How to Calculate Beta Diversity

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Beta Diversity Calculator

Compare species composition and diversity between two ecological sites.

Gamma Diversity (Total Species): 0
Average Alpha Diversity: 0
Whittaker's Beta Diversity (βw): 0
Sorensen Similarity Index: 0
Jaccard Similarity Index: 0

What is Beta Diversity?

Beta diversity is a fundamental concept in ecology that measures the variation in species composition between different locations or along environmental gradients. While Alpha diversity refers to the diversity within a specific site, and Gamma diversity refers to the total diversity of an entire landscape, Beta diversity quantifies the "turnover" or difference between sites.

How to Calculate Beta Diversity

There are several ways to calculate beta diversity. This calculator uses Whittaker's formula, which is one of the most widely accepted methods for simple pairwise comparisons.

The Formulas Used:

  • Gamma Diversity (γ): The total number of unique species found across both sites. Calculated as: S1 + S2 - Shared Species.
  • Average Alpha Diversity (α): The mean number of species per site. Calculated as: (S1 + S2) / 2.
  • Whittaker's Beta (βw): Defined as γ / α. It represents how many times richer the regional landscape is than the average local site.
  • Sorensen Index: A measure of similarity from 0 to 1. Calculated as: (2 * Shared) / (S1 + S2).
  • Jaccard Index: Another similarity measure. Calculated as: Shared / (S1 + S2 - Shared).

Example Calculation

Imagine you are surveying two forest plots:

  • Plot A: 10 species of trees.
  • Plot B: 12 species of trees.
  • Shared: 4 species are found in both plots.

First, find Gamma diversity: 10 + 12 – 4 = 18. Next, find Average Alpha: (10 + 12) / 2 = 11. Finally, Whittaker's Beta Diversity is 18 / 11 = 1.636. This indicates a moderate degree of species turnover between the two plots.

Why Does Beta Diversity Matter?

Understanding beta diversity helps conservationists identify unique habitats. If beta diversity is high, it means different sites harbor very different species, implying that multiple protected areas are needed to conserve the region's total biodiversity. If beta diversity is low, many sites share the same species, and a single large reserve might be sufficient.

function calculateBetaDiversity() { var s1 = parseFloat(document.getElementById("speciesSiteA").value); var s2 = parseFloat(document.getElementById("speciesSiteB").value); var sc = parseFloat(document.getElementById("sharedSpecies").value); var errorDiv = document.getElementById("betaError"); var resultDiv = document.getElementById("betaResult"); // Reset displays errorDiv.style.display = "none"; resultDiv.style.display = "none"; // Validation if (isNaN(s1) || isNaN(s2) || isNaN(sc)) { errorDiv.innerHTML = "Please enter valid numbers for all fields."; errorDiv.style.display = "block"; return; } if (sc > s1 || sc > s2) { errorDiv.innerHTML = "Shared species cannot be greater than the total species in either site."; errorDiv.style.display = "block"; return; } if (s1 === 0 && s2 === 0) { errorDiv.innerHTML = "Species counts cannot both be zero."; errorDiv.style.display = "block"; return; } // Calculations var gamma = s1 + s2 – sc; var alphaAvg = (s1 + s2) / 2; var whittakerBeta = gamma / alphaAvg; var sorensen = (2 * sc) / (s1 + s2); var jaccard = sc / (s1 + s2 – sc); // Display Results document.getElementById("resGamma").innerHTML = gamma; document.getElementById("resAlpha").innerHTML = alphaAvg.toFixed(2); document.getElementById("resWhittaker").innerHTML = whittakerBeta.toFixed(3); document.getElementById("resSorensen").innerHTML = sorensen.toFixed(3); document.getElementById("resJaccard").innerHTML = jaccard.toFixed(3); resultDiv.style.display = "block"; }

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