Question

A statistical comparison of the temperate-tropical species richness of which of the following taxonomic groups is done to have a gross estimate of the total number of species on earth?

• A. Mammals
• B. Monerans
• C. Insects
• D. Angiosperms

Answer 1

The correct option is C Insects

More than 1.5 million species of plants and animals are known to be described by biologists but when it comes to estimating the total number of existing species on this planet, the estimates vary widely, some being mere educated guesses.

It is assumed that the species inventory in the temperate regions is more complete than in the tropics.

The climatic conditions in the tropics remain fairly constant throughout the year with no harsh extremes which makes these regions more habitable for a wide variety of different species and hence is capable of housing a relatively higher number of species than the temperate regions. Thus, it is assumed that a wider variety of species are yet to be identified in the tropics.

Fig: Graph showing the decrease in the number of bird species from tropical to temperate region

Biologists make a statistical comparison of the species richness of insects (the taxonomic group with highest species diversity) in the temperate and tropic regions. This ratio is then extrapolated to other groups of plants and animals to have a gross estimate of the total number of species that exist. A scientifically sound and more conservative estimate given by Robert May estimates the global species diversity to be at around 7 million.