This number, while it may be of some interest to nonscientists, isn’t of much real value to researchers. They are generally more concerned with local biodiversity. Despite the apparent enormity of the number of species that inhabit the earth as a whole, local biodiversity - the number of species found in any one habitat - fluctuates greatly as we cross the boundaries separating the ecosystems that make up the Earth’s biosphere. It reaches its highest levels on the coral reefs and in the tropical rain forests where there may be thousands of species per acre.