Sharks and other marine animals find food using a similar search pattern to the way people may shop, according to one of the largest analyses of foraging behaviour attempted so far – and the first such analysis of marine predators.
The results of the international study shows that the animals’ behaviour seems to have evolved as a general ‘rule’ to search for sparsely distributed prey in the vast expanse of the ocean. This rule involves a special pattern of random movement known as a Levy Walk, where the predators use a series of small motions interspersed with large jumps to new foraging locations. This increases the chance of finding food, however widely scattered it might be.
Dr David Sims from the Marine Biological Association and the University of Plymouth, who led the research, said, ‘Systematic searching is not the most efficient strategy if you’re looking for sparse items. If you go to the supermarket to buy eggs you look for them in one place, and if you don’t find them there you choose another location to look in. You probably won’t start at one end of the supermarket and search every aisle. Predators increase energy gain by adopting the Levy Walk, so they can travel further to find food.’
The researchers analysed the dive data from sophisticated electronic tags attached to a diverse range of marine predators, such as sharks, tuna, cod, sea turtles and penguins, in various locations around the world. They compared this data to the distribution patterns of their prey and found similarities, suggesting that the predators have evolved this search rule to get the best possible results from their foraging expeditions.
Dr Sims said, ‘We developed a computer model from the foraging data, and this confirmed that the observed patterns were indeed optimal for naturally dynamic prey fields. The search rule seems to be a general solution for success in complex and changeable environments.’
Similar movement patterns appear to be present in other species’ behaviour, including human travel dynamics, hinting that the patterns discovered by the team may be universal. If so, they could prove useful for programming robots to be more successful when collecting samples from inhospitable places such as active volcanoes, the deep sea or on other planets. Understanding the patterns could also shed new light on how early humans explored and colonised the continents.
The research involved an international collaboration of behavioural ecologists, mathematicians and engineers from the UK, USA, Australia and New Zealand. It was funded principally by the Natural Environment Research Council, Defra, the Royal Society and the Fisheries Society of the British Isles.
Journal reference: "Scaling laws of marine predator search behaviour" is published in Nature on 28 February 2008.
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