Biodiversity is a numbers game. Well, it’s not really a game. Loss of biodiversity is among the most serious challenges facing humanity today, along with global warming and population growth.

Scientists are an essential part of the equation. Their field work, lab research, and publications provide the groundwork for conservationists, celebrities and legislators to promote their cause. Much of the scientists’ work is buried in details, so that only the most dramatic facts come to the public’s attention. So let’s look at some of the more striking numbers discovered by scientists to help illustrate what biodiversity is and where it’s headed. If you have your own favorite statistic, let me know and I’ll add it to the list.

7 million Total number of species, according to conservative estimates (Pimm and Raven, 2000)
1.8 million Approximate number of species already described
100 milion Upper estimate of all species on Earth (Erwin, 1982, see also May, 2010)
0 Number of known species elsewhere in the entire universe
15,000 Number of new species described each year (Dirzo & Raven 2003)
217 billion Value in dollars of the global economic value of pollination services performed by insects (Gallai et al. 2009, cited in Kearns 2010)
7,098 Number of US apple varieties cultivated prior to 1904 (Kearns 2010)
5 Percentage of those US apple varieties remaining today (ibid.)
22 Percentage of mammal species threatened with extinction (Hilton-Taylor et al. 2008, cited in Kearns 2010)
32 Percentage of amphibian species threatened with extinction (ibid.)
14 Percentage of bird species threatened with extinction (ibid.)
1000 Rate at which extinctions today exceed extinctions in the geologic past (Wilson 2002, cited in Kearns 2010)
5 Number of mass extinctions in Earth’s geologic past in the last 4.5 billion years
1 Number of mass extinctions underway right now

REFERENCES
C. Kearns. 2010. Conservation of Biodiversity. Nature Education Knowledge 1(9):7
R. M. May. 2010. Tropical arthropod species, more or less? Science 329: 41-42
N. Gallai, J. Sales, et al. 2009. Economic valuation of the vulnerability of world agriculture confronted with pollinator decline. Ecological Economics 68: 810-821
C. Hilton-Taylor, C.M. Pollock, et al. 2008. State of the world’s species. In Wildlife in a Changing World: An Analysis of the 2008 IUCN Red List of Threatened Species. eds. Vié, J., Hilton-Taylor, C. et al. 2008. Gland: International Union for Conservation of Nature.
R. Dirzo & P. Raven. 2003. Global State of Biodiversity and Loss. Annual Review Environment and Resources 28, 137-167
S. L. Pimm & P. Raven. 2000. Biodiversity: Extinction by numbers. Nature 403: 843-845
Wilson, E. O. 2002. Speciation and Biodiversity. American Institute of Biological Sciences
T. L. Erwin. 1982. Tropical forests: Their richness in Coleoptera and other Arthropod species. Coleopt. Bull. 36(l):74-75