Analysis of self-overlap reveals trade-offs in plankton swimming trajectories |
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Authors: | Giuseppe Bianco Patrizio Mariani Andre W. Visser Maria Grazia Mazzocchi Simone Pigolotti |
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Affiliation: | 1.Department of Biology, Ecology Building, Lund University, 223 62 Lund, Sweden;2.Center for Ocean Life, National Institute for Aquatic Resources, Technical University of Denmark, Kavalergården 6, 2920 Charlottenlund, Denmark;3.Stazione Zoologica Anton Dohrn, Villa Comunale, 80121 Napoli, Italy;4.Departament de Fisica i Enginyeria Nuclear, Universitat Politecnica de Catalunya Edifici GAIA, Rambla Sant Nebridi 22, 08222 Terrassa, Barcelona, Spain |
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Abstract: | Movement is a fundamental behaviour of organisms that not only brings about beneficial encounters with resources and mates, but also at the same time exposes the organism to dangerous encounters with predators. The movement patterns adopted by organisms should reflect a balance between these contrasting processes. This trade-off can be hypothesized as being evident in the behaviour of plankton, which inhabit a dilute three-dimensional environment with few refuges or orienting landmarks. We present an analysis of the swimming path geometries based on a volumetric Monte Carlo sampling approach, which is particularly adept at revealing such trade-offs by measuring the self-overlap of the trajectories. Application of this method to experimentally measured trajectories reveals that swimming patterns in copepods are shaped to efficiently explore volumes at small scales, while achieving a large overlap at larger scales. Regularities in the observed trajectories make the transition between these two regimes always sharper than in randomized trajectories or as predicted by random walk theory. Thus, real trajectories present a stronger separation between exploration for food and exposure to predators. The specific scale and features of this transition depend on species, gender and local environmental conditions, pointing at adaptation to state and stage-dependent evolutionary trade-offs. |
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Keywords: | searching strategy, encounter rate, zooplankton, self-overlap, prey– predator interaction |
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