By Aaron Koenigsberg – Updated August 30, 2022
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Beta diversity quantifies the species turnover between two habitats. It tells us how many species are unique to each environment and how similar the two communities are.
Values can be expressed as a raw count (the number of non‑shared species) or as a normalised index between 0 and 1. A higher value indicates greater dissimilarity.
• S1 – Total species count in habitat 1.
• S2 – Total species count in habitat 2.
• c – Species common to both habitats.
β = (S1 – c) + (S2 – c)
Subtract the shared species from each habitat and add the two differences. The result is the number of species that appear in only one of the two habitats.
Consider two sites with a combined 12 species: A–L.
• Habitat 1 contains 10 species: A–J.
• Habitat 2 contains 7 species: F–L.
• They share five species (F–J).
β = (10 – 5) + (7 – 5) = 7.
Thus, seven species are exclusive to one of the sites.
The index scales the raw value to a 0–1 range, facilitating comparisons across studies.
β' = 2c / (S1 + S2)
Using the same data: c = 5, S1 + S2 = 17.
β' = (2 × 5) / 17 ≈ 0.59.
A value of 0.59 indicates moderate dissimilarity between the two habitats.
These calculations are standard in community ecology and are widely used in biodiversity monitoring, conservation planning, and ecological research.
