ScienceDaily (June 2, 2010) — New calculations reveal that the number of species on Earth is likely to be in the order of several million rather than tens of millions. The findings, from a University of Melbourne-led study, are based on a new method of estimating tropical insect species -- the largest and one of the most difficult groups on the planet to study -- having significant implications for conservation efforts.
Insect collection. New calculations suggest that the number of species on Earth is likely to be in the order of several million rather than tens of millions. (Credit: iStockphoto/Christian Skorik)
"Our understanding of species numbers has been clouded by one group of organisms, tropical arthropods, which include insects, spiders, mites and similar organisms. Estimates for this group have ranged from a few million up to 100 million," says Dr Hamilton.
Dr Hamilton and a team of international researchers have applied probability modelling techniques (models often used in financial risk estimates) to data from numerous previous studies. They found that there is a 90% chance that there is somewhere between 2 and 7 million tropical arthropod species, with a best estimate of 3.7 million.
With the addition of approximately 50,000 vertebrates (birds, mammals, amphibians and reptiles), 400,000 plants and possibly 1.3 million other organisms (mostly microorganisms, but excluding the bacteria for which we know very little about), this leaves us with a best estimate of around 5.5 million species with whom we share planet Earth. Furthermore, the study found that there is less than a 0.001% chance that the often-quoted value of at least 30 million total species is true.
"Our study is significant in this the International Year of Biodiversity, giving us a more realistic starting point for estimating extinction rates -- a profound hurdle in conservation biology. Extinction rates are typically estimated through knowing the area of habitat that has been lost, but to know how many species have been lost, we need to know how many were present in the first place. Obviously, if we are starting with less species, we may be worse off than we thought, and also be reducing the complexity of ecosystems even faster," says Dr Hamilton.
"The findings also mean that in spite of 250 years of taxonomic research, around 70% of arthropods await description."
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© 2010 by The University of Chicago.
0003-0147/2010/17601-51753$15.00
DOI: 10.1086/652998
Quantifying Uncertainty in Estimation of Tropical Arthropod Species Richness
Andrew J. Hamilton,1,* Yves Basset,2 Kurt K. Benke,3 Peter S. Grimbacher,1 Scott E. Miller,4 Vojtech Novotný,5 G. Allan Samuelson,6 Nigel E. Stork,1 George D. Weiblen,7 and Jian D. L. Yen1
1. Department of Resource Management and Geography, University of Melbourne, Burnley Campus, 500 Yarra Boulevard, Richmond, Victoria 3121, Australia;
2. Smithsonian Tropical Research Institute, Apartado 0843‐03092, Balboa, Ancón, Panama;
3. Department of Primary Industries, 32 Lincoln Square North, Carlton, Parkville Centre, Victoria 3052, Australia;
4. National Museum of Natural History and National Zoological Park, Smithsonian Institution, Washington, DC 20013;
5. Biology Centre, Czech Academy of Sciences and Faculty of Science, University of South Bohemia, Branišovská 31, 370 05 České Budějovice, Czech Republic;
6. Bishop Museum, Honolulu, Hawaii 96817;
7. Department of Plant Biology, University of Minnesota, St. Paul, Minnesota 55108
Abstract:
There is a bewildering range of estimates for the number of arthropods on Earth. Several measures are based on extrapolation from species specialized to tropical rain forest, each using specific assumptions and justifications. These approaches have not provided any sound measure of uncertainty associated with richness estimates. We present two models that account for parameter uncertainty by replacing point estimates with probability distributions. The models predict medians of 3.7 million and 2.5 million tropical arthropod species globally, with 90% confidence intervals of [2.0, 7.4] million and [1.1, 5.4] million, respectively. Estimates of 30 million or greater are predicted to have <0.00001 probability. Sensitivity analyses identified uncertainty in the proportion of canopy arthropod species that are beetles as the most influential parameter, although uncertainties associated with three other parameters were also important. Using the median estimates suggests that in spite of 250 years of taxonomy and around 855,000 species of arthropods already described, approximately 70% await description.
Submitted November 29, 2009; Accepted March 8, 2010; Electronically published May 10, 2010
Keywords:
Coleoptera, host specificity, Latin hypercube sampling, global richness estimate, stochastic model, tropical rain forest insects.
