There are 25-36+ areas that have been labeled as “Biodiversity Hotspots” because of the variety of organisms, rareness of species, and the threat to their existence. Many are shown on the Myers 2000 edition of hotspot-map.
See also: Science Mag Biodiversity Hotspots
The Biodiversity Index is commonly used to calculate the variety of organisms in a given area using a series of tables and charts to categorize each one. Here are some tools