Surprisingly, scientists have a better understanding of how many stars there are in the galaxy than how many species there are on Earth. Estimates of global species diversity have varied from 2 million to 100 million species, with a best estimate of somewhere near 10 million, and only 1.4 million have actually been named. The problems stemming from the limits of current knowledge of species diversity are compounded by the lack of a central database or list of the world's species.

New species are still being discovered--even new birds and mammals. On average, about three new species of birds are found each year, and as recently as 1990, a new species of monkey was discovered. Other vertebrate groups are still far from being completely described: an estimated 40 percent of freshwater fishes in South America have not yet been classified.

Scientists were startled in 1980 by the discovery of a tremendous diversity of insects in tropical forests. In one study of just 19 trees in Panama, fully 80 percent of the 1,200 beetle species discovered were previously unknown to science. At least 6 million to 9 million species of arthropods -- and possibly more than 30 million -- are now thought to dwell in the tropics with only a small fraction currently described.

As scientists begin investigating other little-known ecosystems, like the soil and the deep sea, "surprising" discoveries of species become commonplace. Small wonder. A single square meter of temperate forest can hold 200,000 mites and tens of thousands of other invertebrates. A similar-sized plot from tropical grasslands can hold 32 million nematodes, and one gram of the same soil might hold 90 million bacteria and other microbes. How many species these communities contain is still anyone's guess.

Marine systems too are revealing an unsuspected diversity. Scientists believe that the deep sea floor may contain as many as a million undescribed species. Entirely new communities of organisms -- hydrothermal vent communities -- were found less than two decades ago. More than 20 new families or subfamilies, 50 new genera, and 100 new species from these vents have been identified.

Source: Thomas, 1990; Grassle, 1989; Grassle et al., 1990 <!---

Related Articles in Print:

• Thomas, C.D. 1990. Fewer species. Nature 347:237.
• Grassle, J.F. 1989. Species diversity in deep-sea communities. Trends in Ecology and Evolution 4(1):12-15.
• Grassle, J.F., N.J. Maciolek, and J.A. Blake. 1990. Are deep sea communities resilient? Pp. 385-393 in G.M. Woodwell (ed.), The Earth in Transition: Patterns and Process of Biotic Impoverishment. Cambridge University Press, Cambridge, U.K.