Beta Diversity Calculators

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Beta diversity measures the variation in species composition between different sites, habitats, or communities — the degree to which communities differ from one another. While alpha diversity describes diversity within a site and gamma diversity describes total diversity across a landscape, beta diversity links them: gamma = alpha × beta (in Whittaker's multiplicative framework). Beta diversity reflects species turnover along environmental gradients, habitat fragmentation, and metacommunity dynamics. It is quantified using indices including Whittaker's β, Jaccard similarity, Sørensen index, and Bray-Curtis dissimilarity.

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Whittaker's Beta Diversity

β_W = γ / ᾱ − 1

γ = total species richness across all sites; ᾱ = mean alpha diversity per site. Example: 3 sites with 10, 12, and 8 species (ᾱ = 10); total species pool γ = 20. β_W = 20/10 − 1 = 1.0. β = 0 means all sites are identical; higher values mean greater turnover.

Pairwise Beta Diversity Indices

  • Jaccard dissimilarity: β_J = (b + c) / (a + b + c). a = shared species, b = unique to site 1, c = unique to site 2. Range 0–1.
  • Sørensen dissimilarity: β_S = (b + c) / (2a + b + c) — weights shared species more heavily.
  • Bray-Curtis: Uses abundance data, not just presence/absence; preferred when counts or cover data are available.

Turnover vs. Nestedness

Total beta diversity can be partitioned into: Turnover — species at one site replace species at another (true compositional change along gradients); Nestedness — poorer sites are subsets of richer sites (e.g., after habitat fragmentation). The Baselga framework (betapart R package) separates these components, revealing mechanisms driving beta diversity patterns.

Glossary

Beta Diversity
Variation in species composition between sites; Whittaker's β = γ/ᾱ − 1; high beta diversity means high species turnover or community differentiation between locations.
Jaccard Dissimilarity
Pairwise beta diversity for presence/absence: (b+c)/(a+b+c); ranges 0 (identical) to 1 (no shared species); a = shared species, b and c = species unique to each site.
Bray-Curtis Dissimilarity
Abundance-based pairwise beta diversity index (0–1); preferred over Jaccard when species count or cover data are available; widely used in ecological ordination.

Frequently Asked Questions

Beta diversity measures species composition change between sites. Whittaker's formula: β = γ/ᾱ − 1 (total species / mean site species − 1). Pairwise: Jaccard dissimilarity = (b+c)/(a+b+c) for presence/absence; Bray-Curtis for abundance data (both range 0 = identical to 1 = no shared species). High beta diversity means communities differ greatly in composition; low beta diversity means sites share most species.

Alpha diversity: species richness within one site. Gamma diversity: total richness across all sites in the landscape. Beta diversity: the variation between sites — mathematically, γ = ᾱ × (β + 1) in Whittaker's multiplicative framework. High gamma diversity can result from high alpha (each site is rich) or high beta (sites differ greatly in composition). Understanding which driver dominates has different conservation implications for habitat management strategies.

Turnover: species at one site are genuinely replaced by different species at another — true compositional change along environmental gradients. Nestedness: the species at species-poor sites form a subset of those at richer sites — not different species, just fewer. Nestedness typically results from selective extinction after habitat fragmentation or from colonization filters. The Baselga (2010) framework partitions total beta diversity into these two components using the betapart R package, revealing ecological mechanisms.

Jaccard uses presence/absence only — which species are there, not how many. It is appropriate when abundance data are unavailable or unreliable. Bray-Curtis incorporates species abundances — communities with the same species but very different abundances are considered dissimilar. Use Bray-Curtis when you have reliable count or cover data and abundance differences are ecologically meaningful. Bray-Curtis is generally preferred for NMDS ordination, PERMANOVA testing, and gradient analysis in community ecology.