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Humans Are Wiping Out Species So Fast That Evolution Can't Keep Up

Animals
Study urges conservation push for critically endangered black rhinos. CC0 1.0

With the consequences of human activities pushing Earth into a sixth mass extinction, a team of biologists have calculated that plant and animal species are being wiped out so quickly that evolution cannot keep up.

Human activities—including pollution, deforestation, overpopulation, poaching, warming oceans and extreme weather events tied to climate change—are predicted to drive so many mammals to extinction in the next five decades that nature will need somewhere between 3 to 7 million years to restore biodiversity levels to where it was before modern humans evolved, according to an alarming new analysis published Monday in the Proceedings of the National Academy of Sciences.


The study's authors, who hail from Aarhus University in Denmark and the University of Gothenburg in Sweden, are urging drastic conservation efforts.

"It is much easier to save biodiversity now than to re-evolve it later," lead author Matt Davis of Aarhus University said in a press release.

For the study, the researchers combed through an extensive database of mammals that includes existing species and species that lived in the recent past but have gone extinct since the rise of Homo sapiens. They determined that in the 130,000 years that humans have wandered the planet, we've erased 2.5 billion years-worth of evolutionary development by driving 300 million different mammal species to extinction.

When certain species die off, much of its "phylogenetic diversity" disappears, too. For instance, as Davis explained to The Guardian, losing a few species of shrew is not as devastating as losing elephants. Losing elephants is akin to "chopping a large branch off the tree of life … whereas losing a shrew species would be like trimming off a small twig."

Davis further noted in the press release:

"Large mammals, or megafauna, such as giant sloths and saber-toothed tigers, which became extinct about 10,000 years ago, were highly evolutionarily distinct. Since they had few close relatives, their extinctions meant that entire branches of Earth's evolutionary tree were chopped off. There are hundreds of species of shrew, so they can weather a few extinctions. There were only four species of saber-toothed tiger; they all went extinct."

Worryingly, some of today's most iconic megafauna are facing increasing rates of extinction, the press release warns. Black rhinos are at high risk of becoming extinct within the next 50 years. Asian elephants have less than a 33 percent chance of lasting beyond this century.

"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," said Jens-Christian Svenning from Aarhus University in the press release.

Saving animals with the long evolutionary histories—including the black rhino, the red panda and the indri lemur—should thus be prioritized.

"This highlights species we should try to save and could help us prioritize conservation," Davis told The Guardian.

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Farms with just one or a handful of different crops encourage fewer species of pollinating and pest-controlling insects to linger, ultimately winnowing away crop yields, according to a new study.

Up to half of the detrimental impacts of the "landscape simplification" that monocropping entails come as a result of a diminished mix of ecosystem service-providing insects, a team of scientists reported Oct. 16 in the journal Science Advances.

Monocrop palm oil plantation Honduras.

SHARE Foundation / Flickr / CC BY-NC 2.0​

"Our study shows that biodiversity is essential to ensure the provision of ecosystem services and to maintain a high and stable agricultural production," Matteo Dainese, the study's lead author and a biologist at Eurac Research in Bolzano, Italy, said in a statement.

It stands to reason that, with declines in the sheer numbers of insects that ferry pollen from plant to plant and keep crop-eating pests under control, these services will wane as well. But until now, it hasn't been clear how monocultures affect the number and mix of these species or how crop yields might change as a result.

Aiming to solve these questions, Dainese and his colleagues pulled together data from 89 studies cutting across a variety of landscapes, from the tropics of Asia and Africa to the higher latitudes of northern Europe. They tabulated the number of pollinating and pest-controlling insects at these sites — both the absolute number of individuals and the number of species — along with an assessment of the ecosystem services the insects provided.

In almost all of the studies they looked at, the team found that a more diverse pool of these species translated into more pollination and greater pest control. They also showed that simplified landscapes supported fewer species of service-providing insects, which ultimately led to lower crop yields.

The researchers also looked at a third measure of the makeup of insect populations — what they called "evenness." In natural ecosystems, a handful of dominant species with many more individuals typically live alongside a higher number of rarer species. The team found as landscapes became less diverse, dominant species numbers dwindled and rare species gained ground. This resulting, more equitable mix led to less pollination (though it didn't end up affecting pest control).

"Our study provides strong empirical support for the potential benefits of new pathways to sustainable agriculture that aim to reconcile the protection of biodiversity and the production of food for increasing human populations," Ingolf Steffan-Dewenter, one of the study's authors and an animal ecologist at the University of Würzburg in Germany, said in the statement.

The scientists figure that the richness of pollinator species explains around a third of the harmful impacts of less diverse landscapes, while the richness of pest-controlling species accounts for about half of the same measure. In their view, the results of their research point to the need to protect biodiversity on and around crops in an uncertain future.

"Under future conditions with ongoing global change and more frequent extreme climate events, the value of farmland biodiversity ensuring resilience against environmental disturbances will become even more important," Steffan-Dewenter said.

Reposted with permission from our media associate Mongabay.

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