Biodiversity and species loss - 6th mass extinction

Learn more about the ongoing mass extinction

Earth has supported life for 3.5 billion years, but its hospitality is hardly consistent. Natural disasters have triggered at least five mass extinctions in the past 500 million years, each of which wiped out between 50 and 90 percent of all species on the planet. The most recent occurred about 65 million years ago, when an asteroid ended the reign of dinosaurs and opened new doors for mammals.

Now it's happening again. A 2015 study reported the long-suspected sixth mass extinction of Earth's wildlife is "already underway." And a new study calls the loss of that wildlife a “biological annihilation” and a “frightening assault on the foundations of human civilization.” Researchers from the Universidad Nacional Autónoma de México found that the rate of population loss is extremely high — even among species that are not considered endangered. They also found that up to half of all individual animals have been lost in the last few decades.

A 2016 study published in the journal Science also suggests this sixth mass extinction is killing off large ocean dwellers (like sharks, whales, giant clams, sea turtles and tuna) in disproportionately greater numbers than smaller animals. That's a reversal from past extinctions, when there was a slight connection between smaller size and going extinct.  And while previous extinctions were often linked to asteroids or volcanoes, this one is an inside job. It's caused mainly by one species — a mammal, ironically. The current crisis is the handiwork of humans, and we have a "unique propensity to cull the largest members of a population," the authors of the 2016 study write.

Many scientists have been warning us for years, citing a pace of extinctions far beyond the historical "background" rate. Yet critics have argued that's based on inadequate data, preserving doubt about the scope of modern wildlife declines. To see if such doubt is justified, the 2015 study compared a conservatively low estimate of current extinctions with an estimated background rate twice as high as those used in previous studies. Despite the extra caution, it still found species are disappearing up to 114 times more quickly than they normally do in between mass extinctions.

Here are six important things to know about life in the sixth mass extinction:

1. This isn't normal.

Extinction is a natural part of evolution, having already claimed an estimated 99 percent of all species in Earth's history. But things can get ugly when too many species die out too quickly, creating a domino effect capable of bringing down ecosystems. In the new study, researchers used a background rate of two mammal extinctions per 10,000 species per 100 years (2 E/MSY), which is double the background rate used in many previous studies. When they compared that to a conservative estimate of modern-day extinctions, they found no way to avoid calling this a mass extinction.  Even under our assumptions, which would tend to minimize evidence of an incipient mass extinction, the average rate of vertebrate species loss over the last century is up to 114 times higher than the background rate," the study's authors write. "Under the 2 E/MSY background rate, the number of species that have gone extinct in the last century would have taken, depending on the vertebrate taxon, between 800 and 10,000 years to disappear. These estimates reveal an exceptionally rapid loss of biodiversity over the last few centuries, indicating that a sixth mass extinction is already under way.

2. Space is at a premium.

The No. 1 cause of modern wildlife declines is habitat loss and fragmentation, representing the primary threat for 85 percent of all species on the IUCN Red List. That includes deforestation for farming, logging and settlement, but also the less obvious threat of fragmentation by roads and other infrastructure.

And even where habitats aren't being razed or divided, they're increasingly altered by other human activities. Invasive species now threaten a variety of native plants and animals around the world, either by killing them directly or by outcompeting them for food and nest sites. Pollution is pervasive in many places, from chemicals like mercury that accumulate in fish to the plastic debris that slowly kills sea turtles, sea birds and cetaceans. Entire ecosystems are now migrating due to climate change, leaving behind less mobile or adaptable species. And in some parts of the world, poachers are obliterating rare species to meet demand for wildlife parts like rhino horn and elephant ivory.

3. Vertebrates are vanishing.

The number of vertebrate species that have definitely gone extinct since 1500 is at least 338, according to the new study.  Even under the most conservative estimates, the extinction rates for mammals, birds, amphibians and fish have all been at least 20 times their expected rates since 1900, the researchers note (the rate for reptiles ranges from 8 to 24 times above expected). Earth's entire vertebrate population has reportedly fallen 52 percent in the last 45 years alone, and the threat of extinction still looms for many — including an estimated 41 percent of all amphibian species and 26 percent of mammals. 

4. It's probably still worse than we think.

The new study is intentionally conservative, so the actual rate of extinctions is almost certainly more extreme than it suggests. "We emphasize that our calculations very likely underestimate the severity of the extinction crisis," the researchers write, "because our aim was to place a realistic lower bound on humanity's impact on biodiversity."  The study also focuses on vertebrates, which are typically easier to count than smaller or subtler wildlife like mollusks, insects and plants. 

5. No species is safe.

Humans are hardly an endangered species, with a global population of about 7.2 billion and growing. But fortunes can change quickly, as we've demonstrated in recent decades with lots of other wildlife. And despite our best efforts to buffer ourselves against the whims of nature, civilization remains reliant on healthy ecosystems for food, water and other resources. Adjusting to mass extinctions would be a challenge under any circumstances, but it's especially daunting in the context of climate change.

6. Unlike an asteroid, we can be reasoned with.

Previous mass extinctions may have been inevitable, but it's not too late to stop this one. While the authors of the new study acknowledge the difficulty of curbing lucrative destruction like deforestation, not to mention climate change, they note it is still possible. It's even gaining momentum, thanks to growing public awareness as well as high-profile attention from governments, corporations and even the Pope.

The National Academy of Sciences

Read the peer-reviewed paper titled "Biological Annihilation via the ongoing 6th mass extinction of vertebrates" published July 26, 2017.

Read the full paper






Rob Stewart is an award winning wildlife photographer, filmmaker, conservationist and educator. Born and raised in Toronto, Canada, Stewart began photographing underwater when he was 13. By the age of 18 he became a scuba instructor trainer and then moved on to earn a Bachelor of Science degree in Biology, studying in Ontario, Jamaica and Kenya.

Before making Sharkwater (2007), Stewart spent four years travelling the world as chief photographer for the Canadian Wildlife Federation’s magazines. Leading expeditions to the most remote areas of the world, Stewart’s highly sought after images have appeared in nearly every media form worldwide. 

While on assignment to photograph sharks in the Galapagos Islands, Stewart discovered illegal longlining, killing sharks within the marine reserve. He tried promoting awareness through print media, but when the public didn’t respond, Stewart decided to make a film to bring people closer to sharks. At the age of 22 he left his photography career behind and embarked on a remarkable journey over four years and 12 countries, resulting in the epic Sharkwater.

Sharkwater (8.0 on IMDB and Rotten Tomatoes) was released by Alliance Atlantis, Warner Bros., Disney and MK2 – and has been hugely successful, premiering at the Toronto International Film Festival and winning a “Canada’s Top Ten” award. Sharkwater made history with the largest opening weekend of any Canadian documentary, and was the most award-winning documentary of the year, winning over 40 awards at prestigious film festivals around the world. Sharkwater is credited as being the genesis for the shark conservation movement, changing government policy worldwide, and inspiring the creation of shark conservation groups.

Stewart’s second film Revolution (7.6 on IMDB and 67% on Rotten Tomatoes) brought the “evolution of life and the revolution to save us” to the public, was the highest grossing Canadian documentary in 2013, was released by D films, and has won 19 awards at film festival all around the world.

Stewart has written two award winning books – Sharkwater: An Odyssey to Save the Planet (Key Porter Books), and Save the Humans (Random House).

Learn More about Rob Stewart

Rob Stewart was an inspiration, he was a marine biologist, shark advocate and documentary filmmaker.  His life tragically ended in during a diving accident while makng his last film in the Florida Keyes in 2017.

One planet, one love.

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