Shannon Diversity Index: Definition & Example


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:

Shannon Diversity Index example

The Shannon Diversity Index for this community is 1.49.

She can also use the following formula to calculate the Shannon Equitability Index:

EH = H / ln(S)

For this example, there are S = 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.

15 Replies to “Shannon Diversity Index: Definition & Example”

  1. thank you for your useful explanation, kindly at the end how can i interpret the obtained Shannon index?

    1. Hi Omran…The Shannon index, also known as Shannon entropy or Shannon-Wiener index, is a measure of biodiversity or uncertainty in a system. In the context of ecology, it is commonly used to quantify the diversity of species within a community. However, the Shannon index can also be applied in other fields to measure the diversity or uncertainty of any categorical variable.

      Here’s how you can interpret the Shannon index:

      1. **Interpretation of the Value:**
      – The Shannon index ranges from 0 to infinity, where:
      – A value of 0 indicates no diversity (i.e., all elements in the system belong to the same category).
      – Higher values indicate greater diversity or uncertainty in the system.
      – For example, in an ecological context, a higher Shannon index suggests a more diverse community with a greater variety of species.

      2. **Comparison Between Groups or Time Periods:**
      – You can compare Shannon index values between different groups or time periods to assess differences in diversity or uncertainty.
      – For example, if you’re studying biodiversity in different habitats, you can compare the Shannon index values to determine which habitat has greater species diversity.

      3. **Relationship with Evenness:**
      – The Shannon index incorporates both species richness (the number of different species) and species evenness (the relative abundance of each species).
      – Higher Shannon index values may indicate not only a greater number of species but also a more even distribution of individuals among those species.

      4. **Consideration of Baseline Values:**
      – It’s essential to consider the baseline or expected value of the Shannon index for your system.
      – For example, if you’re comparing the diversity of plant species in two regions, you might expect higher Shannon index values in regions with more favorable environmental conditions for plant growth.

      5. **Contextual Interpretation:**
      – The interpretation of the Shannon index should always be considered in the context of your specific study or application.
      – It’s important to understand the underlying factors driving diversity or uncertainty in your system and how they relate to the Shannon index values.

      In summary, the Shannon index provides a quantitative measure of diversity or uncertainty, with higher values indicating greater diversity. Interpretation should consider the context of the study, comparisons between groups, and the relationship with other ecological or categorical variables.

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