Whittaker Beta Diversity Calculators

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Beta diversity (β-diversity) measures the change in species composition between ecological communities — quantifying how different communities are from one another. Whittaker's beta diversity (βW) is the ratio of total species richness across a landscape (gamma diversity) to average species richness within communities (alpha diversity). High β-diversity means communities share few species; low β-diversity means they share most. Beta diversity is a key concept in macroecology, conservation biology, and biogeography.

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Whittaker's Beta Diversity Formula

βW = γ / ᾱ

γ (gamma diversity) = total species in the landscape; ᾱ (alpha diversity) = mean species richness per community. βW ranges from 1 (all communities identical — no turnover) to γ (each community entirely unique — maximum turnover).

Worked Example

Three plots: A = {oak, maple, birch} (3 spp), B = {maple, pine, cedar} (3 spp), C = {birch, walnut, cherry} (3 spp).
Gamma = 7 unique species; mean alpha = 3.
βW = 7/3 = 2.33 — moderate turnover.

Other Beta Diversity Metrics

  • Sørensen dissimilarity: βSOR = 1 − 2c/(a+b) — presence/absence, ranges 0–1
  • Bray-Curtis dissimilarity: Abundance-weighted — widely used in community ecology
  • Additive beta: β = γ − ᾱ (absolute species gain)

Turnover vs. Nestedness

Beta diversity can be decomposed into species replacement (turnover) — different species at different sites — and nestedness — poorer communities are subsets of richer ones. Conservation planning uses this distinction to identify whether sites are genuinely distinct or merely depauperate versions of each other.

Scales and Gradients

Beta diversity typically increases toward the equator — tropical communities are more compositionally distinct from one another than temperate communities at equivalent distances.

Glossary

Beta Diversity (βW)
Whittaker's measure of species turnover between communities: βW = γ/ᾱ. Ranges from 1 (identical communities) to γ (all communities unique). Measures compositional dissimilarity across a landscape.
Gamma Diversity (γ)
Total species richness across all communities in a landscape or region — the regional species pool. Equals alpha × beta (multiplicative) or alpha + beta (additive) depending on the partitioning framework.
Alpha Diversity (α)
Species richness within a single community or sample site. Average alpha (ᾱ) = mean richness across all communities — used as the denominator in Whittaker's beta diversity formula.

Frequently Asked Questions

βW = γ/ᾱ — the ratio of total species richness (gamma diversity) to mean per-community richness (alpha diversity). It measures how different communities are from one another in species composition. βW = 1 means all communities have identical species. Higher βW means more turnover — communities share fewer species. It answers: 'How many communities must I sample to encounter all species in the landscape?'

Alpha (α) = within-community diversity (local richness). Gamma (γ) = total landscape diversity (regional species pool). Beta (β) = between-community diversity. Multiplicative relationship: γ = α × β (Whittaker). Additive: γ = α + β. High beta means high regional diversity relative to local diversity — many unique species at each site. Low beta means most regional species are present at every local site.

βW is a ratio of diversities (ranges 1 to γ) — a multiplicative landscape-level measure. Sørensen dissimilarity = 1 − 2c/(a+b) — ranges 0–1, measuring pairwise compositional dissimilarity between two communities (c = shared species, a and b = richness at each site). Sørensen is more commonly used in pairwise comparisons and multivariate community ecology; βW is more useful for landscape-level assessments across multiple communities.

High beta diversity means different sites support distinct species assemblages — protecting any single site misses most regional biodiversity. Conservation planning must account for beta diversity to ensure the full regional species pool is represented in protected areas. Reserves designed based only on local species richness (alpha diversity) may select redundant areas with similar communities. Beta diversity analysis identifies complementary sites that together maximize total protected biodiversity.