About the Biodiversity Intactness Index

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How the Biodiversity Trends Explorer works:

• About the Biodiversity Intactness Index
• Assumptions and limitations
• Calculating uncertainty
• External data sets
• Using the Biodiversity Intactness Index in policy

About the Biodiversity Intactness Index

The Biodiversity Intactness Index (BII) summarises the change in ecological communities in response to human pressures. The BII is an estimated percentage of the original number of species that remain and their abundance in any given area, despite human impacts.

The BII is averaged across areas (countries, regions or global) to give the remaining biodiversity across that area.  

The PREDICTS (Projecting Responses of Ecological Diversity In Changing Terrestrial Systems) project calculates the BII using data from ecological studies conducted around the world. This data includes more than 54,000 species, encompassing not only birds and mammals, the groups most often used in biodiversity indicators, but also plants, fungi and insects. 

These studies have allowed us to infer a baseline of the number and diversity of species at near-undisturbed sites, and then to compare this baseline with biodiversity at sites with high human activity.

While each of these studies looked at different species groups in different areas using different sampling methods, we account for this variation in our statistical analysis.

The BII is derived from combining two models. The first model represents how human activity has influenced the total abundance of species in any one area. The second model analyses how similar each site's ecological community is to the near-undisturbed sites (this is known as the compositional similarity and includes what original species are present and what species are dominant).

Next, we combine each of these models with maps of human pressures, including land use change and intensification, human population growth and landscape simplification. This produces new maps of how abundance and compositional similarity have been affected by human pressures. Bringing these two maps together then gives us the BII: the percentage of the original ecological community that remains across an area. 

Assuming that the relationship between biodiversity and human activity does not change, stacking the human driver data from multiple years allows biodiversity projections to be made through history and into the future. 

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Assumptions and limitations