The camera-trap study of two ecosystems — one with pumas and one without — adds to scientists’ understanding of the many ways in which apex predators influence the abundance, diversity, and habits of other animals, including small carnivores.
reported in the journal OceanThe study followed several members of the order Carnivora, looking at how each region’s largest carnivore affected the behavior and presence of other animals in the same vicinity.
Alex Averin, who led the research as a master’s student at the University of Illinois at Urbana-Champaign with Max Allen, a research scientist at the Illinois Natural History Survey and professor of natural resources and environmental sciences at the USVI. Averin is now a scientist with the California Fish and Wildlife Service.
Previous studies have shown that pumas tend to suppress groups of medium-sized carnivores like coyotes, Averin said, which do their best to avoid pumas. Declining coyote numbers allow other medium-sized carnivores to thrive. This has a cascading effect on many other species.
Pumas also leave behind plenty of carrion, Averin said, allowing a range of scavengers—from microbes to birds and other animals—to feast on the remains that pumas don’t consume. Coyotes tend to target smaller species and eat most of their kills, leaving less behind for other creatures.
The researchers wanted to compare the dynamics of ecosystems with and without pumas.
“We specifically wanted to look at whether coyotes are stepping up and filling the role of apex predator in the absence of pumas,” she said.
Over several weeks or months of sessions between 2011 and 2019, the researchers deployed networks of motion-activated cameras at various spots in California’s southern Santa Cruz Mountains and across the vast military facility at Fort Hood, Texas. The Santa Cruz site has a healthy population of pumas as well as bobcats, gray foxes, raccoons, striped skunks, and coyotes. Fort Hood has the same carnivorous mammals except for the puma. It also hosts the eastern spotted and ring-tailed skunk, a member of the raccoon family. All of these species were included in the new analysis.
“We used the images to get an idea of what species were at each site, what areas they were using, and how often we’d spotted them,” Averin said. “And we used several different measures to look at how small carnivores behave around both pumas and coyotes.”
The two sites are similar enough to make these comparisons, she said, “but of course climate, human land use, and other variables differ between sites.”
As expected, the analysis revealed that wherever pumas were found, coyotes were rarely seen. While pumas also seemed to be avoided by other carnivores, they were most likely caught by the same camera traps as pumas — just at different times. Even bobcats and gray foxes used more frequented areas of pumas than the researchers expected.
At Fort Hood, where the puma was absent, coyotes had a different effect on other carnivores.
“If coyotes hold the same major role as pumas, we would expect them to suppress bobcats—their biggest competitor—to set off smaller carnivores,” Averin said. “And what we found is that they actually suppressed everything — bobcats and other carnivores.”
She said the effect of coyotes on other carnivores appears to be less than that of coyotes on wolves.
“This is a correlational study, so we can’t definitively say that the absence of puma caused these other effects,” she said. But the study strongly suggests that coyotes do not replace the apex predator in an ecosystem lacking pumas.
“So yeah, when you lose a major predator, your whole ecosystem will change,” Averin said.
“In the absence of pumas, you would likely have intense deer grazing, especially in areas close to water, which could affect the flow of streams and other species,” she said. “Wolves, since they can’t control larger prey groups in the same way, don’t have the same effect. They likely end up suppressing smaller prey groups, which then changes things in a different way.”
“This study gives us a fuller picture of the changes that occur when an apex predator disappears,” Allen said. “While many people believe that small carnivores can move into an apex role, we see that medium animals like coyotes do not offer the same effects as a true apex predator. This highlights how important it is to keep each species in place for a healthy environment.” social communication.”
The National Science Foundation, the Gordon and Betty Moore Foundation, the US Army Engineer Research and Development Center, and the Illinois Natural History Survey supported this research. INHS is a division of the Prairie Research Institute in the United States.