How Many Species Are There?

We know how many species have been recorded so far, because every discovered species is published and named — but how many actually exist is a far harder question. According to the IUCN (the International Union for Conservation of Nature) in 2004, the number of plant and animal species described so far is slightly more than 1.5 million. How many are still undiscovered, nobody knows for certain.

Because species inventories are more complete in temperate than in tropical countries, biologists take a well-studied group of insects, compare its temperate-to-tropical richness, and extrapolate that ratio to other groups. Extreme estimates range from 20 to 50 million, but a more conservative and scientifically sound figure by Robert May places global species diversity at about 7 million.

The Make-Up of Life

The recorded species reveal some striking patterns. More than 70 per cent of all recorded species are animals, while plants (including algae, fungi, bryophytes, gymnosperms and angiosperms) make up no more than 22 per cent.

Among animals, insects are by far the most species-rich group — more than 70 per cent of all animals. Put another way, out of every 10 animals on Earth, about 7 are insects. And the number of fungi species alone is greater than the combined total of all fishes, amphibians, reptiles and mammals. One caveat: these figures leave out prokaryotes, whose species are hard to define and often cannot be cultured — by molecular criteria their diversity alone might run into millions.

India's Share

India is exceptionally rich. Although it has only 2.4 per cent of the world's land area, its share of global species diversity is an impressive 8.1 per cent. This is what makes India one of the 12 mega-diversity countries of the world.

So far, nearly 45,000 species of plants and about twice as many animal species have been recorded from India. If we accept May's estimate that only about 22 per cent of species have been recorded, then India probably has more than 1,00,000 plant species and more than 3,00,000 animal species still awaiting discovery — many of which may go extinct before we ever find them.

A Library Burning

Completing the inventory of a country's biological wealth is a daunting task — it needs enormous numbers of trained taxonomists and a great deal of time. And the challenge is made worse by urgency: a large fraction of undiscovered species faces extinction even before we discover them.

The chapter captures this vividly with an image worth remembering — nature's biological library is burning before we have even catalogued the titles of all the books it holds.

Quick Recap

  • IUCN (2004): slightly more than 1.5 million species described; Robert May's conservative global estimate is about 7 million.
  • Over 70 per cent of recorded species are animals; plants are no more than 22 per cent.
  • Insects are more than 70 per cent of animals (7 of every 10 animals); fungi outnumber all fishes, amphibians, reptiles and mammals combined.
  • Estimates exclude prokaryotes, which are hard to define and culture.
  • India: 2.4 per cent of land but 8.1 per cent of global species — one of 12 mega-diversity countries; ~45,000 plant species and about twice as many animal species recorded.

Solved Examples — Section 2

Q1. How many species had been described so far, according to IUCN (2004)?

Answer: Slightly more than 1.5 million plant and animal species.

Q2. What is Robert May's estimate of global species diversity?

Answer: About 7 million species.

Q3. What proportion of recorded species are animals, and what proportion are insects among animals?

Answer: More than 70 per cent of recorded species are animals, and among animals more than 70 per cent are insects.

Q4. How does the number of fungal species compare with vertebrates?

Answer: The number of fungi species is more than the combined total of all fishes, amphibians, reptiles and mammals.

Q5. Why is India called a mega-diversity country?

Answer: Because although it has only 2.4 per cent of the world's land area, it holds 8.1 per cent of global species diversity, making it one of 12 mega-diversity countries.

Q6. Why do the global estimates leave out prokaryotes?

Answer: Conventional taxonomic methods do not suit microbes and many cannot be cultured in the laboratory, so their species numbers cannot be reliably counted.