It seems like a no-brainer: When humans hunt a species, its population declines. Just ask wolves and whales. But scientists have found an unusual case where hunting actually increases population numbers. When the Aboriginal people of Australia burn swaths of land to pursue sand monitor lizards, the reptiles don’t disappear—they thrive. The phenomenon may occur in the United States as well.
The research concerns the Martu people, who live as hunter-gatherers in the deserts of Western Australia. Forty percent of the food they eat off the land comes from sand monitor lizards (Varanus gouldii), beige reptiles that can span 140 centimeters and weigh up to 6 kilograms. To hunt the creatures, which live in underground burrows, the Martu burn patches of underbrush so they can spot fresh holes and then use sticks to force the lizards out. Scientists know that such small, controlled fires can be good for the environment; regular burning prevents the buildup of dry vegetation that can help large fires spread. But the effects of these burns on animal species have been less clear.
Anthropologist Rebecca Bliege Bird of Stanford University in Palo Alto, California, was studying the hunting habits of the Martu when she became interested in how their behaviors affected the lizards. “These people have so much knowledge about the environment, and they kept saying that the lizards are more abundant in the areas that they’ve already been burning.” To see if they were right, she and her colleagues began collecting data on the density of lizards in different parts of the Great and Little Sandy deserts of Western Australia. They traveled to different spots at varying distances from Martu villages and roads—the furthest spots have been hunted the least—and counted lizards in 10-meter-by-10-meter plots. The Martu were onto something: There were almost twice as many lizards in landscapes that were most heavily hunted than in plots with little human exposure, the team reports online today in the Proceedings of the Royal Society B.
The study doesn’t provide direct evidence for why the hunted areas house more lizards. Bird speculates that burning small areas of land at different times creates a patchwork of environments—each at different stages of recovery. This diversity in land likely increases diversity in insects and other animals and seems to help lizards thrive, she says. A lapse in such small burns in many parts of Australia during the 20th century, due to pressures on the Aboriginal people to leave the desert, could be to blame for the recent extinction of many Australian species, including dozens of mammals such as types of wallabies and mice, Bird notes. “We want to look next at whether this [change] did play a role in the native mammal decline,” she says. “It’s reasonable to think that when people left, biodiversity began to change, and then huge uncontrolled fires came through and the animals died.”
The phenomenon of human behavior—and controlled fires—having a positive impact on an animal species is unlikely to be confined to the Australian desert, Bird says. She has interviewed members of native Californian tribes who believe that restrictions on their controlled burns have led to a loss in biodiversity and native California species, and an increase in diseases in organisms including native oaks, but her team hasn’t yet studied those ecosystems.
“People had speculated about the ecological consequences of the fire regime in Australia,” says Neil Burrows, a conservation scientist at the Department of Parks and Wildlife of Western Australia who was not involved in the new research. “What they’ve done in this study is provide some solid evidence that patch burning benefits at least this one species.”
The findings, he says, suggest that land management agencies should rethink the idea that less human interaction is always better for an ecosystem. Particularly in areas that have been shaped by millennia of sustainable native-human use, people can be key to maintaining certain species.