Navigation Links
Extinction of woolly mammoths may have been due to addition of a predator: Humans

The extinction of woolly mammoths and other large mammals more than 10,000 years ago may be explained by the same type of cascade of ecosystem disruption that is being caused today by the global decline of predators such as wolves, cougars and sharks, life scientists report July 1 in the cover article of the journal BioScience.

Then, as now, the cascading events were originally begun by human disruption of ecosystems, a new study concludes, but around 15,000 years ago the problem was not the loss of a key predator, but the addition of one human hunters with spears.

This mass extinction was caused by newly arrived humans tipping the balance of power and competing with major predators such as sabertooth cats, the authors of the new analysis argue. An equilibrium that had survived for thousands of years was disrupted, perhaps explaining the loss of two-thirds of North America's large mammals during this period.

"We suggest that the arrival of humans to North America triggered a trophic cascade in which competition for the largest prey was intensified, ultimately causing the large non-human carnivores to decimate the large herbivores," said Blaire Van Valkenburgh, UCLA professor of ecology and evolutionary biology and a co-author on the paper. "When human hunters arrived on the scene, they provided new competition with these carnivores for the same prey.

"The addition of humans was different from prior arrivals of new predators, such as lions, because humans were also omnivores and could live on plant foods if necessary," Van Valkenburgh said. "We think this may have triggered a sequential collapse not only in the large herbivores, but ultimately their predators as well. Importantly, humans had some other defenses against predation, such as fire, weapons and living in groups, so they were able to survive."

"For decades, scientists have been debating the causes of this mass extinction, and the two theories with the most support are hunting pressures from the arrival of humans and climate change," said William Ripple, a professor of forest ecosystems and society at Oregon State University and lead author on the paper.

In the late Pleistocene, researchers say, major predators dominated North America in an uneasy stability with a wide range of mammals: mammoths, mastodons, ground sloths, camels, horses and several species of bison. The new study cites previous evidence from carnivore tooth wear and fracture, growth rates of prey, and other factors that suggest that there were no serious shortages of food caused by environmental change 10,000 to 15,000 years ago.

The large herbivores seemed to be growing quickly, and just as quickly had their numbers reduced by a range of significant carnivorous predators, including lions, dire wolves and two species of sabertooth cats. Food was plentiful for herbivores, and the system was balanced, but it was dominated by predators.

Humans were the triggering mechanism for the extinction. After that, predators increasingly desperate for food may have driven their prey to extinction over long periods of time and then eventually died out themselves.

"We think the evidence shows that major ecosystem disruptions, resulting in these domino effects, can be caused either by subtracting or adding a major predator," Ripple said. "In the case of the woolly mammoths and sabertooth tiger, the problems may have begun by adding a predator, in this case humans."

The loss of species in North America during the late Pleistocene was remarkable; about 80 percent of 51 large herbivore species went extinct, along with more than 60 percent of large carnivores. Previous research has documented the growth rates of North American mammoths by studying their tusks, revealing no evidence of reduced growth caused by inadequate food, thus offering no support for climate-induced habitat decline.

Rather, the large population of predators such as dire wolves and sabertooth cats caused carnivores to compete intensely for food, as evidenced by heavy tooth wear.

"Heavily worn and fractured teeth are a result of bone consumption, something most carnivores avoid unless prey is difficult to acquire," Van Valkenburgh said.

Trophic cascades initiated by humans are broadly demonstrated, the researchers report. In North America, it may have started with the arrival of the first humans, but continues today with the extirpation of wolves, cougars and other predators around the world. The hunting of whales in the last century may have led to predatory killer whales turning their attention to other prey, such as seals and sea otters and the declines in sea otter populations has led to an explosion of sea urchins and the collapse of kelp forest ecosystems.

"In the terrestrial realm, it is important that we have a better understanding of how Pleistocene ecosystems were structured as we proceed in maintaining and restoring today's ecosystems," the scientists wrote. "In the aquatic realm, the Earth's oceans are the last frontier for megafaunal species declines and extinctions.

"The tragic cascade of species declines due to human harvesting of marine megafauna happening now may be a repeat of the cascade that occurred with the onset of human harvesting of terrestrial megafauna more than 10,000 years ago. This is a sobering thought, but it is not too late to alter our course this time around in the interest of sustaining Earth's ecosystems."


Contact: Stuart Wolpert
University of California - Los Angeles

Related biology news :

1. Rosewood trees face extinction amid Madagascars chaos
2. Prehistoric frogs face extinction
3. Prehistoric fish extinction paved the way for modern vertebrates
4. Polygala balansae, a new bush to Europe, at risk of extinction in Spain
5. Madagascars radiated tortoise threatened with extinction
6. Aznalcóllar disaster compared with Cretaceous mass extinction
7. Coal from mass extinction era linked to lung cancer mystery
8. Paleontologists find extinction rates higher in open-ocean settings during mass extinctions
9. Is 80-year-old mistake leading to first species to be fished to extinction?
10. Volcanoes played pivotal role in ancient ice age, mass extinction
11. Clemson researchers say algae key to mass extinctionss
Post Your Comments:
(Date:6/27/2016)... Research and Markets has announced the addition of the "Biometrics ... The report forecasts the biometrics market ... CAGR of 12.28% during the period 2016-2020. The ... inputs from industry experts. The report covers the market landscape and ... a discussion of the key vendors operating in this market. ...
(Date:6/22/2016)... , June 22, 2016  The American College of ... Trade Show Executive Magazine as one of the fastest-growing ... May 25-27 at the Bellagio in Las Vegas ... the highest percentage of growth in each of the following ... exhibiting companies and number of attendees. The 2015 ACMG Annual ...
(Date:6/22/2016)... 22, 2016   Acuant , the ... solutions, has partnered with RightCrowd ® ... Visitor Management, Self-Service Kiosks and Continuous Workforce ... add functional enhancements to existing physical access ... venues with an automated ID verification and ...
Breaking Biology News(10 mins):
(Date:6/27/2016)... -- Alex,s Lemonade Stand Foundation (ALSF), a leading national childhood ... state-of-the-art bioinformatics lab, using ,big data, to advance the ... Liz Scott , co-executive director of ALSF and ... Washington, D.C. , hosted by Vice ... of pediatric cancer research and awareness. ...
(Date:6/27/2016)... , June 27, 2016  Global demand ... 4.6 percent through 2020 to $7.2 billion.  This ... and beverages, cleaning products, biofuel production, animal feed, ... biotechnology, diagnostics, and biocatalysts). Food and beverages will ... driven by increasing consumption of products containing enzymes ...
(Date:6/27/2016)... /PRNewswire/ - BIOREM Inc. (TSX-V: BRM) ("Biorem" or "the Company") ... shareholders, Clean Technology Fund I, LP and Clean Technology ... based venture capital funds which together hold approximately 59% ... diluted, as converted basis), that they have entered into ... holdings in Biorem to TUS Holdings Co. Ltd. ("TUS") ...
(Date:6/27/2016)...  Sequenom, Inc. (NASDAQ: SQNM ), a ... the development of innovative products and services, announced today ... States denied its petition to review decisions ... U.S. Patent No. 6,258,540 (",540 Patent") are not patent ... Supreme Court,s Mayo Collaborative Services v. Prometheus Laboratories decision.  ...
Breaking Biology Technology: