Chapter 02 · Nature, land & waterBiodiversity & Nature
Alpha diversity
Definition
The species diversity (richness and often evenness) found within a local-scale site, habitat or community. Introduced by ecologist Robert Whittaker in 1972, alpha diversity is the first of three complementary scales: alpha (within sites), beta (turnover between sites) and gamma (total diversity across a landscape).
References
Whittaker (1972) definition; richness vs evenness; Shannon index; sampling effects and rarefaction.
Overview
What it means
Alpha diversity can be measured as a simple species count (richness, S) or with indices that also weight relative abundance, such as Shannon's index, which rises when individuals are spread more evenly among species. Because raw counts depend on sampling effort and area, ecologists use techniques like rarefaction to compare sites fairly.
How it is used
Field ecologists, conservation planners and environmental assessors use alpha diversity to characterise communities and detect change — for example tracking species loss after disturbance or comparing habitats. It underpins biodiversity monitoring, impact assessment and many corporate nature-disclosure metrics.
Why it matters
Biodiversity loss is often measured first at the local scale: falling alpha diversity signals degraded ecosystems, while maintaining it is a common restoration target. Understanding the alpha/beta/gamma distinction prevents misreading landscape-level diversity from site-level data.