Biodiversity: in the space of a few centuries, one in ten animal species could have become extinct

Benoît Fontaine is a research engineer. He works for the National Museum of Natural History and the French Office for Biodiversity. Along with two other researchers, he has just published a study in the scientific journal Biological Reviews which argues that the risk of mass extinction – the start of a sixth extinction since the appearance of life – is largely underestimated. To do this, the trio studied the fate of two hundred species of terrestrial molluscs. Explanations.

Why propose a different approach to the erosion of life?

There are, in the current public debate, challenges to the scientific consensus on the erosion of biodiversity…

Benoît Fontaine is a research engineer. He works for the National Museum of Natural History and the French Office for Biodiversity. Along with two other researchers, he has just published a study in the scientific journal Biological Reviews which argues that the risk of mass extinction – the start of a sixth extinction since the appearance of life – is largely underestimated. To do this, the trio studied the fate of two hundred species of terrestrial molluscs. Explanations.

Why propose a different approach to the erosion of life?

In the current public debate, there are challenges to the scientific consensus on the erosion of biodiversity caused by human pressure. They are quite similar to what we have seen for the climate: “the evidence is lacking”, “it’s not that serious”, “scientists do not agree”, all these arguments… In reality, the community of researchers is unanimous. Biodiversity is seriously threatened, as a number of studies demonstrate.

Those who refute this observation often rely on the red list of threatened species of the IUCN (International Union for the Conservation of Nature). This list is very serious. It provides valuable information on the abundance of species populations, their ranges, the importance of threats, etc. But it does not offer an exhaustive overview of animals that have disappeared over the past few centuries. We can prove the existence of an animal or plant species by observing it only once. But, conversely, never observing it, even over long periods of time, does not prove its extinction! So the IUCN is very careful before pronouncing the disappearance of a species, and it is right. If we stick to his red list, we should consider that only 0.04% of species have become extinct since the year 1500. Which would mean that there is no crisis.

What is the actual rate of extinction?

According to our analysis, it is in a range between 7.5% and 13% of the approximately two million species recorded in the world.

How to explain such a difference ?

There is a second major bias when we limit ourselves to the IUCN Red List. Above all, it lists the animals in which man is interested, those he sees in his environment: the 6,500 mammals, the 11,000 species of birds, sometimes the amphibians. Many of these species are subject to protection and restoration programs. But in doing so, it is the essence of biodiversity that is ignored: invertebrates, which represent 95% to 97% of known animal species. There are a lot of them that have been observed only once. The data concerning them is far too incomplete for them to meet the criteria of the red list. We are facing a black hole of knowledge.

How did you fix it?

We focused on land molluscs – snails – among which we tracked a sample of two hundred species, all over the planet. The observations made in the past on these species, as well as the collections of specimens in natural history museums, were listed. If a snail was spotted every ten years during the XIX^and century but was never identified again, the species must have had a problem. In contrast, another species of snail that is collected continuously to the present day is unlikely to be extinct – even if only once every fifty years on average. A mathematical model based on this logic was built. Parallel to this work, the specialists of these snails were questioned. It is “expert opinion”, pure scientific knowledge. These two independent approaches – the computer calculation and the scientist – validate each other: their results are similar. A rate of extinction of the group of molluscs close to 10% is obtained.

Can we validly extrapolate this figure to all of biodiversity?

You have to be careful. The sample, two hundred terrestrial molluscs, is limited. We must consider that there are significant differences between island biodiversity, which is restricted to a territory, and continental biodiversity, which has a better chance of adapting to a change in its environment. It is also necessary to differentiate between generalist species and those which need very specific conditions to survive and reproduce. These precautions taken, we are much closer to reality with an extinction rate of 10% than by invoking the 0.04% resulting from the interpretation of the IUCN red list!

“We scientists bring bad news but we also say it’s not too late”

Is the danger similar on land and at sea?

The general public is very aware of the dangers hanging over the ocean. Even so, the species that live there are probably less threatened. Their habitats are much less fragmented than on land. And larger ranges in general.

Is the sixth extinction inevitable?

When we take conservation measures, it works. The populations of large cetaceans recovered when we stopped hunting them. Bluefin tuna has returned to the Mediterranean. So he hadn’t completely disappeared. We scientists bring bad news but we also say that it is not too late.