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Environmental context explains Lévy and Brownian movement patterns of marine predators

2010; Nature Portfolio; Volume: 465; Issue: 7301 Linguagem: Inglês

10.1038/nature09116

1476-4687

Nicolas E. Humphries, Nuno Queiroz, Jennifer R. M. Dyer, Nicolas Pade, Michael K. Musyl, Kurt M. Schaefer, Daniel W. Fuller, Juerg M. Brunnschweiler, Thomas K. Doyle, Jonathan D. R. Houghton, Graeme C. Hays, Catherine S. Jones, Leslie R. Noble, Victoria J. Wearmouth, Emily J. Southall, David Sims,

Mathematical and Theoretical Epidemiology and Ecology Models

What is the best way to find food in a habitat where food sources are patchy and unpredictable? Theory suggests that organisms hunting for food should adopt a Lévy-flight search strategy, a variant of a 'random walk' in which short exploratory hops are interspersed with occasional longer trips. But when predators find themselves amid abundant food, simple erratic or 'Brownian' movement should suffice. Clear evidence for true Lévy-flight-style foraging in wild animals has proved elusive, but an analysis of a large data set of 14 species of marine predators, including sharks, marlin and tuna, now proves the point. Electronic tagging reveals that the fish use Lévy behaviour when swimming in less productive waters where prey is sparse and Brownian movement in productive habitats. What is the best way for predators to find food when prey is sparse and distributed unpredictably? Theory predicts that in such circumstances predators should adopt a Lé-flight strategy, in which short exploratory hops are occasionally interspersed with longer trips. When prey is abundant, simple Brownian motion should suffice. Now, analysis of a large data set of marine predators establishes that animals do indeed adopt Lévy-flight foraging when prey is sparse, and Brownian episodes when prey is abundant. An optimal search theory, the so-called Lévy-flight foraging hypothesis1, predicts that predators should adopt search strategies known as Lévy flights where prey is sparse and distributed unpredictably, but that Brownian movement is sufficiently efficient for locating abundant prey2,3,4. Empirical studies have generated controversy because the accuracy of statistical methods that have been used to identify Lévy behaviour has recently been questioned5,6. Consequently, whether foragers exhibit Lévy flights in the wild remains unclear. Crucially, moreover, it has not been tested whether observed movement patterns across natural landscapes having different expected resource distributions conform to the theory’s central predictions. Here we use maximum-likelihood methods to test for Lévy patterns in relation to environmental gradients in the largest animal movement data set assembled for this purpose. Strong support was found for Lévy search patterns across 14 species of open-ocean predatory fish (sharks, tuna, billfish and ocean sunfish), with some individuals switching between Lévy and Brownian movement as they traversed different habitat types. We tested the spatial occurrence of these two principal patterns and found Lévy behaviour to be associated with less productive waters (sparser prey) and Brownian movements to be associated with productive shelf or convergence-front habitats (abundant prey). These results are consistent with the Lévy-flight foraging hypothesis1,7, supporting the contention8,9 that organism search strategies naturally evolved in such a way that they exploit optimal Lévy patterns.