Shannon Diversity Index Calculator
Calculate Shannon diversity index H and evenness J from species abundance data. Higher H indicates greater biodiversity. Compare communities and assess species richness and evenness.
🌳 Ecology📐 H = -Σ(pi · ln(pi))🧬 Biology
Species 1 abundance n1
Species 2 abundance n2
Species 3 abundance n3
Species 4 abundance n4 (optional)
Species 5 (optional)
Species 6 (optional)
Please enter valid values.
Formula & Reference
| Variable | Symbol | Formula | Units |
|---|---|---|---|
| Shannon Diversity Index Calculator | — | H = -Σ(pi · ln(pi)) | nats or bits |
Step-by-Step Examples
Example 1
Forest community
4 tree species: 60, 30, 8, 2 individuals.
- N=100, pi = 0.60, 0.30, 0.08, 0.02
- H = -(0.60ln0.60+0.30ln0.30+0.08ln0.08+0.02ln0.02)
- = -(−0.306−0.361−0.180−0.078) = 0.925
- J = 0.925/ln(4) = 0.925/1.386 = 0.668
✓ H = 0.925 nats, J = 0.668 (moderate evenness)
Example 2
Equal abundance
4 species, 25 each: maximum diversity.
- Each pi = 0.25
- H = -4×(0.25×ln0.25) = -4×(-0.347) = 1.386
- J = 1.386/1.386 = 1.0 (perfect evenness)
✓ H = 1.386 = H_max; J = 1.0
Example 3
Dominance community
Species 1 has 95 of 100 individuals.
- p1=0.95: -0.95×ln(0.95)=0.049
- p2=p3=p4=0.0167: each -0.0167×ln(0.0167)=0.069
- H ≈ 0.049+3×0.069 = 0.256
- Low H: one species dominates
✓ H = 0.256 (low diversity, one dominant species)
Real-World Applications
Conservation Biology
Higher H indicates healthier, more resilient ecosystem. Monitoring H tracks habitat degradation.
Environmental Science
Compare biodiversity before and after disturbance (fire, logging, pollution). H quantifies impact.
Aquatic Ecology
Benthic macroinvertebrate H used as water quality indicator. Pollution tolerant species dominate degraded streams.
Microbial Ecology
Gut microbiome diversity measured by Shannon H. Higher H associated with better health outcomes.
Common Mistakes to Avoid
⚠️
Need species counts, not just richness
H accounts for evenness (how equal abundances are) as well as richness (number of species). Two communities with same species can have very different H.
⚠️
H uses natural log by default
Some use log2 (bits) instead of ln (nats). Specify units when reporting H values.
⚠️
J is always 0 to 1
Evenness J = H/H_max. J=1: all species equally abundant. J=0: one species has all individuals (H=0).
Frequently Asked Questions
What is the Shannon diversity index? ▾
H = -Σpi ln(pi). Measures uncertainty: if H is high, you cannot predict which species you will encounter. Combines species richness and evenness.
What is evenness and why does it matter? ▾
Two forests: A has 100 species each with 1 individual; B has 100 species with one having 99% of all individuals. Same richness, very different H and J. Evenness captures dominance.
What is Simpson's diversity index? ▾
D = Σpi². Probability two randomly selected individuals are the same species. 1-D = probability they differ. Less sensitive to rare species than Shannon H.
How does H compare to species richness? ▾
Adding rare species increases richness (S) more than H. H is weighted by abundance: rare species contribute little. H and S often correlated but not identical.
What H values indicate healthy ecosystems? ▾
Varies by ecosystem type. Temperate forests: H ≈ 2-4. Tropical forests: H > 4. Heavily disturbed: H < 1. Pristine coral reefs: H ≈ 3-5.