Cheetahs hold the title of the world’s fastest land animal and can reach a top speed of 112 km per hour. The Galápagos tortoise is roughly the same size as a cheetah, yet the fastest it can “run” is 0.27 km per hour.
Though it seems intuitive that bigger animals should move faster—a longer stride covers more ground—that rule of thumb doesn’t always hold up.
THE SCIENCE OF SPEED
Instead, previous research has shown that the fastest animals are not the largest or the smallest, but somewhere in the middle, like the cheetah. Yet even knowing that, scientists have had a hard time predicting how fast an animal would be without watching it run, fly, or swim. This is particularly an issue for researchers studying extinct species such as dinosaurs, and for comparing the speed of a flying or running animal to that of a swimming animal.
Myriam Hirt, an ecologist at the German Centre for Integrative Biodiversity Research, came across this problem when she tried to come up with a formula to predict animals’ speed.
“It gave me elephants that had a maximum speed of 600 kilometers per hour, which of course is not true,” she said. The African bush elephant’s actual top speed is 40 km per hour.
After examining data on animal movement, Hirt and colleagues including Ulrich Brose, an ecologist at the University of Göttingen, decided to create a new way to predict the speeds of all kinds of animals.
“I saw the same patterns, so I knew then that there had to be some kind of very basic thing that underlies the pattern,” said Hirt. That basic thing turned out to how long it takes the animal to accelerate, the researchers report Monday in the journal Nature Ecology & Evolution.
That acceleration time depends on an animal’s body mass and locomotion mode, the method it uses to move, such as running or swimming. Larger animals, for example, exhaust their muscles more quickly while accelerating, and thus top out more quickly than lighter mid-sized animals such cheetahs. These two factors explain almost 90 percent of the variation in animal speeds, the scientists found.
A cheetah can accelerate from 0 to 96.5 per hour in only three seconds, which is faster than most cars. PHOTOGRAPH BY JOEL SARTORE, NATIONAL GEOGRAPHIC CREATIVE
This research could be helpful not only for wildlife biologists, but also for paleontologists, who in the past have had to guess dinosaur speeds based on their tracks and skeletons.
For instance, Hirt and Brose’s model predicts that the Tyrannosaurus rex—one of the largest dinosaurs—was much slower than the Velociraptor.
The research team plans to continue looking at ways to improve their predictions, including adding factors such as temperature. They also want to examine if the model could predict which fast animals hunt slower ones.
“We think that predator-prey interactions can be one of the cases where we can make this very predictor useful,” said Brose. “There’s at least 40 million species on this planet, and there’s many more interactions.”
Header: Cheetahs can run up to 112 km per hour, but usually only chase their prey at about half that speed. PHOTOGRAPH BY FRANS LANTING, NATIONAL GEOGRAPHIC CREATIVE