Pielou’s Evenness (J’)

Understanding Pielou's Evenness Index (J')

Pielou's Evenness Index (J') is a measure of species evenness, which describes how similar the abundances of different species are within a community. It is derived from the Shannon Diversity Index (H').

Formula:

J' = H' / Hmax

• H' is the Shannon Diversity Index, calculated as: H' = - Σ (pi * ln(pi))
  • pi is the proportion of individuals belonging to species i (i.e., n_i / N).
  • ln is the natural logarithm.
• Hmax is the maximum possible Shannon diversity for the observed number of species (S). It is calculated as: Hmax = ln(S)
  • S is the Species Richness (total number of different species present).

Interpretation:

• J' values range from 0 to 1.
• A value of J' close to 1 indicates high evenness, meaning that the species in the community have very similar abundances.
• A value of J' close to 0 indicates low evenness, meaning that one or a few species dominate the community in terms of abundance, while others are rare.
• If S=1 (only one species), H' = 0 and H_max = ln(1) = 0. In this case, J' is typically considered to be 1 (perfect evenness for a single species) or undefined. This calculator will state 1 by convention if S=1 and H'=0. If S=0, all values are typically 0 or undefined.

How to Use:

1. Enter the number of individuals (count) for each species identified in your sample.
2. Use the "Add Species" button to create more input rows as needed.
3. Click "Calculate Evenness" to see Pielou's J' and related diversity metrics.