The principles of Half-Earth are informed by biologist E.O. Wilson and ecologist Robert MacArthur’s theory of island biogeography, which builds on the first principles of population ecology and genetics to explain how distance and area combine to regulate the balance between immigration and extinction in island populations. The theory puts forth that a change in habitat area results in a change in the sustainable number of species by approximately the 4th root. As reserves grow in size, the diversity of life surviving within them also grows; as reserve area is reduced, the diversity within declines swiftly and to a mathematically predictable degree, often immediately and, for some endemic species, forever.

When 90 percent of all habitat is removed, the number of species that can persist sustainably declines to about half. Such is the current condition of many of the most species-rich localities around the world. In these places, if 10 percent of the remaining natural habitat were also removed, most or all of the surviving resident species would disappear.

If, on the other hand, we protect sufficient area, in certain places the amount of species protected would be 85 percent or more. With about half of Earth’s area protected, Earth’s biodiversity enters a zone of global protection.

The science of the Half-Earth Project aims to map and monitor biodiversity at a high-enough resolution to aid conservation decision-makers through our products, including the Half-Earth Project Map and the Species Protection Index (SPI) developed by the Map of Life at Yale University. Data sources include UNEP-WCMC, IUCN, and IPBES. The map is powered by the data storage, computational, and mapping capabilities of the Google Cloud Platform, Google Earth Engine, and Esri. Map of Life works in close collaboration with the GEO Biodiversity Observation Network (BON), E.O. Wilson Biodiversity Foundation, and in partnership with Google, Esri, NASA, the National Science Foundation, National Geographic, and other partners.

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