18.2.2—Levels of biodiversity assessment

Biodiversity describes the range and variety of genes, species and habitats within a region. It can be assessed at three linked levels.

• Ecosystem/habitat diversity — the number and range of different ecosystems or habitats in the area.
• Species diversity — the number of different species and how evenly individuals are distributed among them.
• Genetic diversity — the variety of genes and alleles within each species, including differences between populations of the same species.

Species richness is only the number of species. Species diversity also considers evenness: an area can contain many species but still have lower species diversity if most individuals belong to one or two species. Keep these terms separate when interpreting evidence.

Biodiversity can support ecosystem resilience because variation provides more ways for populations and ecosystems to respond to environmental change. This is a general ecological relationship, not a guarantee that every diverse ecosystem resists every disturbance.

Biodiversity is broader than a species count: ecosystem/habitat, species and genetic levels answer different questions. This card defines the assessment levels; random sampling, field methods, correlation tests and Simpson’s index are separate cards.