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Excluding random walks in the foraging behaviour of the Portunid crab Thalamita crenata: modelisation and simulation based on real data
Grüters, U.; Cannicci, S.; Vannini, M.; Dahdouh-Guebas, F. (2012). Excluding random walks in the foraging behaviour of the Portunid crab Thalamita crenata: modelisation and simulation based on real data, in: Dahdouh-Guebas, F. et al. (Ed.) Proceedings of the International Conference 'Meeting on Mangrove ecology, functioning and Management - MMM3', Galle, Sri Lanka, 2-6 July 2012. VLIZ Special Publication, 57: pp. 77
In: Dahdouh-Guebas, F.; Satyanarayana, B. (Ed.) (2012). Proceedings of the International Conference 'Meeting on Mangrove ecology, functioning and Management - MMM3', Galle, Sri Lanka, 2-6 July 2012. VLIZ Special Publication, 57. Vlaams Instituut voor de Zee (VLIZ): Oostende. ISBN 978-90-817451-6-1. xxxi, 192 pp., more
In: VLIZ Special Publication. Vlaams Instituut voor de Zee (VLIZ): Oostende. ISSN 1377-0950, more

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Document type: Summary

Keywords
    Portunidae Rafinesque, 1815 [WoRMS]; Thalamita crenata Rüppell, 1830 [WoRMS]; ISW, Kenya, Mida Creek [Marine Regions]; Marine
Author keywords
    Random walk; Circular statistics; NetLogo; R-extension

Authors  Top 
  • Grüters, U.
  • Cannicci, S.
  • Vannini, M.
  • Dahdouh-Guebas, F., more

Abstract
    Thalamita crenata is a portunid crab present in a wide range of mangrove swamps in the Indo- Pacific region. In Mida Creek (Kenya) it is living on the intertidal flat in front of the Sonneratia alba mangroves. T. crenata has a home range of approximately 5 m and is able to return to its home burrow based on visual cues and underwater landmark memory, as evidenced by previous studies. We analysed different paths walked by T. crenata and investigated distances, distance ratios and directions. This paper was not meant to confirm or reject the ability of T. crenata to home, but to exemplify how during previous research undertakings we were able to reject the hypothesis of the species’ random walk behaviour by simulating the behaviour of “random crabs”. To exclude random behaviour we programmed different model versions that resampled observed ‘turning angles’ (0 – 23°) and ‘flight lengths’ (0 – 69 cm) at random (called semi-random) or that used the full ranges (360° turning angles and up to flight lengths of 2 m). Observed angles and flight lengths relied on detailed in situ recordings of foraging behaviour of real crabs. Using traditional and circular statistics we provided evidence of significant differences between the real and the random crabs for the distance to the home burrow as a function of distance from an experimental release point resulting from a dislocation of 5 m, for the ratios of total distance covered over shortest straight distance (the ‘straightness index’), and for the homeward components, which reflect clustering around a certain direction. The simulation program that we used was written in NetLogo and analysis performed using NetLogo's BehaviourSpace and R-extension.

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