Biodiversity Index Biology • PCM Notes
H' = −Σ (pi × ln pi)

Shannon-Wiener Index measures species diversity. Higher H' = greater diversity.

Enter Number of Individuals per Species

Understanding Biodiversity Indices

Quick Answer: The Shannon-Wiener Index (H') quantifies species diversity in a community, accounting for both richness (number of species) and evenness (relative abundance). H' = 0 means no diversity (single species).

Key Formulas

Shannon-Wiener: H' = -Σ pi ln(pi) where pi = proportion of individuals belonging to species i. Evenness: J' = H' / ln(S). Simpson Index: D = 1 - Σ pi2. Higher values of all three indicate greater diversity.

Solved Examples

Community A (equal)
Sp1=25, Sp2=25, Sp3=25, Sp4=25
H' = 1.39, J' = 1.0
Maximum evenness
Community B (unequal)
Sp1=70, Sp2=10, Sp3=10, Sp4=10
H' = 0.94, J' = 0.68
Lower evenness
Monoculture
Sp1=100
H' = 0.0
No diversity

FAQs

What is the difference between species richness and evenness?

Species richness is the count of different species. Evenness measures how equal the abundances are. High diversity requires both many species and relatively equal abundance.

Why use natural log (ln) in Shannon index?

Using natural log is standard in ecology. Some use log base 2 or log base 10, but ln is most common. Values are comparable as long as the same base is used.

What does a Shannon index value of 1.5 mean?

A value of 1.5 indicates moderate diversity. Typical values range from 0 (no diversity) to around 4.5 (very high diversity in tropical ecosystems).