How many organisms are there

But he said the study's conclusions were reasonable. At one end of the thing, you have birds and mammals that really are completely known. At the other end, you have just got a handful of branches and twigs. But if you do the big assumption the trees are similar, then it seems sensible. The new estimate — like those that came before it — is unlikely to be the last word. Linnaeus, in his day, was confident he had captured the entire world of living things: he named about 10, species, most of which were confined to Europe.

More modern attempts to classify the living world have sought patterns from the size of living creatures, or their location. Were there more species in hot, tropical zones or in cooler areas? And what about the ocean depths? Others focused on the relationship between species. In , Terry Erwin, a carabidologist — beetle expert — at the Smithsonian Institution in Washington, went out into the jungles of Panama, rolled some sheeting on the ground and sprayed several trees with pesticide.

He discovered the bodies of more than 1, new species of beetle from the canopy of a single type of tree. There could be as many as 30m species of insects in tropical rainforests alone, calculated Erwin.

The finding drew controversy, but Erwin defended his method against those in the latest study. Species heading faster to poles. The economic benefits of nature.

Nature target 'will not be met'. Biodiversity: Out of sight, out of mind. Science intends to tag all life. The black-capped woodnymph of Colombia was identified as recently as Now, it appears, we can. Linnaean steps.

Comparison of the fits of the hyperexponential, exponential, and power functions to the relationship between the number of higher taxa and their numerical rank. We also thank the numerous respondents to our taxonomic survey for sharing their insights. Abstract The diversity of life is one of the most striking aspects of our planet; hence knowing how many species inhabit Earth is among the most fundamental questions in science.

Author Summary Knowing the number of species on Earth is one of the most basic yet elusive questions in science. Download: PPT. Figure 1. Predicting the global number of species in Animalia from their higher taxonomy.

Table 1. Available methods for estimating the global number of species and their limitations. Table 2. Currently catalogued and predicted total number of species on Earth and in the ocean. Assessment of Possible Limitations We recognize a number of factors that can influence the interpretation and robustness of the estimates derived from the method described here. Species definitions. Changes in higher taxonomy. Figure 3.

Assessment of factors affecting the higher taxon approach. Changes in taxonomic effort. Completeness of taxonomic inventories. Subjectivity in the Linnaean system of classification.

Discussion Knowing the total number of species has been a question of great interest motivated in part by our collective curiosity about the diversity of life on Earth and in part by the need to provide a reference point for current and future losses of biodiversity. Materials and Methods Databases Calculations of the number of species on Earth were based on the classification of currently valid species from the Catalogue of Life www.

Statistical Analysis To account for higher taxa yet to be discovered, we used the following approach. Survey of Taxonomists We contacted 4, taxonomy experts with electronic mail addresses as listed in the World Taxonomist Database www.

Supporting Information. Figure S1. Completeness of the higher taxonomy of kingdoms of life on Earth. Figure S2. Sensitivity analysis due to changes in higher taxonomy.

Figure S3. Assessing the effects of data incompleteness. Figure S4. References 1. May R Tropical arthropod species, more or less? Science 41— View Article Google Scholar 2.

May R. M How many species inhabit the earth? Sci Amer 18— View Article Google Scholar 3. Storks N How many species are there? Biodiv Conserv 2: — View Article Google Scholar 4. Gaston K, Blackburn T Pattern and process in macroecology. Blackwell Science Ltd. Erwin T. L How many species are there? Conserv Biol 5: 1—4. View Article Google Scholar 6. Bouchet P The magnitude of marine biodiversity. In: Duarte C. M, editor. The exploration of marine biodiversity: scientific and technological challenges.

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H Disappearing species: a global tragedy. Futurist 8— M Bottoms up for the oceans. Nature — Lambshead P. But the inventories for other classes are woefully sparse. For instance, only 7 percent of the predicted number of fungi—which includes mushrooms and yeasts—has been described, and less than 10 percent of the life-forms in the world's oceans has been identified. What's been discovered so far are "those things that are easy to find, that are conspicuous, that are relatively large," Worm said.

So far, some 1. To calculate the percentage of unknown species, Worm and colleagues first had to answer one of the great questions of ecology: How many species live on the Earth? Previous guesses ranged from three million all the way to a hundred million.

To gain a more precise answer, the authors examined the categories into which all species are grouped. Scientists lump similar species together into a broader grouping called a genus, similar genera into a still broader category called a family, and so on, all the way up to a supercategory called a kingdom. See photos of species classification in National Geographic magazine. There are five kingdoms: animals, plants, fungi, chromists—including one-celled plants such as diatoms—and protozoa, or one-celled organisms.

Worm's team estimated the total number of genera, families, orders, classes, and phyla—a designation above class—in each kingdom. That's a relatively easy task, since the number of new examples in these categories has leveled off in recent decades. Using complex statistics, Worm and colleagues used the number of genera, families, and so on to predict Earth's number of unknown species, and their calculations gave them a number: 8. The new study "takes a hugely clever approach, and I think it's going to turn out to be a pretty important study," said Lucas Joppa , a conservation ecologist at Microsoft Research, the research branch of the software giant.

But Dan Bebber , an ecologist at the environmental group Earthwatch Institute, said the study relies on improper statistical methods.