Elephants in Cerrado could play role once performed by mastodons

AGÊNCIA FAPESP/DICYT Which of Earth’s continents has the most large animals? Africa, of course, but it has not always been so. Once upon a time, all continents were inhabited by large mammals weighing more than a ton, which biologists classify as megafauna. These mammals played a key role in the environment, spreading seeds from the flora of every ecosystem of which they were a part, as well as eating the vegetation and recycling nutrients through their droppings.

There were giant sloths and mastodons in South America; mammoths in North America, Asia and Europe; and giant relatives of the kangaroo as big as a hippopotamus in Australia. These species and others as large became extinct following contact with Homo sapiens.

What were the consequences of the sudden extinction of all of this megafauna? Were Brazil’s savanna-like Cerrado and Atlantic rainforest biomes any different when they were inhabited by giant mammals and birds? Would reintroduction of megafauna be a viable and efficient conservation strategy?

An international group of researchers analyzed this possibility based on a review of the literature, focusing on what they call “trophic rewilding.” A paper summarizing their work has just been published by the Proceedings of the National Academy of Sciences (PNAS).

One of the authors is Mauro Galetti, coordinator of the Graduate Program in Ecology & Biodiversity at São Paulo State University’s Bioscience Institute in Rio Claro, Brazil (IB-UNESP/RC). He is also principal investigator for FAPESP’s Thematic Project “Ecological consequences of defaunation in the Atlantic Rainforest”.

“Many people think large mammals exist or existed only in Africa, but elephants, horses, bears and others inhabited almost every part of the planet. In Australia, there were giant lizards and kangaroos. Human action in the past 50,000 years in Australia and in the past 10,000 years in the Americas has led to the extinction of almost all of these large mammals,” Galetti said.

“Researchers are reaching the conclusion that large mammals played a key role in ecosystems and probably also in the climate in the areas they inhabited. For this reason, it has been suggested that large mammals should experimentally be reintroduced into the wild, not just in Brazil but also in other places, such as the British Isles, which currently have no large mammals at all but which once had wolves, boars and bears.”

Trophic rewilding, Galetti explained, entails the reintroduction of large animals responsible for essential trophic functions whose ecological niches were left empty by the extinction of the original megafauna.

In the Cerrado, elephants and horses could perform the role once played by mastodons, giant sloths, glyptodons (giant armadillos), and herds of American horses and camels, all of which are extinct. “The Cerrado was home to a great many species of large mammals not much more than 10,000 years ago. Today’s elephant is a substitute for yesterday’s mammoth,” Galetti said.

Have trophic rewilding experiments been conducted anywhere? “Yes, in a few places, like Siberia and the Netherlands, where scientific refaunation with large mammals is being carried out. But there’s a school of scientists who believe it can be done experimentally all over the world. It isn’t simply a matter of releasing elephants into the Cerrado, but of managing large mammals in controlled environments to study their effects,” Galetti said.

Trophic rewilding should be done not in biological reserves, according to Galetti, but in controlled private areas and experimental sites. “Biological reserves should be left as they are and can’t be used for this kind of experiment,” he said. The strategy can be deployed in areas deemed worthy of biological conservation. “There’s no point in transforming existing areas.”

Studies in Brazilian biomes

The Pantanal itself is a large-scale refaunation experiment, he added. Besides native fauna, the biome contains feral pigs, cattle, and wild horses.

“Many people think the feral pig (Sus scrofa), which descended from domestic pigs brought over by Portuguese settlers in the late eighteenth century and released into the wild, should be removed from the Pantanal because it’s exotic,” Galetti said. “But we show that this species is an outstanding disperser of seeds from many plants in the Pantanal. Of course, high population density can be harmful to the environment, as with any other species.”

Whereas in the Cerrado, trophic rewilding could occur only in small experimental areas, in the Atlantic rainforest biome, the process would have to be conducted with small animals and in restored areas that are empty because of hunting, according to Galetti.

Some Atlantic rainforest refaunation projects are under way in Tijuca Park, in the heart of Rio de Janeiro City, with the reintroduction of the red-rumped agouti (Dasyprocta leporina) and the brown howler monkey (Alouatta guariba). “Many plant species depend on animals to disperse their seeds, so the agoutis and howler monkeys are helping many plants reproduce,” Galetti said.

He has proposed the implementation of a refaunation project in parts of the Cerrado destined for destruction for the purpose of growing soybeans. The idea is to ring-fence a small area, introduce zoo and circus elephants there, and study their effects as seed dispersers and plant eaters.

“It’s not just a matter of releasing elephants or horses into the wild,” Galetti said. “These areas for refaunation wouldn’t be nature reserves or stocked with exotic animals that could become invasive, let alone animals with diseases capable of affecting native species. We have plenty of information about the disasters caused when exotic animals are used in rewilding projects.”

He added that for him, refaunation is above all an opportunity to learn how the extinction of megafauna affected the climate, soil, carbon stocks, ecosystem restoration, seed dispersal, and forest fires, among other aspects.

“The Cerrado had more animals of over a ton than present-day Africa. What were the ecological consequences of their disappearance? No one knows. Most researchers think it was all shaped by fire or soil,” Galetti said.