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Stanford biologists map recent, human-caused animal extinction trends


(EMMA COCKERELL/The Stanford Daily)

In a recent study that examined global population trends, biologists at Stanford University and National Autonomous University of Mexico found that extreme population loss is affecting species across all phylogenetic groups, both rare and common.

It’s no secret that rapid industrialization has caused flora and fauna to perish in recent decades: everyone has seen the heartbreaking image of the lonesome polar bear floating on the single piece of ice. But it’s not just the polar bears that have shouldered the burden of human overexploitation. According to the researchers, Earth has entered its sixth mass extinction with mammals, birds, reptiles, and amphibian populations all suffering at the hands of human overpopulation.

While many studies focus on species that are already known to be rare, the researchers involved (who published their findings in a paper published in May) chose to instead look at the bigger picture, analyzing population loss in a sample of 177 well-studied species and mapping the ranges of nearly 27,600 species. This allows for examination of species that seem to still be common but ones whose populations are actually slowly dwindling.

“We wouldn’t have considered the passenger pigeon as rare in 1775, but it was gone by 1810,” said Paul Erlich, professor emeritus of biology and co-author of the paper.

Erlich and other researchers involved found that a startling number of species have lost more than 80 percent of their geographic ranges. In southeast Asia, where mammals were hit particularly hard, three-fourths of all mammal species had lost 80 percent of their geographic ranges. Erlich says that this doesn’t bode well for humans, whose negligence as well as inordinately high birth rate compared to death rate has significantly contributed to climate change and resource depletion, both causative factors in the sixth mass extinction.

“We’re absolutely dependent on the plants, animals and microorganisms of the planet for our lives,” Erlich said. “This is an ethical issue  …  of whether we should be wiping out the only other living things we know about in the universe, but it’s also a very practical issue because if we wipe them out, we wipe us out.”

Case in point: honeybees supply $18 billion worth of pollination services in North America and greatly increase the quality and vitamin-content of our diets, according to Erlich. Bats also provide key natural service functions: they protect crops from pests and eat malaria-spreading mosquitos. As long as these key species continue to go extinct, civilization will continue to head for its inevitable collapse, said Erlich.

“We are eroding the capabilities of Earth to maintain life,” said lead-author and UNAM professor of ecology Gerardo Ceballos, who likened the extinction of a single species to the removal of a brick from a brick wall. While the wall will initially stay standing, the repeated removal of bricks will eventually render the wall a collapsed heap unable to perform its function.

The last mass extinction, which occurred 66 million years ago and wiped out dinosaurs, is thought to have been the result of a large asteroid’s impact with Earth (or its resulting volcanic activity). The current mass extinction is the first in which humans of any kind have been around, let alone people trying to run a complex industrial civilization, said Erlich.

Erlich and Ceballos urge students and faculty alike to take simple steps to combat climate change and species extinction — issues that are inextricably tied but that both demand immediate action. Using more recyclable goods, not buying a new phone each year and purchasing natural products are all small changes that wield immense potential for collective change.

According to Erlich, Stanford still has space for improvement, calling Stanford’s investment in fossil fuels “criminal negligence.”

“Stanford is the best university in the world, but like all the others hasn’t changed its curriculum significantly to address that society is in great peril,” Erlich said.

Each individual has the power and responsibility to protect our rapidly-changing Earth. While reversing the effects of our damaging behavior is impossible, mitigation and prevention of even more species extinction should be in the forefront of our minds, in everyday interactions but also in designing the infrastructure of the future.

“Organisms evolve to live in certain habitats,” Erlich said. “What organism evolved to live in a strip mall?”


Contact Emma Cockerell at [email protected]

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