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.

Lorsque 90 % de l'habitat est supprimé, le nombre d'espèces pouvant persister durablement diminue de moitié environ. Telle est la situation actuelle de nombreuses localités parmi les plus riches en espèces dans le monde. Dans ces endroits, si 10 % de l'habitat naturel restant était également supprimé, la plupart ou la totalité des espèces résidentes survivantes disparaîtraient.

En revanche, si nous protégeons une superficie suffisante, dans certains endroits, le nombre d'espèces protégées serait de 85 % ou plus. Avec environ la moitié de la surface de la Terre protégée, la biodiversité de la Terre entre dans une zone de protection globale.

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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