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Indigenous hunters vital to robust food webs in Australia

  • A new study has found that the removal of indigenous hunters from a food web in the Australian desert contributed to the local extinction of mammal species.
  • The Martu people had subsisted in the deserts of western Australia for millennia before the government resettled them to make space for a missile test range in the 1950s.
  • A team of researchers modeled the effects of this loss, revealing that the hunting fires used by the Martu helped maintain a diverse landscape that supported a variety of mammals and kept invasive species in check.

Ecologists know that when we humans start tugging at the threads of a food web, the unraveling that results is often catastrophic to the connected species, paving the way for extinction and the invasion of exotic species.

But what happens when a group of humans that had been part of that ecosystem for thousands of years suddenly disappears?

Anthropologist Rebecca Bliege Bird and her colleagues asked that question in a new study that revealed how the resettlement of indigenous people in Australia contributed to the continent’s recent rash of mammal extinctions.

The deserts of Australia. The Martu people live in the Great and Little Sandy Deserts. Image by Lencer via Wikimedia Commons (CC BY-SA 3.0).

“I was motivated by the mystery that has occurred in the last 50 years in Australia,” Bird, a professor of anthropology at Pennsylvania State University, said in a statement.

Australia has lost 28 of its land mammals in the few hundred years since Europeans first began arriving. But, Bird added, “The extinction of small-bodied mammals does not follow the same pattern we usually see with people changing the landscape and animals disappearing.”

Instead, when indigenous peoples were removed from the equation in the mid-1900s, it led to a spike in mammal extinctions. The researchers centered their research on a group called the Martu, who lived in the Great and Little Sandy Deserts of western Australia, until the government decided to resettle them to make way for a missile test range.

A drawing of banded-hare wallabies (Lagostrophus fasciatus). Image by Charles-Alexandre Lesueur via Wikimedia Commons (Public domain).

Bird and her colleagues say they believe groups like the Martu are “knitters” of the ecosystem, they wrote in their paper, published Feb. 8 in the journal Human Ecology. For 50,000 years, hunter-gathers have subsisted in the deserts of western Australia, going after all manner of prey.

“During the pre-1950, pre-contact [with Europeans] period, Martu had more generalized diets than any animal species in the region,” Bird said. She also presented her team’s work at the American Association for the Advancement of Science meeting in Washington, D.C., on Feb. 17.

The Martu used fire on the region’s grasslands to hunt, creating a mosaic of habitats in which dingoes, kangaroos, monitor lizards and a variety of other species thrived, despite the fact that they were hunted.

A mounted burrowing bettong (Bettongia lesueur) at the Central Australian Museum. Image by Mark Marathon via Wikimedia Commons (CC BY-SA 4.0).

In the past four decades, many Martu have returned to their ancestral homeland in the desert, adopting a hybrid lifestyle that involves continuing to participate in the broader Australian economy along with taking up the mantle of their hunter-gather forebears. That return provided the researchers with an opportunity to understand the impact that humans had previously had by comparing it with this new paradigm.

They used network analysis to model the impact on the ecosystem of both the strictly hunter-gather and the hybrid lifestyles. Their findings show that the absence of the influential presence of people focused solely on living off the land significantly transformed the balance of life in the desert.

Without the Martu’s small, controlled hunting fires, wildfires were more apt to grow larger. The landscape grew more homogenous and less conducive to supporting such a breadth of small mammal species.

A pygmy mulga monitor (Varanus gilleni) at Alice Springs Desert Park. Image by Mark Marathon via Wikimedia Commons (CC BY-SA 3.0).

These changes completely wiped out some mammals, including the burrowing bettong, or boodie (Bettongia lesueur), and the banded-hare wallaby (Lagostrophus fasciatus), both marsupials. Bird’s team posits that the altered habitat made things more difficult for one of the desert’s top predators, the dingo (Canis lupus dingo). As a result, Australia’s wild dog couldn’t continue to control the invasive foxes and cats that had been introduced by European settlers as early as the 1600s.

In the end, the cascading changes touched off by removing humans fundamentally changed the character of the ecosystem.

“The absence of humans creates big holes in the network,” Bird said. “Invading becomes easier for invasive species and it becomes easier for them to cause extinctions.”

Banner image of a dingo by Brian Gratwicke via Wikimedia Commons (CC BY 2.0). 

Citation

Crabtree, S. A., Bird, D. W., & Bird, R. B. (2019). Subsistence Transitions and the Simplification of Ecological Networks in the Western Desert of Australia. Human Ecology, 1-13.

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