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HOW MANY KINDS
OF ORGANISMS ARE THERE?

butterflies & flowersNo one knows how many kinds of organisms -- how many species -- there are on Earth. Elsewhere we explain about "lumpers and splitters," where some experts lump bunches of different-looking populations of organisms into one species, while other experts describe each distinct population as a species all by itself.

That's one reason why it's hard to know the Earth's total number of species. Even more important is this: Many, many species -- especially in the world's rainforests and in the oceans -- simply haven't been discovered yet!

Therefore, the total number of species on Earth is variously estimated to be between 5 and 50 million or more. Only about 1.8 million have actually been described, however, and a good guess is that between 75 and 90 per cent of the Earth's species are still to be named -- and that's not even including the bacteria. In the Animal Kingdom alone between 15,000 and 20,000 new species are named each year.

Here is the most up-to-date count I can find for the number of species in each of the kingdoms of living things.

KINGDOM                             # OF SPECIES
        
Bacteria.................................... 4,000
Protoctists (algae, protozoa, etc)......... 80,000
Animals, vertebrates....................... 52,000
Animals, invertebrates.................. 1,272,000
Fungi...................................... 72,000
Plants.................................... 270,000

Total number of described species... 1,750,000
Possible # of unknown species:..... 14,000,000

From the United Nations publication: UNEP-WCMC (2000). Global Biodiversity: Earth's living resources in the 21st century. Cambridge, World Conservation Press.

Without considering microorganisms, here is another view of species numbers:

Relative Numbers of Named Species of Earth's Organisms, chart prepared by Jim Conrad

Notice how many invertebrates (insects, spiders, worms, etc.) there are -- considerably over half of all named species! Also, look at how few of us vertebrates exist. Probably the most surprising feature of the above chart, however, is that beetles account for about 22% of all named species.

SPECIES DIVERSITY

A good way to see how your own part of Earth stacks up in terms of biodiversity is to visit the Biodiversity and Worldmap page of the UK's Natural History Museum. Here the world is divided into little rectangles, with high rectangles in areas of high species diversity being shown in red, low in blue. Here you'll see that the places with highest species diversity are near the Equator (the Amazon Basin, Central America, Southeast Asia) while the areas with lowest diversity are near the North and South Poles, and in the big deserts.  Though this site counts only higher plants such as trees and grasses, it gives a good idea of general biodiversity. Another Web page, this one called Relative number of described species in major taxa, reports how many kinds of insects have been named, how many fish and trees, etc.

Though countries near the Equator receiving lots of rain have the greatest biodiversity, we who live in the US also have an enormous number of species. In a book entitled Precious Heritage: The Status of Biodiversity in the United States, Edited by Bruce A. Stein, Lynn S. Kutner, and Jonathan S. Adams (Oxford University Press, 2000), the following facts were reported:

  • More than 200,000 species are now known from the United States—a figure double the previous estimate. Nonetheless, this figure may represent fewer than half the plants, animals, and microbes yet to be discovered in the country.
  • A surprising number of life forms are more diverse in the United States than anywhere else on Earth. We are particularly rich in aquatic life such as fishes, turtles, salamanders, and mussels. More fish species are found in the Tennessee River, for example, than in all of Europe.
  • The United States also supports a more diverse collection of ecosystems than any other nation on Earth. Our nation hosts a large percentage of the world’s broadleaf forests, temperate grasslands, and Mediterranean-climate vegetation.

DIVERSITY AT RISK

The above information is exciting. However, the authors of this book point out that our nation's richness of life is not faring well. It makes these points:

  • One-third of U.S. species are at risk, aquatic life being particularly vulnerable. For instance, nearly 70% of the nation’s freshwater mussel species and over half of our crayfishes are in trouble.
  • More than 500 U.S. species are already extinct or missing. Of these, at least 100 kinds of plants and animals have disappeared forever and are presumed extinct, while another 439 are missing and feared lost.
  • Nearly 60% of the United States outside of Alaska has lost most of its natural vegetation. Habitat destruction is the main threat to our species, and the introduction of alien species is the second-most important cause for this loss.

You may also be interested in the United Nations' Global Environment Outlook, publications and videos, which look at the state of the Earth's Ecosystem.

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