Many free-ranging predators have to make foraging decisions with little, if any, knowledge of present resource distribution and availability1. The optimal search strategy they should use to maximize encounter rates with prey in heterogeneous natural environments remains a largely unresolved issue in ecology1,2,3. Lévy walks4 are specialized random walks giving rise to fractal movement trajectories that may represent an optimal solution for searching complex landscapes5. However, the adaptive significance of this putative strategy in response to natural prey distributions remains untested6,7. Here we analyse over a million movement displacements recorded from animal-attached electronic tags to show that diverse marine predators—sharks, bony fishes, sea turtles and penguins—exhibit Lévy-walk-like behaviour close to a theoretical optimum2. Prey density distributions also display Lévy-like fractal patterns, suggesting response movements by predators to prey distributions. Simulations show that predators have higher encounter rates when adopting Lévy-type foraging in natural-like prey fields compared with purely random landscapes. This is consistent with the hypothesis that observed search patterns are adapted to observed statistical patterns of the landscape. This may explain why Lévy-like behaviour seems to be widespread among diverse organisms3, from microbes8 to humans9, as a ‘rule’ that evolved in response to patchy resource distributions.
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This research was facilitated through the European Tracking of Predators in the Atlantic (EUTOPIA) programme in the European Census of Marine Life (EuroCoML). Funding was provided by the UK Natural Environment Research Council (NERC) grant-in-aid to the Marine Biological Association of the UK (MBA), the NERC ‘Oceans 2025’ Strategic Research Programme (Theme 6 Science for Sustainable Marine Resources), UK Defra, The Royal Society and the Fisheries Society of the British Isles. D.W.S. thanks G. Budd, P. Harris, N. Hutchinson and D. Uren for field assistance. G.C.H. thanks Ocean Spirits Incorporated, J. Houghton and A. Myers for logistical help in the field. A.S.B. thanks E. Murphy, M. Brandon, R. Saunders, D. Bone and P. Enderlein for their contributions to mooring sampling at South Georgia. NERC Plymouth Marine Laboratory provided L4 zooplankton data. This research complied with all animal welfare laws of the countries or sovereign territories in which it was conducted. D.W.S. was supported by a NERC-funded MBA Research Fellowship.
Author Contributions D.W.S. conceived and planned the study, led the data analysis and wrote the manuscript. All co-authors contributed to subsequent drafts. Field data of animal movements and/or prey distributions were collected by D.W.S., E.J.S., J.D.M., G.C.H., C.J.A.B., A.S.B., M.A.H., D.M., M.K.M., D.R., V.J.W. and R.P.W. The simulation model was conceived by N.E.H. and D.W.S. with N.E.H. writing the programming code. J.W.P. and A.J. were responsible for analysis of projections of 3D Lévy movements, M.Z.A. and E.L.C.S. coded the power spectrum analysis, C.J.A.B. completed the relative likelihood modelling, and G.C.H. and M.J.W. provided additional data analysis.
The file contains Supplementary Figures S1- S3 with Legends and additional references.
About this article
Scientific Reports (2017)