Planet Earth could be home to millions fewer species than previously thought, new research has claimed.

 

Around 16 million fewer types of beetles and 30 million fewer types of terrestrial arthropods than calculated in the 1980s could actually exist.

By developing a more accurate measurement of specie numbers, scientists hope to discover the impact humans are having on extinction levels.

A study of beetles and insects - which constitute more than half of all the world's species - by researchers from Griffith University, Australia, used a new method of creating estimates by examining body size.

Professor Nigel Stork concluded that around 10 per cent of the world's beetles had been identified by comparing the changing body size of the British beetle to the mean body size of a worldwide sample from the Natural History Museum.

The body-size approach is one of four newer methods of estimation which have come into use since 2001 - compared to two used several decades ago - which are believed to yield more precise results.

His figures have drastically lowered previous projections of total species numbers - suggesting a mean of 1.5 million types of beetles, compared to the previous estimate of 17.5 million from the 1980s.

Previously, it was believed there were approximately 36.8 million kinds of terrestrial arthropod, compared to the mean of 6.8 million suggested by new research.

Professor Stork told the Proceedings of the National Academy of Sciences, which published his paper: "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."

With the various methods of estimation all producing similar findings, there is a suggestion that the number of species worldwide could have been overestimated for decades.

"While all methods of estimating global species richness make assumptions, what is important here is that four largely unrelated methods - including the new body size method - produce similar estimates," Professor Stork added.

"With estimates converging in this way, this suggests we are closer to finding the real numbers than before."

Figures from previous decades have been refined over the years, with the overall number of species decreasing as more comprehensive lists are compiled and DNA is used to assist classification.

Dr Tom Webb, Royal Society University Research Fellow, University of Sheffield, said: "There have been efforts in the marine environment especially to standardise species lists, because for years there were different names belonging to the same things.

"There were half a million names that belonged to a quarter of a million species - there had to be a process of taxonomic cleaning up.

"Researchers also previously relied on what things looked like, but now we can look how similar things are in terms of DNA to help refine the total number of species."

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