There's less life on Earth than we thought

A beetle is covered with the yellow pollen of desert sunflowers near Amboy, California. David McNew/Getty Images

The Earth may contain millions fewer species than previously thought, according to Australian led research. But that still leaves many millions more to be discovered.

Nigel Stork of Griffith University’s Environmental Futures Research Institute says the findings narrow global estimates for beetles and insects.

The research, in the journal Proceedings of the National Academy of Sciences (PNAS), features a new method of species calculation derived from samples of beetles from the collection at London’s Natural History Museum.

“It has been said we don’t know to the nearest order of magnitude just how many species with which we share the planet. Some say it could be as low as two million; others suggest up to 100 million,” says Professor Stork.

“By narrowing down how many species exist within the largest group – the insects and other arthropods — we are now in a position to try to improve estimates for all species, including plants, fungi and vertebrates.

“Understanding how many species there are and how many there might have been is critical to understanding how much humans have impacted biodiversity and whether we are at the start of, or even in the middle of, an extinction crisis.”

About 25% of all species that have been described are beetles. However, when combined with other insects the figure climbs to more than half of all described and named species on Earth.

After measuring a sample from the Natural History Museum’s worldwide collection of beetles, Professor Stork compared the mean body size with the changing body sizes of British beetles to reveal that roughly 10% of the world’s beetles have been named and described.

In the 1980s, there were just two methods of estimating species. In the case of beetles, these gave a mean of 17.5 million species and a range of 4.9 million to 40.7 million. For all terrestrial arthropods, the mean was 36.8 million and a range of 7 million to 80 million.

However, the new research shows that four current methods of estimation – dating from 2001 onwards — suggest much lower figures: a mean of 1.5 million for beetles (range 0.9 million to 2.1 million); and 6.8 million for other insects (range 5.9 million to 7.8 million).

“With estimates converging in this way, this suggests we are closer to finding the real numbers than before,” says Professor Stork.

“It also means we can improve regional species richness. For Australian fauna and flora, for example, we should be able to make better estimates of just how many species there are and which groups need more taxonomic attention.”

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