Two northern white rhinosThomas Mukoya / Reuters

The more humans have flourished, the more the biggest animals have not. We have always hunted large mammals, downsizing the fauna of whatever continent we happen to visit. Mammoths, woolly rhinos, ground sloths—all gone. In slaying these giants, we have remade the world in ways that we are only starting to appreciate. We have, for example, made it easier for fear to sculpt the land.

Predators instill fear in their prey. Even without actually killing anything, their mere presence creates a state of simmering stress and unease. This anxiety influences how predators’ targets take stock of the landscape around them. Open areas, with long lines of sight and plentiful paths down which to flee, offer safety. Overgrown areas, with obscuring foliage and tripping obstacles, are dangerous. Ecologists call this the “landscape of fear”—a psychological map that prey rely on to assess the risks of their surroundings.

The landscape of fear also shapes these surroundings. Scared prey spend more time in safe zones and less time in risky ones, which in turn affects where plants get eaten, and where nutrient-rich dung gets dropped.

Elizabeth le Roux from Nelson Mandela University demonstrated this pattern through a simple experiment in South Africa’s Hluhluwe-iMfolozi Park. The major predators there, like lions and leopards, are ambush hunters that launch attacks from cover, so le Roux’s team created safe zones by removing that cover. With machetes and mowers, they chopped down trees and trimmed long grass from eight plots of land, while leaving eight similar plots untouched. They then set up motion-triggered camera traps and waited for two years, to see which species would arrive, eat, and defecate.

Sure enough, the team found that medium-sized plant eaters, like wildebeest, zebras, impalas, and warthogs, tend to congregate in the newly cleared areas. They forage slightly more often in these safe zones, and they certainly poop a lot more often there, depositing three times as much dung as in the wooded regions. These animals act as living conveyor belts, moving nutrients away from dense thickets and toward open ones.

By contrast, big plant-eaters like elephants and rhinos behave very differently. As adults, they are essentially predator-proof, thanks to their huge size and thick hides. With little to fear, they eat and poop wherever they please. Rhinos, in particular, are more likely to defecate in the wooded zones, and thereby move nutrients in the opposite direction than the smaller plant-eaters do. The invulnerability of these giants, and their apparent disregard for predators, flattens out the landscape of fear. “They completely overrode the effect of the [medium-sized] herbivores,” says le Roux.

“The study is an eye-opener,” says Liana Zanette from the University of Western Ontario, who has studied landscapes of fear extensively. A less detailed comparison between open and closed areas might conclude that there were no differences between them, and no landscape of fear. “That conclusion would be absolutely incorrect,” Zanette adds. The fearlessness of the larger animals stops the fear of the smaller ones from altering the land.

“It really illustrates the importance of studying these processes at the level of whole communities—and of having intact communities to study,” says Amanda Subalusky, an ecologist from the Cary Institute of Ecosystem Studies who has studied hippos and other megafauna. Indeed, South Africa is one of the few places in the world where the largest plant-eaters still exist in abundance, and thus one of the few places where their fear-dampening effects could be seen. “This finding is particularly important given the global loss of megafauna from even our most protected areas,” Subalusky adds.

Rhino poaching in South Africa, for example, has skyrocketed over the last decade, and more than a thousand animals have been killed in each of the last five years. As their numbers dwindle, the landscape will likely become more of a patchwork. Nutrients will become concentrated in particular areas and depleted from others, with consequences that ripple through all the local plants and animals. This world without giants will be a world shaped more by fear than fearlessness. “It would have major repercussions that we likely would not be able to predict,” le Roux says.

Humans have also killed off many of the predators that cause the landscape of fear in the first place, which might also flatten its contours. Then again, we have replaced them with a super-predator that causes more fear than any other: ourselves. “Badgers in the U.K. are terrified of people way more than any other predator,” says Zanette, referring to her own studies. “And mountain lions—animals at the top of the food chain—are terrified of us as well.”

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