Mammals become extinct much faster than they diversify

Rodiano Bonacci
Ottobre 19, 2018

The researchers say the data could be used to identify and prioritize at risk species before it's too late.

According to forecasts of climatologists, the Earth is on the verge of the sixth mass extinction, which inevitably will destroy 99.9% of the rare species of mammals, most of the flora and 66% of the species in the status of "endangered".

Like many scientists, Davis believes the world is now in the midst of a sixth mass extinction, also known as the anthropocene extinction or one caused by human activity. According to the scientists, humans and their activities have caused the extinction of at least 300 separate mammalian species.

In a study published Monday in the journal PNAS, scientists from Aarhus University in Denmark calculated how fast extinctions are happening, and how long it would take for evolution to bring Earth back to the level of biodiversity it now has.

Evolution is the planet's defense mechanism against the loss of biodiversity. As habitats and climates change, species that can't survive die, and new species slowly emerge. But it takes a long time for new species to fill the gaps - and that process is far slower than the rate at which humans are causing mammals to go extinct.

The researchers used their extensive database of mammals which included species that still exist, but also the hundreds of species that lived in the recent past and became extinct as Homo sapiens spread across the globe.

They used computers, evolutionary simulations and their huge data sets to calculate the amount of evolutionary time that would be lost from past and future extinctions and to assess how long recovery would take.

The team considered a few scenarios: mammals start to recover immediately - a situation that would require a dramatic change to conservation norms-or after 20, 50 or 100 years of current conservation efforts.

The researchers drew lessons from previous extinctions, such as the extinction of Pleistocene "megafauna" after the last ice age.

Davis said each lost species had its own intrinsic value, but the loss of the most distinct creatures was most damaging: "Typically, if you have something that is off by itself, it does some job that no other species is doing".

Paleontologist and lead researcher Matt Davis of Denmark's Aarhus University warned, "We are starting to cut down the whole tree [of life], including the branch we are sitting on right now".

He noted regenerating 2.5 billion years of evolutionary history is hard enough, but today's mammals are also facing increasing rates of extinction.

"Large mammals, or megafauna, such as giant sloths and sabre-toothed tigers, which became extinct about 10,000 years ago, were highly evolutionarily distinct", Davis said in a press release.

They inspected several scenarios, modeling the complex evolutionary relationships between existing and extinct mammals, finding that even under the most optimistic scenario, it would still take up to five million years for the mammalian life to regenerate its lost branches and twigs of the evolutionary tree. Asian elephants' chance of making it to the 22nd century is less than 33%, the study found.

Professor Jens-Christian Svenning also from Aarhus University said: "Although we once lived in a world of giants: giant beavers, giant armadillos, giant deer, etc., we now live in a world that is becoming increasingly impoverished of large wild mammalian species".

"The few remaining giants, such as rhinos and elephants, are in danger of being wiped out very rapidly".

Though their calculations regarding extinction on Earth are still dire, the scientists think their work could be used to figure out which endangered species are evolutionarily unique and represent the most important parts of evolutionary history on Earth.

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