New research suggests that mountain lions in the western United States play an outsize role in changing their surroundings, leading the authors of the study to suggest that the big cats are “ecosystem engineers.”
In a study published online Nov. 30 in the journal Oecologia, biologist Mark Elbroch and his colleagues demonstrate that the assortment of animals that profit from the free meals provided by the kills of mountain lions (Puma concolor) ranges from birds and mammals to insects and other invertebrates.
When the team tracked 18 lion kills in the Greater Yellowstone Ecosystem in Wyoming, they found that the dispatched prey, such as deer and elk, supported 215 species of beetles.
But Elbroch, who directs the puma program for Panthera, the global wild cat conservation organization, realized that the beetles and other scavengers weren’t just following a buffet.
“They’re communing. They’re finding their mates on these carcasses,” he said in an interview. “They’re living their entire lives from larvae to adult form on a carcass and then launching forth into the world in search of another carcass to begin that cycle all over again.”
In other words, these carcasses provide habitat for the beetles and countless other organisms observed, Elbroch said.
Scientists know that some animals have a profound effect on their environment, often changing it in ways that free up resources for other species in the ecosystem. These ecosystem engineers typically function as the bulldozers and earthmovers of the natural world: Think of elephants excavating waterholes that then slake the thirst of other animals, or beavers constructing dams to form ponds that ultimately house a wide range of fish. Mountain lions, Elbroch’s team has shown, manipulate their environment in their own unique way.
Their previous research has helped crystallize the importance of mountain lion kills to the myriad other species in the system. It revealed that the larger chunks of elk meat that pumas abandon, for example, are more important to a wider variety of species than, say, the smaller bits that a wolf pack might leave behind. In a December 2017 study published in Biological Conservation, they found that 39 species of birds and mammals visit puma kills — more scavenger species than had ever been recorded around a carcass.
Elbroch said mountain lions had evolved to kill more prey meat than they needed for feeding. As solitary hunters, they often can’t finish a 225-kilogram (500-pound) elk in one sitting. And they’re frequently forced to relinquish their prey to more formidable predators such as bears and wolves. That makes them what biologists call “subordinate apex predators.”
“They’ve evolved to survive in a world where they’re not the top predator,” Elbroch said. “The fact that they kill more than they need is benefiting their ecological communities in startling and amazing ways.”
His repeat visits to the kill sites of the big cats he tracks — an essential part of the work of a wildlife biologist who studies predators — led him to wonder how deep into the ecological web the effect of that carrion penetrated. He noticed that the birds and animals weren’t just at the carcass for the meat. Small birds would be darting around above the carcasses “picking off flying insects,” he said, and vultures would revel in the cornucopia of maggots starting their lives inside the dead animal.
“We have bears doing the same thing,” Elbroch said. “They come in and just hoover up these writhing masses of insect larvae.”
So Elbroch and his fellow researchers set up insect traps around the kills they were studying, along with a set of controls farther away, and checked them every week for several months. Among the more than 24,000 beetles from 215 species they found, 113 species need carrion to survive. And they found that the number of species, as well as of individuals, was higher around the carcasses, particularly in the first eight weeks after the kill.
“This is habitat. This is not just food resource,” Elbroch said. “It’s more than that.”
He said he also believed this subordinate part played by pumas in the American West was a widespread phenomenon. In their Biological Conservation study, he and his colleagues suggest that six other cats, including the cheetah (Acinonyx jubatus) on Africa’s savannas and the Sunda clouded leopard (Neofelis diardi) in the jungles of Borneo and Sumatra, fill similar roles, collectively covering around 43 percent of the Earth’s surface outside Antarctica.
These cats also share a history of threats from humans. They’re often scapegoated as killers of livestock. Many also inhabit a fraction of their former ranges, and the IUCN lists them all as vulnerable, except for the puma, with its listing of least concern. The Florida panther (Puma concolor coryi), a subspecies of the mountain lion, is protected as an endangered species by the U.S. government.
That’s all the more reason to demonstrate the animals’ vital place in the ecosystem, Elbroch said. Right now, he is working with a group of scientists based at Washington State University to explore the effects of puma-killed carrion on the soil chemistry of a landscape.
The team suspects that the kills of mountain lions are a critical resource, not just for scavenging mammals and birdlife, or even the invertebrates that take up residence in them, but for the plant life that anchors the ecosystem.
If their hypothesis holds, “we will have tied vertebrate scavengers, invertebrate scavengers, soil and plant communities all to these kill sites,” Elbroch said. “That would be amazing.”
John Cannon is a Mongabay staff writer based in the Middle East. Find him on Twitter: @johnccannon
Barry, J. M., Elbroch, L. M., Aiello-Lammens, M. E., Sarno, R. J., Seelye, L., Kusler, A., … & Grigione, M. M. (2018). Pumas as ecosystem engineers: ungulate carcasses support beetle assemblages in the Greater Yellowstone Ecosystem. Oecologia, 1-10.
Elbroch, L. M., O’Malley, C., Peziol, M., & Quigley, H. B. (2017). Vertebrate diversity benefiting from carrion provided by pumas and other subordinate, apex felids. Biological Conservation, 215, 123-131.