Chapter 02 · Nature, land & waterBiodiversity & Nature
Beta diversity
Definition
The variation in species composition among sites within a region — the extent to which different habitats host different species. In Robert Whittaker's 1972 framework, beta diversity multiplicatively links alpha diversity (within-site richness) and gamma diversity (total regional diversity): gamma ≈ alpha × beta. High beta diversity means sites are compositionally distinct; low beta diversity means the same species recur everywhere (biotic homogenisation).
References
Whittaker's alpha/beta/gamma framework; beta as turnover between sites; measurement approaches.
Overview
What it means
Beta diversity captures something alpha diversity cannot: whether a landscape is a mosaic of distinct communities or a uniform blur. Two regions with identical average alpha diversity can differ hugely in conservation value if one has high turnover (many unique local communities) and the other has been homogenised by disturbance and invasive generalists.
How it is used
Ecologists measure beta diversity with dissimilarity indices (for example Jaccard or Bray–Curtis) to assess fragmentation effects, design protected-area networks (protecting complementary sites, not just the richest ones), and track biotic homogenisation under global change. It informs landscape-level conservation planning and restoration targets.
Why it matters
Conservation that protects only local richness can still lose regional diversity if all sites converge on the same species. Beta diversity is the scale at which landscape structure and connectivity — core to 30×30 planning — are measured.