Elusive wildcats may hold the key to healthier forests in Africa

There’s a theory about what happens when a big cat sets up shop in a forest, and it’s at the center of one of the biggest fights in ecology today. The idea goes like this: when a predator, like a leopard, moves into a stretch of woodland, it starts preying on the smaller animals — in the case of a leopard, animals like bush pigs, deer and monkeys. In doing so, it creates what’s called a trophic cascade: more leopards lead to fewer plant- and seed-eating animals, allowing more plants and trees of certain species to make it to adulthood. Some theorize that even the smell of a predator makes herbivores more cautious (known as the ecology of fear), causing them to spend less time eating out in the open. A big cat may not even need to hunt to transform a forest.

Sarah Tossens, a Ph.D. researcher at the University of Liège in Belgium, has set out to discover if this idea could be true for leopards (Panthera pardus) and African golden cats (Caracal aurata), a small forest cat found only in Central and West Africa. The golden cat is so elusive that it was only photographed in the wild for the first time in 2002. In attempting to reconstruct the food web in her study sites in the Republic of Congo and Cameroon, Tossens’s preliminary results suggest that wildcats potentially lead to higher seed germination. And her work is providing new information that could help protect these at-risk species, both listed as vulnerable to extinction on the IUCN Red List.

“In very simple terms, I would say it provides evidence that [wildcats] play a major role in predator-prey dynamics, and every ecosystem is constructed on those predator-prey dynamics,” Tossens said. “And so, if those dynamics are disturbed in any way, we could imagine that ecosystem health will be damaged.”

A clearer picture

To make these connections, Tossens first had to find the wildcats. To do so, she set up 63 motion-activated camera traps across three sites: within the Republic of the Congo’s Nouabalé-Ndoki National Park; in a Forest Stewardship Council-certified sustainable logging concession just south of the park; and in another FSC-certified logging concession in southeastern Cameroon. At the two latter sites, logging removes only 7-10% of the canopy in an area over a year; that area is then left untouched for the next 30 years.

One outcome of this project was a grim one: the camera traps didn’t photograph leopards or golden cats at the site in Cameroon. Though it’s difficult to say why, Tossens pointed out that this site is much closer to large human settlements.

“That’s a big discovery, and an unfortunate one,” she said. “Those species need to have big, vast territories, and they also have high food requirements, so if the landscape is too fragmented or prey is too limited by bushmeat hunting, they cannot survive.”

In the Republic of the Congo, however, Tossens was pleasantly surprised to find leopards and golden cats at both sites. “I was super excited, because even local people do not see them regularly,” Tossens said of the golden cats, calling them “almost like ghosts.”

Though she’s still analyzing the results, the photos suggest a relatively high density of leopards: four to six individuals per 100 square kilometers, or about 10-16 per 100 square miles. For golden cats, this analysis has been a bit more challenging: though the camera traps snapped multiple shots of golden cats, it’s difficult to tell individuals apart.

The cats and the trees

The similar leopard densities between the national park and the logging concession, and the presence of golden cats in both, has important implications for these species’ protection. It suggests that when logging sites are sustainably managed, human access is limited, and the logging company prevents illegal logging and poaching, these concessions are viable habitat for the cats. In addition, some evidence suggests these forests could potentially regenerate faster with the help of local wildlife.

Jean-Louis Doucet, Tossens’s adviser at Liège, studies forest ecology and management in Central Africa, and works with logging companies to develop sustainable practices. Doucet’s research has shown that sustainable logging helps open up paths through dense forest, and allows light to reach young seedlings. As these trees grow, large herbivores can more easily reach fruit, and then spread its seeds as they travel.

“We observe that the density of elephants, gorillas and other mammals is higher after [sustainable] logging than before,” Doucet said. One of his students found that duikers, a group of small antelope species, were minimally affected by selective logging, and played a significant role in spreading fruit; another showed that gorilla droppings around their nests placed seeds in more favorable light conditions than they’d find in the undergrowth.

“But the condition is that poaching and hunting must be controlled,” Doucet added. Without poaching control, he said, these areas can become “empty forests”: they look normal, but have no seed-spreading animals. As a result, seeds germinate directly next to their mother tree, leading to poor light conditions and the potential for inbreeding.

However, scientists aren’t sure how big cats, or the lack of them, affect these same dynamics in African forests. This is part of the reason behind Tossens’s Ph.D. There’s been some work done on wildcats in other ecosystems, like bobcats (Lynx rufus) in U.S. forests, and Eurasian lynx (Lynx lynx) in European woodlands. But when it comes to cats in African forests, “to be very honest, we know very little, almost nothing,” says Marine Drouilly, the regional coordinator for wildcat research and surveys in West and Central Africa at Panthera, the global wildcat conservation NGO.

Drouilly, who’s another of Tossens’s Ph.D. advisers, pointed out that in these regions, information is limited by a lack of conservation funding, poor infrastructure, limited local scientific capacity and, at times, a lack of interest in conservation by local governments.

Part of Tossens’s research includes collecting scat to figure out what these cats are eating, allowing her to reconstruct the food web and, from there, extrapolate how cats impact plants. But after completing a global review of wildcats in trophic cascades, she learned that researchers had shown some prey reacted to a “landscape of fear.” Just the smell of a cat will cause animals to change their behavior, diet and movements to have a better shot at avoiding being eaten.

So Tossens made an unusual purchase: the chemical compound 2-phenylethylamine, which is found in high quantities in carnivore urine. (Tossens compared the scent of this compound to an intense form of housecat urine: “I had to open it every time to make my little mixture, and it was awful,” she said. “My nose was condemned for maybe an hour after.”) At eight stations in the Cameroon logging concession, where the results wouldn’t be confused by the smell of real predators, Tossens placed small perforated bottles of this compound in water within open-ended PVC tubes, each buried like periscopes in front of fruit from the sapele tree (Entandrophragma cylindricum), a fruiting mahogany species.

Tossens is still analyzing the results, but noticed that there appeared to be more seeds germinating at the stations with the chemical than at the unscented control sites. That suggests that the presence of more wildcats could, potentially, help forests regrow.

“I still need to statistically compare all my sites … but there is a potential effect and it is really, really exciting,” Tossens said.

The top-down vs. bottom-up debate

With this work, Tossens is entering into one of the more contentious debates in ecology today: whether ecosystems are shaped more from the top down, as predators influence those further down the food chain, or the bottom up, by the availability of food and other resources. Though an area of research since the 1980s, this conversation got more interesting (and more heated) in 2012. That year, researchers from Oregon State University published the first of many papers suggesting that reintroducing wolves to Yellowstone National Park created a trophic cascade. By reducing the park’s huge elk herd, the paper suggested, wolves had allowed overgrazed forests and grasslands to regrow, and recovered rivers and wetlands that had been eroded away by the herd’s hooves and their appetites — all of which brought back a surge of biodiversity, from insects to fish, beavers to bears.

Over time, other researchers have argued that the wolves’ impact was overstated: that other factors, such as bison reintroduction, hunting of elk by humans, and climate change also played a role. (One researcher recently described the effect as more of a “trophic trickle” to The New York Times.) Similar disagreements arise when researchers make claims about top-down cascades around the world.

“There are those researchers who say, ‘Not really, because all of the studies are really correlative.’ To show a causal effect is really hard,” Drouilly said. “So, they fight.”

A recent paper that she and Doucet worked on with Tossens encapsulates this: reviewing 61 studies examining trophic cascades by wild cats, they found that 80% of those studies did show direct evidence of trophic cascades related to cats, but that 77% of the studies were observational or correlative.

When Tossens explained her aim to study whether wild cats could shape forests, Drouilly knew that the topic would be both “a really interesting subject, and very tricky for a Ph.D.” Nonetheless, she knew that “even if we can’t show everything we want, we could still show interesting results, because almost nothing is done in these species.”

Indeed, just verifying where these wild cats are living, and how human activities may affect them, is important. Tossens said that forest managers in Cameroon were “not happy” to hear that there were no cats found in the logging concession, despite the restrictions that they’d put in place to qualify as an FSC-certified concession. She said she expects they may try to implement stricter policies to prevent hunting. And when Tossens returns to the Republic of Congo, she plans to present her results to managers of Nouabalé-Ndoki National Park and the logging companies to encourage them to do more for these cats.

“We see that we have leopards and golden cats there, yay, that’s very great news, but it’s still important to realize it’s only in a small portion of the concession,” she said. “[This work] can be used to say, ‘We know this place is a very important refuge for a lot of critically endangered species. Maybe the next road we create, we will take this into account.’”

Banner image: A leopard pauses in front of one of Tossens’ camera traps, set in an FSC-certified logging concession in the northern Republic of Congo. Her research found that leopards live at the same density in this carefully-managed concession as a nearby national park. Image by Sarah Tossens.

Citations:

Ripple, W. J., & Beschta, R. L. (2012) Trophic cascades in Yellowstone: The first 15 years after wolf reintroduction. Biological Conservation, 145(1) 205-213. doi:10.1016/j.biocon.2011.11.005.

Tossens, S., Drouilly, M., Lhoest, S. Vermeulen, C., & Doucet, J.-L. (2024) Wild felids in trophic cascades: A global review. Mammal Review. doi:10.1111/mam.12358.