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The Whittaker Beta Diversity Calculator computes the original beta diversity index proposed by Robert Whittaker in 1960. Whittaker's beta (betaW) measures the extent of species turnover among sites by comparing the total regional diversity (gamma) to the average local diversity (alpha). It is the foundational measure of beta diversity.
This calculator provides both the subtractive form (betaW = gamma/alpha - 1) and the multiplicative ratio (gamma/alpha). Values range from 0 (all sites identical) to N-1 (where N is the number of sites, when sites share no species).
Whittaker's beta diversity is calculated as:
βW = (γ / α) - 1
Where:
When all sites are identical, gamma equals alpha, so betaW = 0. When sites share no species, gamma equals alpha times the number of sites, and betaW approaches N-1. The multiplicative beta (gamma/alpha) represents how many times richer the region is than the average site.
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BetaW = 2.0 means the region is 3 times richer than the average site, indicating substantial species turnover.
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BetaW near 0 means most species are shared across all sites. The landscape is relatively homogeneous.
Robert Harding Whittaker proposed this measure in 1960 in his landmark paper on vegetation of the Siskiyou Mountains. He defined beta diversity as the extent of change in community composition along environmental gradients, formalized as gamma/alpha - 1.
The maximum value is N - 1, where N is the number of sites. This occurs when no species is shared between any pair of sites. For example, with 5 sites where each has 10 unique species and no overlap, gamma = 50, alpha = 10, and betaW = 4.
Both use the same formula (gamma/alpha - 1), but this calculator emphasizes the original Whittaker formulation and provides the multiplicative form. The conceptual approach is identical. Different ecologists may prefer different terminology, but the mathematics are the same.
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