Animals have evolved a foraging behaviour that comes close what physicists calculate is the fastest way to find hidden objects, a new study reveals.
Searching animals quickly move to the first location, then slowly search that small area, before quickly moving to another area and repeating the process.
That does not surprise biologists who have studied foraging and who say evolution should find the best strategy because it pays off in survival.
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The two-stage search process is an instinctive one evident when humans search for missing keys, for example, as well as when animals search for food. People search carefully around one location, then move quickly to another where they hope to find the missing object and search again.
That behaviour reflects the difficulty of spotting objects while moving quickly. Olivier B茅nichou at the University of Paris 6 and colleagues modelled the process as if animals moved along a straight line, switching randomly between a 鈥渕oving鈥� phase 鈥� when they cannot find objects 鈥� and 鈥渟earching鈥� phases where they hunt while doing a slow, random walk.
To find the optimum search method, the team calculated what pattern of switching between moving and searching states would find randomly placed objects in the shortest time.
Power-law relation
鈥淭he typical durations of each phase vary a lot from species to species,鈥� B茅nichou and Rapha毛l Voituriez of the Curie Institute told New 杏吧原创. For example, some large fish like tuna cruise continuously looking for prey, while ambush predators like rattlesnakes 鈥渟it-and-wait鈥� for prey. But when they plotted animal data collected by biologists, they found a power-law relation predicted by their model 鈥� the faster animals switched between states, the more time they spent moving rather than searching.
Such models are useful for relative comparisons, but are limited by their simplifying assumptions, says Howard Browman of the Institute of Marine Research in Storeb酶, Norway.
Other biologists agree foraging is a more complex process. 鈥淵ou can鈥檛 totally optimise searching for a randomly located object,鈥� says John O鈥橞rien at the University of North Carolina at Greensboro, US. Animals looking for lunch have to watch out that they do not end up as some other creature鈥檚 meal. For example, seed-eating birds look up as they hop around the ground. 鈥淲e think they鈥檙e looking for overhead predators鈥� before they stop and put their heads down to search for seeds, O鈥橞rien told New 杏吧原创.
A key issue is the constraints which animals face, such as how fast they move, how well they see, and the distribution of their prey, which determine what can be optimised, he adds. Birds, for example, search more slowly if their prey is hard to spot because its colour matches the background.
Journal reference: Physical Review Letters (DOI: 10.1103/PhysRevLett.94.198101)
