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According to Robert May, the global species diversity is about:
While extreme estimates range from 20 to 50 million, Robert May placed a conservative and scientifically sound estimate of global species diversity at approximately 7 million (of which ~1.5 million have been described). Mark 7 million (Option 4) in 5 seconds!
Biologists have documented and cataloged over 1.5 million species according to IUCN (2004). However, an enormous fraction of biodiversity (especially in the tropics and among insects/nematodes) remains undiscovered: - Some extreme speculative calculations suggested the existence of 20 to 50 million species. - The theoretical ecologist Robert May applied rigorous insect-host specificity ratios and species-area relationships to formulate a conservative and scientifically sound estimate placing total global species diversity at approximately 7 million. - Of these estimated 7 million species, only approximately 22% have been scientifically named and recorded so far.
- 1.5 million: The number of currently cataloged/described species according to IUCN (2004), not the total global estimate. - 20 to 50 million: Extreme, highly speculative estimates made by other researchers.
Diagnose every choice: Know exactly why the right option works and why distractors fail.
Incorrect. 1.5 million is the number of already described species recorded by IUCN.
Incorrect. 20 million is the lower bound of extreme speculative estimates.
Incorrect. 50 million is the upper bound of speculative estimates.
Correct. Robert May’s scientifically sound global estimate is 7 million.
NCERT presents three distinct numbers in the same paragraph: 1.5 million (IUCN described), 20–50 million (speculative), and 7 million (Robert May). Always tie "Robert May" directly to 7 million.
"Robert May estimates global species diversity at approximately 7 million."
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