by Rowan B. Martin

About the author: Rowan B. Martin is an environmental consultant in Zimbabwe, Africa, and a former official with the Zimbabwe Department of National Parks and Wildlife Management.

In most popular accounts, the measure of biological diversity is based on species numbers; therefore, rates of extinction and the listing of endangered species are treated as measures of the trends in biological diversity. . . . The actual number of species that are properly named and recorded is uncertain, and there is no single database that lists them all. . . .

Of the total numbers of species on the globe, the mammals make up about 0.2 percent and the birds about 0.5 percent. However, of all taxonomic groups, the mammals display the greatest diversity, ranging from the pygmy shrew with a body weight of 1.5 grams...