How Many Species are There?
The number of known species is continually in flux as new species are found, taxonomic categories adjusted, and redundancies recognized. Compounding the problem is the fact that diversity is not evenly distributed across species, regions, or the planet. Seventy percent of the world’s species occur in only 12 countries: Australia, Brazil, China, Columbia, Ecuador, India, Indonesia, Madagascar, Mexico, Peru, and Zaire.
Current estimates of the total number of species on Earth range from 5 to 30 million, of which, the 2005 Millennium Ecosystem Assessment notes approximately 2 million have been formally described. Determining an accurate count is a challenging job because there is no central registry for species. Often species that have been described by scientists in one part of the world are also recorded and described by scientists in another. It takes time and research to recognize these redundancies, though there are several professional partnerships, such as Species 2000, attempting to create a single nomenclature and taxonomic registry.
Some species, such as many large mammal, butterfly, bird, plant, and insect species, have been well studied. Over half of all described species are insects, including nearly 300,000 known beetles. However, the estimated number of insects on Earth is thought to be close to 8 million and, proportionally, scientists are closer to naming all plant and vertebrate species. Little continues to be known about the distribution and biology of vast numbers of species groups, including arthropods, fungi, and nematodes.
With technological advances, scientists have also discovered a wealth of new species in areas assumed to be barren, previously inaccessible to humans. Researchers have only recently discovered that the deep Antarctic seas are teeming with life. New species are also still being discovered in relatively well populated areas; one study found 10,000 bacterial species in a single gram of Minnesota soil.
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