Biodiversity

1. What is Biodiversity?

What is biological diversity ? In its narrowest sense this term refers to the number of species on the planet, and it also is used more broadly as an umbrella term. Biological diversity refers to the variety and variability among living organisms and the ecological complexes in which they occur. Diversity can be defined as the number of different items and their relative frequency. For biological diversity, these items are organized at many levels, ranging from complete ecosystems to the chemical structures that are the molecular basis of heredity. Thus, the term encompasses different ecosystems, species, genes, and their relative abundance (Office of Technology Assessment, 1987). Or to paraphrase: number and variety of species, ecological systems, and the genetic variability they contain.
The simplest representation is:
 

Group	Number of Described Species
Bacteria and blue-green algae	4,760
Fungi	46,983
Algae	26,900
Bryophytes (mosses and liverworts)	17,000
Gymnosperms (conifers)	750
Angiosperms (flowering plants)	250,000
Protozoans	30,800
Sponges	5,000
Corals and Jellyfish	9,000
Roundworms and earthworms	24,000
Crustaceans	38,000
Insects	751,000
Other Arthropods and minor invertebrates	132,461
Mollusks	50,000
Starfish	6,100
Fishes (teleosts)	19,056
Amphibians	4,184
Reptiles	6,300
Birds	9,198
Mammals	4,170
Total	1,435,662

Three pie charts (number of species of all kinds, number of animal species, number of plant species) show the same information diagramatically.



These numbers reflect a huge amount of scientific study. In order for a species to be included on the above list, it was examined by a specialist, who carefully compared its features to those of all similar species. Then, once satisfied that the species in hand was different from all known forms, the specialist published a thorough description including drawings, counts of hairs along forelegs, length of measurable parts such as limbs and antennae, photographs, etc. The new species has then been described, and is added to our list of "known" species.
Remarkably, our estimates of the number of unknown species greatly exceed our count of the number of known species. Most experts estimate the world's species diversity at 10 to 30 million, but that is very approximate. Only 1.4 million species are "known to science" -- meaning that they have been classified by a specialist. The estimates of 10 to 30 million species are based on expert opinion of how many species are yet to be formally identified. One study of insects in the forest canopy found 5 out of 6 to be new species. Even vertebrates are not completely known -- it is estimated that nearly half of the freshwater fishes of South America are undescribed. New finds are made continuously in the tropics, and exploration of deep-sea hydrothermal vents recently led to the discovery not just of new species, but of new life forms at the family level (20 families or sub-families). When you consider that virtually every species has its own parasite, and how many groups such as nematodes and bacteria have yet to be well-studied, it is apparent that the estimates of 10 to 30 million are not out of line.
 

The global distribution of biodiversity -- its geography -- is interesting in its own right, and relevant to conservation. Biological diversity is greatest near the equator, and declines towards higher latitudes . Tropical rain forests are especially known for their exceptional diversity. Some locations known as "hotspots" harbour an unusually rich local diversity, perhaps because conditions favour evolutionary diversification.