Experimental evidence for inherent Lévy search behaviour in foraging animals

Abstract

Recently, Lévy walks have been put forward as a new paradigm for animal search and many cases have been made for its presence in nature. However, it remains debated whether Lévy walks are an inherent behavioural strategy or emerge from the animal reacting to its habitat. Here, we demonstrate signatures of Lévy behaviour in the search movement of mud snails (Hydrobia ulvae) based on a novel, direct assessment of movement properties in an experimental set-up using different food distributions. Our experimental data uncovered clusters of small movement steps alternating with long moves independent of food encounter and landscape complexity. Moreover, size distributions of these clusters followed truncated power laws. These two findings are characteristic signatures of mechanisms underlying inherent Lévy-like movement. Thus, our study provides clear experimental evidence that such multi-scale movement is an inherent behaviour rather than resulting from the animal interacting with its environment.

Intrinsic Lévy behaviour in organisms – searching for a mechanism

“…However, this explanation is not outwith the LFF hypothesis in my view. In addition to it being possible for scalefree activities to be generated intrinsically [13,15,16], it is also possible that an innate, intrinsic pattern is flexible, is under selection and becomes 'optimal' in the general environment in which a species finds itself. For example, the nematode worm (Caenorhabditis elegans) undertakes searching movements for food that show behavioural transition between an environmentally informed 'extrinsic' strategy that is influenced by recent experience and controls area-restricted searching, and a time-dependent 'intrinsic' strategy that reduces spatial oversampling and improves random encounter success [21].…”

“…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.…”

The “Lévy or Diffusion” Controversy: How Important Is the Movement Pattern in the Context of Trapping?

“…A large number of studies has shown that animal movement can follow a more complicated movement pattern where the step distribution decays much more slowly according to some type of inverse power law (heavy or fat tail), known as Lévy walks [32,45,70]. As a result, individuals have a greater chance of executing 'rare' large steps, and therefore, the properties of the random walk are altered.…”

The “Lévy or Diffusion” Controversy: How Important is the Movement Pattern in the Context of Trapping?

“…A large number of studies have shown that animal movement can follow a more complicated movement pattern where the step distribution decays much slower according to some type of inverse power law (heavy or fat tail), known as Lévy walks [32,44,69]. As a result, individuals have a greater chance of executing 'rare' large steps, and therefore the properties of the random walk are altered.…”