Intrinsic Lévy behaviour in organisms – searching for a mechanism

Abstract

Please cite this article in press as: Sims DW. Intrinsic Lévy behaviour in organisms -searching for a mechanism. Phys Life Rev (2015), http://dx.doi.org/10. 1016/j.plrev.2015.06.002 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Physics of Life Reviews 2015Intrinsic Lévy behaviour in organisms -searching for a mechanism Comment on "Liberating Lévy walk research from the shackles of optimal foraging" by A.M. Reynolds The idea that organism search strategies naturally evolved to exploit optimal Lévy patterns has gathered pace in recent years [5,7,9,11]. To account for observed Lévy-like behaviour -by which I mean behaviour patterns well approximated by a truncated Lévy distribution -it has been hypothesized that (i) scale-free activities may arise from intrinsic processes [9,11,[13][14][15][16], (ii) that behavioural adaptations to changes in environmental resources may cue the switching between localized Brownian and Lévy random searching [5,7], or (iii) that sensory interactions with heterogeneous environments may give rise to Lévy movement patterns (an emergent phenomena) [17,18]. However, the origins of such potential mechanisms remain elusive. Physics of Life Reviews 2015The review by Reynolds [19] is a timely synthesis of this burgeoning topic. The review proposes that the Lévy flight foraging hypothesis may be too narrowly focused on optimal foraging to be ideal for framing questions aimed at exploring how scale-free movements and behaviours may arise. I do not entirely agree with this position. I hold the view that to understand the mechanisms underlying the observed scale-free (Lévy) patterns it will be necessary to consider both intrinsic and extrinsic processes, in addition to behavioural adaptations that are flexible and including cognitive processes such as learning and sociality. In my opinion a new hypothesis would be particularly valuable if it could unify these different aspects. Whilst I appreciate that the LFF hypothesis may not achieve this aim for all behaviour patterns observed, it is evident that the free hypothesis outlined [19] does not succeed entirely in this endeavour either.The LFF hypothesis essentially considers natural selection as a driver for widely observed Lévy search patterns of organisms. In this idea it is the competition occurring between individuals that favours the survival of those approaching or exhibiting optimal Lévy searches (for resources such as food or mates) [3]. Reynolds [19] proposes a new synthesis supporting a new hypothesis -the 'free Lévy flight hypothesis' -which states that "Lévy flights emerge spontaneously and naturally from innate behavi...

Rationalizing spatial exploration patterns of wild animals and humans through a temporal discounting framework

“…Additionally, we extended our model to show that for foragers in the wild with noisy temporal perception, the exponent of the best fit power law is governed by the nonlinearity of time perception and the amount of competition faced from other foragers. Thus, we contribute to the ongoing discussion regarding the mechanistic origins of power law path lengths in foragers (47)(48)(49)(50)(51)(52)(53)(54)(55)(56)(57)(58) by arguing that search patterns are unlikely to be purely random when cognitive modeling is advantageous and that approximate power law path lengths emerge due to the temporal discounting of farther away rewards. A deeper understanding of the neurobiological basis of spatial search (59)(60)(61)(62)(63) may further enrich this model and provide greater insight into the movements of wild animals and humans.…”

Venturing beyond the Lévy flight foraging hypothesis: Reply to comments on “Liberating Lévy walk research from the shackles of optimal foraging”

“…Sims [9] notes that some behavioural transitions, for example, switching between intensive and extensive modes of searching in C. elegans, can be heritable traits modifiable by the environment. This point is made explicitly in my Review [10]. There I suggested that mussels Mytilus edulis and the Australian desert ant Melophorus bagoti are perhaps the only known examples of selection for Lévy walking.…”

“…The former predicts that Lévy walks will be common amongst probabilistic foragers, a prediction that I find to be incorrect. The later predicts that the occurrence of Lévy flights is accidental and uncommon even amongst probabilistic foragers and not restricted to searching, just as appears to be the case [10]. Sims [9] notes that some behavioural transitions, for example, switching between intensive and extensive modes of searching in C. elegans, can be heritable traits modifiable by the environment.…”

“…view but maintain that selection is not working with a blank canvas, as Lévy walks (usually of the variety reported to optimize random searching) can and do arise freely [10]. Once generated they may be maintained by selection or as Focardi [5] remarked be like the "spandrels of St Mark" without biological relevance.…”

“…It was also reported that molecular transport machinery operating within cells perform Lévy walks and that these Lévy walks may be attributed to selection for optimized searching [19]. Nonetheless, these 4 examples seem to be exceptions rather than the rule because most putative mechanisms for Lévy walking, such as the one that may operate in marine predators, do not require fine tuning [10].…”