title: Apparent power-law distributions in animal movements can arise from intraspecific interactions.
abstract: Lévy flights have gained prominence for analysis of animal movement. In a Lévy flight, step-lengths are drawn from a heavy-tailed distribution such as a power law (PL), and a large number of empirical demonstrations have been published. Others, however, have suggested that animal movement is ill fit by PL distributions or contend a state-switching process better explains apparent Lévy flight movement patterns. We used a mix of direct behavioural observations and GPS tracking to understand step-length patterns in females of two related butterflies. We initially found movement in one species (Euphydryas editha taylori) was best fit by a bounded PL, evidence of a Lévy flight, while the other (Euphydryas phaeton) was best fit by an exponential distribution. Subsequent analyses introduced additional candidate models and used behavioural observations to sort steps based on intraspecific interactions (interactions were rare in E. phaeton but common in E. e. taylori). These analyses showed a mixed-exponential is favoured over the bounded PL for E. e. taylori and that when step-lengths were sorted into states based on the influence of harassing conspecific males, both states were best fit by simple exponential distributions. The direct behavioural observations allowed us to infer the underlying behavioural mechanism is a state-switching process driven by intraspecific interactions rather than a Lévy flight.
authors.affiliation: Department of Biological Sciences, University of Alberta, Edmonton, Canada AB T6G 2E9 gabreed@alaska.edu.
authors.forename: Greg A
authors.initials: GA
authors.lastname: Breed
authors.affiliation: Department of Botany and Plant Pathology, Oregon State University, 2082 Cordley Hall, Corvallis, OR, USA.
authors.forename: Paul M
authors.initials: PM
authors.lastname: Severns
authors.affiliation: Marine Ecosystems and Aquaculture Division, Pacific Biological Station, Fisheries and Oceans Canada, 3190 Hammond Bay Road, Nanaimo, British Columbia, Canada V9T 6N7.
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Edwards
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000502:physiology*; D002080:Butterflies / Q000502:physiology*; D005260:Female; D008124:Locomotion / Q000502:physiology*; D008297:Male; D008954:Models, Biological
keywords: Lévy flight; animal movement; animal movement models; correlated random walk; diffusion; optimal search