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Science.  The extinction of ancient herbivores sparked fires on a global scale

Science. The extinction of ancient herbivores sparked fires on a global scale

2018-06-25 The Age of Mammals, mural by Rudolf Zalinger. Research and Technology Policy 2016 Popular Museum of Natural History, Yale University.

Madrid, 25 (European Press)

The disappearance of megaherbivores – species such as the woolly mammoth or the giant bison – has led to a massive increase in fire activity in grasslands around the world.

In collaboration with the Utah Museum of Natural History, Yale University scientists have compiled lists of extinct large mammals and their approximate dates of extinction on four continents. The data showed that South America was the most species lost (83% of all species), followed by North America (68%). These losses were much higher than in Australia (44%) and Africa (22%).

They then compared these results with records of fire activity detected in the lake sediments. Using coal records from 410 sites around the world, which provide a historical record of regional fire activity on all continents, they found that fire activity increased after the giant carnivores were extinguished.

On the continents that lost the most herbivores (later South and North America) there was a greater increase in the extent of fire spread, while on the continents with lower rates of extinction (Australia and Africa) there were no changes in the activity of grassland fires.

“These extinctions led to a series of consequences,” said Alison Karp, a postdoctoral fellow in Yale University’s Department of Ecology and Evolutionary Biology and author of the paper: “These extinctions led to a series of consequences. Studying these effects helps us understand how herbivores shape the environment of today’s world.”

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The widespread extinction of herbivores has had a major impact on ecosystems, from the collapse of predators to the loss of fruit trees that once relied on herbivores for dispersal.

But Karp and lead author Carla Staver, associate professor of ecology and evolutionary biology at the Yale School of Arts and Sciences, wondered if there was also an increase in fire activity in the world’s ecosystems, particularly due to the buildup of dry grass, foliage, or wood caused by the loss of Giant herbivores. They found that grass fires increased in the prairie.

However, Carp and Staver note that many species of ancient explorers—such as mastodons, diprotodons, and giant sloths, which feed on shrubs and trees in wooded areas—also became extinct during the same period, but their losses were less affected by wildfires.

Grassland ecosystems around the world have changed after the loss of grazing-resistant weeds due to the loss of herbivores and an increase in fires. New pastoralists, including livestock, eventually adapted to new ecosystems.

Therefore, scientists should consider the role of grazing livestock and wild herders in mitigating fires and climate change, according to the authors.

“This work highlights the importance that pastoralists can have in determining fire activity,” Staver says. “We must pay close attention to these interactions if we are to accurately predict the future of fires.”