Camera trap study provides photographic evidence of cougar ecological impact – Zoo House News

Camera trap study provides photographic evidence of cougar ecological impact – Zoo House News

  • Science
  • January 25, 2023
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A camera trap study of two ecosystems — one with cougars and one without — is helping scientists understand the many ways apex predators affect the abundance, diversity and habits of other animals, including smaller carnivores.

The study, reported in the journal Ecosphere, followed several members of the order Carnivora and examined how the largest carnivore in each location affected the behavior and presence of other animals in the same environment.

“No one has really looked at how the entire carnivore community changes when you lose this top predator,” said Alex Avrin, who conducted the research as an MS student at the University of Illinois Urbana-Champaign with Max Allen, a research scientist at the University of Illinois Illinois Natural, directed History Survey and Professor of Natural Resources and Environmental Sciences at the University of I. Avrin is now a Research Scientist with the California Fish and Wildlife Service.

Previous studies have shown that cougars tend to suppress populations of medium-sized carnivores like coyotes, which do their best to avoid cougars, Avrin said. Reduced coyote populations allow other medium-sized carnivores to thrive. This has a cascading effect in many other ways.

Cougars also leave behind a lot of carrion, which allows a variety of scavengers — from microbes to birds and other animals — to feed on the remains that the cougars don’t consume, Avrin said. Coyotes tend to target smaller species and eat most of what they kill, leaving less for other creatures to eat.

The researchers wanted to compare the dynamics of ecosystems with and without cougars.

“We specifically wanted to investigate whether coyotes would soar in the absence of cougars and take on this role of apex predator,” she said.

In several week- or month-long sessions between 2011 and 2019, the researchers deployed grids of motion-activated cameras at various locations in California’s southern Santa Cruz Mountains and at the massive military facility of Fort Hood, Texas. The Santa Cruz site has a healthy population of cougars, as well as bobcats, gray foxes, raccoons, striped skunks, and coyotes. Fort Hood has the same carnivorous mammals except cougars. It is also home to the eastern spotted skunk and the ringtail, a member of the raccoon family. All of these species were included in the new analysis.

“We used the photos to get an idea of ​​what species were at each site, what areas they used, and how often we spotted them,” Avrin said. “And we used a few different measures to see how the smaller carnivores behave around both cougars and coyotes.”

The two sites were similar enough to make these comparisons, “but of course the climate, human land use, and other variables differed between sites,” she said.

As expected, the analysis revealed that wherever cougars were present, coyotes were rarely seen. While other carnivores also appeared to avoid cougars, they were much more likely to be spotted by the same camera traps as cougars—just at different times. Bobcats and gray foxes also used the areas frequented by cougars more often than the researchers expected.

At Fort Hood, where there were no cougars, coyotes had a different effect on the other carnivores.

“If coyotes took the same top role as cougars, we would expect them to suppress bobcats – their next biggest competitor – and release the smaller carnivores,” Avrin said. “And what we found is that they really suppressed everything — bobcats and the other carnivores.”

The coyotes seemed to have less of a suppressive effect on the other carnivores than the cougars did on coyotes, she said.

“This is a correlational study, so we can’t say definitively that the lack of cougars caused these other effects,” she said. But the study strongly suggests that coyotes will not replace the apex predator in an ecosystem without cougars.

“So yeah, if you lose an apex predator, pretty much your entire ecosystem is going to change,” Avrin said.

“Without cougars, you’re likely to be more heavily grazed by deer, especially in areas near water, which can affect streams and other species,” she said. “Coyotes don’t have the same effect because they can’t control these larger prey populations in the same way. They are likely to suppress smaller prey populations, which then changes things in other ways.”

“This study gives us a more complete picture of the changes that occur when an apex predator disappears,” Allen said. “While many people think smaller carnivores can take the lead, we see that mesocarnivores like coyotes don’t have the same effects as a true apex predator. This underscores the importance of keeping each species in place for an intact ecology community.”

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 at the U. of I.

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