Sharks use math to hunt their prey: marine predators cruise the seas using fractal principles.
The great white shark in Jaws knew exactly where it was going - to the closest pair of plump legs around. But where might it head if it didn't have a tasty human snack in its sights?
A new study suggests that some sharks and other marine predators can follow strict mathematical strategies when foraging for dinner. The work, reported in the June 10 Nature, is the latest aiming to show whether animals sometimes move in a pattern called a Levy walk.
Unlike random motion--in which animals take similar-sized steps in any direction, like a drunk stumbling around--Levy walks are punctuated by rare, long forays in any direction. Draw a Levy walk on a graph, and its squiggly pattern echoes a fractal, the mathematical phenomenon whose shape remains similar no matter the viewing scale.
"Living organisms, when allowed to make freely willed decisions, seem to end up obeying some kind of mathematical law," says Gandhimohan Viswanathan, a theoretical physicist at the Federal University of Alagoas in Maceio, Brazil, who was not involved in the study.
A team led by David Sims, a researcher at the Marine Biological Association of the United Kingdom in Plymouth, looked at 14 species of open-ocean marine predators, including tuna, swordfish, marlin and sharks. Electronic tags yielded 12 million data points describing how the animals swam over 5,700 days.
Many of the animals displayed Levy behavior at least some of the time, Sims and his colleagues report--"the strongest evidence yet that these Levy patterns are exhibited by wild animals," he says. Levy behavior showed up more often in waters where plankton, fish and other food was scarce. In regions with plentiful food, random motion dominated. This observation, says Viswanathan, fits with earlier suggestions that "animals may use a Levy flight motion to improve their chances of finding prey."
Not all experts are on board. Simon Benhamou, an ecologist at the National Center for Scientific Research, or CNRS, in Montpellier, France, says that statistical errors can often suggest Levy behavior where it doesn't exist.
Sims and his team now want to probe the evolutionary history of Levy behavior--for instance by monitoring the movements of the "living fossil" known as the nautilus.