For this example, there areS = 5 total species, so see can calculate this index to be:
EH = 1.49 / ln(5) =0.92.
Additional Resources
Feel free to use this Shannon Diversity Index Calculator to automatically calculate the Shannon Diversity Index for any dataset.
