When a cougar kills, the beetles also feast
Josh Barry spent the summer of 2016 strolling through northwest Wyoming’s wildlands in search of the remnants of successful mountain lion ambushes.
At 18 carcass sites the Pace University environmental science graduate student logged the usual information large carnivore predation researchers gather: the species, sex and age of prey, how much had been eaten, and the estimated day it was killed. His main purpose, however, was to trap and survey the beetle community living in and around the rotting flesh and other remains. Concurrently, he monitored species of beetles that dwelled away from carcasses, in similar swaths of the landscape.
“We would find that the carcasses have way more types of beetles,” Barry said, “and way more beetles in general.”
The effect of a cougar-killed carcass on beetle biodiversity was dramatic: Barry collected 24,209 specimens, comprising 215 beetle species that that can be sorted into eight families. Of those, 83 percent were trapped near the carcasses as opposed to the control sites, a disparity that suggests lions have a “large” to “very large” effect on beetle assemblages, statistically speaking.
Publishing his research in a recent edition of the academic journal Oecologia, Barry made the case that pumas are “ecosystem engineers,” influencing the environment and promoting biodiversity just like beavers do when they dam drainages.
“An ecosystem engineer, without anything else,” Barry said, “it’s an animal that creates or maintains a habitat and increases species richness, whether that benefits them or not.”
He drew a parallel to the Arctic fox, an animal whose defecation and prey remains around den sites fertilizes the tundra and creates hot spots of plant diversity.
The theory that lions are ecosystem engineers builds on past research that came out of the Teton Cougar Project, which is under the umbrella of the international wildcat advocacy group Panthera. The long-running study included several side projects that helped quantify how lions influence the food web, attracting scavengers and other large carnivores. There’s even an analysis underway that examines how carcasses enrich soils, growing more nutritious plants.
“The second you turn a deer into a dead deer, you have all these unexpected and additional linkages in the food web,” Panthera Puma Program Director Mark Elbroch said. “Suddenly, chickadees and red squirrels are linked to deer, because they’re actually eating it.”
Lion predation, he said, allows nutrients to move across trophic levels that they couldn’t otherwise transcend, spreading energy across the ecosystem and promoting resilience.
Elbroch, a co-author in Barry’s paper, was initially interested in assessing insect use of cougar kill sites generally, but opted to narrow the focus to beetles because the invertebrate diversity was “overwhelming.”
The former Jackson Hole resident recalled carcasses from his years in the field that appeared to be “writhing masses of insects,” and footage from motion-activated cameras that were tripped by “waterfalls of maggots.”
Fastidious cats, he said, sometimes look like they “just can’t deal with it” and will leave, seemingly grossed out, but bears and vultures will take advantage, slurping up maggots and bugs.
Mountain lion predation may have an outsized influence on biodiversity at carcass sites compared to ungulate remains left by other large carnivores. The reason is because of the large cat’s solitary nature, and its tendency to cache large prey, which takes longer to break down.
Although there were some smaller-bodied deer and a bighorn sheep encountered, elk carcasses that Barry assessed topped out at over 500 pounds. There were huge variations in beetles’ use of the carcasses over time, with the highest diversity and number coming immediately after the prey went down.
“Some carcasses, on average, had over 700 beetles in the first week alone,” Barry said.
Beetle numbers didn’t sag to the level documented at the control sites until the eighth week of decomposition, though even past that point the types of species documented were being influenced by the carcasses.
Although there were 215 beetle species detected, one type in particular was dominant. A large-bodied, fresh meat-eating species called the northern carrion beetle possesses exceptional sensory abilities that allow them to detect carcasses early and monopolize space.
Other beetle types didn’t show up until late in the game, when carcasses were broken down and difficult to discern. Those species might specialize in scavenging and breaking down hair or bone.
“Even months later beetles were coming to kills,” Barry said, “which is just fascinating.
“This hasn’t really been done before, as far as looking at how a predator affects insect communities at this level,” he said. “It was really exciting seeing all that.”