Mammals on Earth will ‘need millions of years’ to recover

As the sixth mass extinction event in the life of the planet is upon us, great numbers of mammalian species in the wild are set to die out in coming decades. In fact, the current man-made wildlife extinction crisis is so severe that the planet will need anywhere between 3 and 5 million years to rejuvenate the loss of biodiversity in mammals.

So say three scientists from Aarhus University in Denmark, who predict that 99.9% of critically endangered species and 67% of endangered species will be gone from the wild for good within a century. Large mammals, from pangolins to tigers, are especially at risk from going extinct.

Biodiversity is more than the number of species on Earth. It is also the amount of unique evolutionary history in the tree of life,” write the three scientists who have published a new study. “We find that losses of this phylogenetic diversity (PD) are disproportionally large in mammals compared with the number of species that have recently gone extinct. This lost PD can only be restored with time as lineages evolve and create new evolutionary history.”

Because of their slow reproductive rates and small numbers of offspring, many critically endangered and endangered large mammals won’t be able to recover from mad-made threats to their existence in the wild from continuing habitat loss to poaching. Unless, that is, conservation efforts globally are stepped up to save endangered mammals before it’s too late.

“Without coordinated conservation, it will likely take millions of years for mammals to naturally recover from the biodiversity losses they are predicted to endure over the next 50 [years],” the scientists write. “However, by prioritizing PD in conservation, we could potentially save billions of years of unique evolutionary history and the important ecological functions they may represent.”

Nature, the scientists posit, will need at least 3 million years to return to today’s level of already much-diminished biodiversity if we continue losing species for another 50 to 100 years at the rate we have been losing them over the past decades and centuries. It will take up to 7 million years for biodiversity to return to the level it was before humans started having a marked impact on the planet a few thousand years ago.

“We now live in a world that is becoming increasingly impoverished of large wild mammalian species,” Prof. Jens-Christian Svenning, an expert on megafauna, said in a press release. “The few remaining giants, such as rhinos and elephants, are in danger of being wiped out very rapidly.”

Animals like black rhinos and Sumatran rhinos that are facing the threat of extinction have little chance of surviving in the wild. Even Asian elephants may not make it through the next century with their chances of survival rated at only 33% by the experts.

Nor will today’s unique species, once they’ve been driven extinct, simply re-evolve over time. They will have been gone forever from the face of the planet. Instead, other newly evolved species will take their place in a kaleidoscope of species very different from that on Earth today.

“Large mammals, or megafauna, such as giant sloths and sabre-toothed tigers, which became extinct about 10,000 years ago, were highly evolutionarily distinct,” Matt Davis, the study’s lead author, said in a press release. “Since they had few close relatives, their extinctions meant that entire branches of Earth’s evolutionary tree were chopped off.”