Beta Diversity Calculator

Calculate alpha, beta, gamma diversity and partition beta into nestedness and turnover components.

Species only in community A (a) (species)

Species only in community B (b) (species)

Shared species (c) (species)

Please check your inputs and try again.

Three Scales of Diversity

Diversity is measured at three nested scales, and beta diversity is the link between them.

Scale	Symbol	What it counts
Alpha	α	Diversity within one site
Beta	β	Turnover between sites
Gamma	γ	Total diversity across the whole region

The relationship γ = α × β means high regional diversity can arise two ways: each site being individually rich, or sites differing strongly from one another. These have opposite conservation implications — high beta diversity means protecting one site captures little of the region's biodiversity.

Sørensen or Jaccard?

Sørensen = 2c/(2c + a + b) Jaccard = c/(a + b + c)

Index	Weighting	Use when
Sørensen	Double weight on shared species	Shared occurrence is more meaningful than absence
Jaccard	Equal weight	More conservative; standard in many ecological studies

Sørensen always gives a higher similarity value than Jaccard for the same data, because it counts shared species twice. Comparing a Sørensen value from one study with a Jaccard value from another is a common error — always state which index was used.

Turnover Versus Nestedness

Two communities can be equally dissimilar for completely different reasons. Turnover means species replace one another between sites. Nestedness means one site holds a subset of the other's species. Distinguishing them matters: nestedness suggests protecting the richest site suffices, while turnover requires a network of reserves.

Worked Examples

Example 1: Nearby forest fragments: a=10, b=12, c=8

Sorensen=2x8/38=0.42

Result: Moderate similarity, mostly turnover

Different microhabitat species

Example 2: Adjacent habitats: a=2, b=3, c=15

Sorensen=2x15/35=0.857

Result: High similarity, mostly nested

Richer community contains poorer one

Example 3: Turnover versus nestedness

Site A has 18 species, site B has 20, sharing 8

Result: Turnover-dominated

Ten species occur only in A and twelve only in B — neither is a subset of the other. Protecting both sites is necessary to capture regional diversity.

Example 4: Nested pattern

Site A has 5 species, site B has 20, sharing all 5

Result: Nestedness, not turnover

A is a strict subset of B. Protecting B alone captures everything, which is a very different conservation conclusion from the turnover case.

Common Mistakes

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Comparing Sørensen and Jaccard values directly

Sørensen weights shared species double and always returns a higher similarity. Values from the two indices are not interchangeable.

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Ignoring sampling effort

Unequal sampling inflates apparent turnover, because rare species are missed at the less-sampled site. Rarefaction or equal effort is essential.

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Treating all beta diversity as turnover

High dissimilarity can arise from nestedness instead, where one community is a subset of the other. The conservation response differs entirely.

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Using presence-absence when abundance matters

Sørensen and Jaccard ignore how common each species is. Bray–Curtis or Morisita–Horn incorporate abundance where that is relevant.

Frequently Asked Questions

Alpha beta gamma?

Alpha: local (per site). Beta: between-site diversity. Gamma: regional pool. Gamma = alpha x beta (multiplicative framework).

Conservation use?

Nestedness→protect largest habitats. Turnover→protect different sites to maximize gamma diversity.

What is the difference between alpha, beta and gamma diversity?

Alpha is diversity within a site, gamma is total regional diversity, and beta measures turnover between sites. They relate as gamma = alpha × beta.

Should I use Sørensen or Jaccard?

Jaccard is more conservative and weights presences equally. Sørensen doubles the weight on shared species and gives higher similarity values. State which you used.

What is the difference between turnover and nestedness?

Turnover means species replace each other between sites; nestedness means one site's species are a subset of another's. Turnover requires a reserve network, nestedness does not.

Why does high beta diversity matter for conservation?

Because it means sites differ substantially. Protecting a single reserve captures only a small fraction of regional biodiversity when turnover is high.