Biology · Biodiversity and Conservation · NEET
Both numbers are real, but they mean different things. About 1.5 million species have been actually described and named so far (IUCN, 2004). Robert May's estimate of about 7 million is the total number of species he thinks exist on Earth, including the many not yet discovered. So: 1.5 million = counted, 7 million = estimated total by Robert May.
Robert May. NCERT says he made a more conservative and scientifically sound estimate that places global species diversity at about 7 million. If a NEET question says 'according to Robert May', the answer is 7 million. Do not confuse him with Humboldt (species-area relationship) or Ehrlich (rivet popper hypothesis).
NCERT does mention that some extreme estimates range from 20 to 50 million species. But these are called extreme, less reliable guesses. Robert May's 7 million is described as the conservative and scientifically sound estimate, so in a question asking for Robert May's value, 7 million is correct and 20-50 million are distractors.
7 million is the GLOBAL species diversity estimate for the whole Earth. It is not India's number. India, though only 2.4 per cent of the world's land area, has about 8.1 per cent of global species diversity. Keep the global estimate (7 million) separate from India's share.
Species inventories are more complete in temperate regions than in the tropics, and most undiscovered species live in the tropics. So biologists took a well-studied insect group, compared its temperate-to-tropical richness ratio, and extrapolated that ratio to other groups. This statistical method gave the gross total, and Robert May's conservative version of it is about 7 million.
According to Robert May, the global species diversity is about:
Match List I with List II. List I: A. Robert May, B. Alexander von Humboldt, C. Paul Ehrlich, D. David Tilman List II: I. Species-Area relationship, II. Long term ecosystem experiment using outdoor plots, III. Global species diversity at about 7 million, IV. Rivet popper hypothesis
Try the real previous-year questions from this chapter — each with the answer and a full solution.
About 7 million species. NCERT calls it a more conservative and scientifically sound estimate of the total number of species on Earth.
Slightly more than 1.5 million species, according to IUCN (2004). This is the recorded number, not the total estimate.
Some extreme estimates range from 20 to 50 million species, but these are considered less reliable than Robert May's conservative figure of about 7 million.
They compared the temperate-to-tropical species richness ratio of a well-studied insect group and extrapolated it to other groups of plants and animals, since most undiscovered species live in the tropics.
No. 7 million is the global estimate. India holds about 8.1 per cent of global species diversity despite having only about 2.4 per cent of the world's land area.
