Organization of Biodiversity

Organisms > Populations> Communities > Ecosystems> Biosphere

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Another way to think about the organization of diversity might be:

Genetic (population)

Species (and other categories)

Ecosystem
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Animal Kingdom 1,044,000

Insects (750,000), other arthropods (88,000) and molluscs (107,250)

comprise the majority of species.

Plant Kingdom 292,200

flowering plants 250,000

gymnosperms 700

ferns and fern allies 13,000

bryophytes (liverworts & mosses) 16,000

green algae 7,000

brown & red algae 5,500

Fungus Kingdom 130,000

Zygomycota 25,000

Ascomycota 30,000

Basidiomycota 25,000

Fungi Imperfecti 25,000

Lichens 25,000

Protistan Kingdom 30,000

protozoans, plant flagellates,

diatoms, water molds and slime molds

Bacteria (prokaryotic) 2,500 to many times that, probably about 200 species of cyanobacteria allthough some 7,000 have been described

Archeae (prokaryotic, extremophiles), less than 100 species described.

Total number of described species 1,468,700

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Estimates vary among authors and the above would be considered conservative. Remember, too, that these are described species and may represent only a small fraction of the extant species. Most autorities suggest that there are 7 to 10 million species. Some suggest there may be 25 million or more.

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It is clear from the table above that species are not equally distributed among the several taxonomic groups. Most of the described species, in fact, are insects and flowering plants.

Neither are they distributed equally geographically. In general, there is an increase in species from higher to lower latitudes. A large majority of the species, perhaps two-thirds, are in the tropical regions of the world.

Many organisms have a highly restrictricted geographic distribution. As much as 20 percent of plant species and an even higher proportion of animal species are confined to 0.5 percent of the Earth's surface. Such species are known as endemics and the phenomenon is endemism.