Read the following statements about the number of species on earth:
A. For many taxonomic groups, species inventories are more complete in tropical than in temperate countries.
B. An overwhelmingly large proportion of the species waiting to be discovered are in the tropics.
C. A conservative and scientifically sound estimate made by Robert May places the global species diversity at about 7 million.
D. If biochemical or molecular criteria are accepted for delineating species of prokaryotes, their diversity alone might run into millions.
How many of the above statements are correct?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Three
Nobody knows the exact number of species on earth. Biologists compare the temperate and tropical species richness of a well-studied insect group and extend this ratio to other groups to get a rough estimate. Three of the four statements match the book.
A. For many taxonomic groups, species inventories are more complete in tropical than in temperate countries. — False. It is the other way round. Inventories are more complete in temperate countries. The tropics are less studied, which is why most of the species still waiting to be discovered are there.
B. An overwhelmingly large proportion of the species waiting to be discovered are in the tropics. — True. The tropics are the richest in species and also the least fully listed, so most undiscovered species lie there.
C. A conservative and scientifically sound estimate made by Robert May places the global species diversity at about 7 million. — True. Extreme estimates go from 20 to 50 million, but May’s estimate of about 7 million is the one NCERT calls conservative and sound.
D. If biochemical or molecular criteria are accepted for delineating species of prokaryotes, their diversity alone might run into millions. — True. Usual taxonomic methods do not work well for microbes, and many of them cannot be grown in the laboratory. Using biochemical or molecular criteria, prokaryotes alone may number in millions. In the book, “this group” means the prokaryotes.
So B, C and D are correct, and A is not.
NCERT Extract:
How Many Species are there on Earth and How Many in India? – “… For many taxonomic groups, species inventories are more complete in temperate than in tropical countries. Considering that an overwhelmingly large proportion of the species waiting to be discovered are in the tropics, biologists make a statistical comparison of the temperate-tropical species richness of an exhaustively studied group of insects and extrapolate this ratio to other groups of animals and plants to come up with a gross estimate of the total number of species on earth. Some extreme estimates range from 20 to 50 million, but a more conservative and scientifically sound estimate made by Robert May places the global species diversity at about 7 million.”
How Many Species are there on Earth and How Many in India? – “It should be noted that these estimates do not give any figures for prokaryotes. Biologists are not sure about how many prokaryotic species there might be. The problem is that conventional taxonomic methods are not suitable for identifying microbial species and many species are simply not culturable under laboratory conditions. If we accept biochemical or molecular criteria for delineating species for this group, then their diversity alone might run into millions.”