How is biodiversity loss measured within a species, ecosystem, or region?

Measuring biodiversity loss involves assessing changes across different biological scales, from genetic variation within a species to the variety of species and ecosystems within a region.1

Measuring Genetic Diversity

Within a species, biodiversity is measured by quantifying genetic variation. Scientists estimate this by sampling genes to determine the proportion of individuals that are heterozygotes at specific gene loci. High levels of genetic variation provide populations with the potential to adapt to environmental changes, while losses in this variation—often caused by overexploitation or habitat destruction—make species more vulnerable to extinction.23

Measuring Species Diversity

At the species level, biodiversity is commonly measured using species richness, which is the total count of unique species in a given area. Because richness does not account for population sizes, ecologists also consider species abundance and the evenness of distribution among species.45

To assess extinction risk, the IUCN Red List of Threatened Species provides a standardized framework. It evaluates species based on five quantitative criteria, including:
* Rates of population decline63
* Geographic range size63
* Current population size63
* Probability of extinction63

Measuring Ecosystem and Regional Diversity

At larger scales, biodiversity is measured by the variety of ecological communities, such as biomes or ecoregions. Ecologists use different spatial scales to track these changes:1
* Alpha diversity: Species richness within a local habitat.4
* Beta diversity: The rate at which species composition changes between habitats.4
* Gamma diversity: The total species richness across a large geographic region.4

By monitoring these metrics, scientists can track the impact of human activities—such as habitat loss, pollution, and climate change—on the stability of life on Earth.631