From single steps to mass migration: the problem of scale in the movement ecology of the Serengeti wildebeest

Abstract

A central question in ecology is how to link processes that occur over different scales. The daily interactions of individual organisms ultimately determine community dynamics, population fluctuations and the functioning of entire ecosystems. Observations of these multiscale ecological processes are constrained by various technological, biological or logistical issues, and there are often vast discrepancies between the scale at which observation is possible and the scale of the question of interest. Animal movement is characterized by processes that act over multiple spatial and temporal scales. Second-by-second decisions accumulate to produce annual movement patterns. Individuals influence, and are influenced by, collective movement decisions, which then govern the spatial distribution of populations and the connectivity of meta-populations. While the field of movement ecology is experiencing unprecedented growth in the availability of movement data, there remain challenges in integrating observations with questions of ecological interest. In this article, we present the major challenges of addressing these issues within the context of the Serengeti wildebeest migration, a keystone ecological phenomena that crosses multiple scales of space, time and biological complexity.This article is part of the theme issue 'Collective movement ecology'.

Challenges and solutions for studying collective animal behaviour in the wild

“…While UAVs offer unparalleled affordability, flexibility and resolution for imaging animal groups from an aerial perspective, there have been notable advances in satellite remote sensing technology that will facilitate truly 'landscape-scale' studies of collective behaviour in the very near future [49]. Commercial satellite companies maintain the largest collection of archived images with the resolution appropriate for identifying individual animals (30 cm [50] to 50 cm [50,51]), but the random and disparate temporal distribution of coverage generally limits the use of archived images for studies of collective movement.…”

Male-Biased Partial Migration in a Giraffe Population

“…Additionally, few studies account for variation in movement strategies across different age and sex classes because of logistical constraints associated with collaring multiple individuals across these different categories. Because of these limitations, studies connecting varying movement behaviors among different age/sex classes to population level processes over longer time periods are rare and as result, researchers lack the ability to evaluate causes and consequences of movement across multiple scales (Torney et al, 2018). This shortage of empirical inquiry limits the understanding of the associations among varying movement strategies, population dynamics and landscape-level processes and can potentially result in misinformed conservation strategies that do not properly account for the demographic effects of movement processes over larger timescales (Bolger et al, 2008).…”

A Langevin dynamics approach to the distribution of animal move lengths

“…However, it is important to make clear that superdiffusive behavior in realistic animal movement has an ecological scale limit. In fact, identifying the ecological range of scales where superdiffusive regimes emerge can help to understand relevant components of animal ecology [27]. In this sense, as the second moment of P ( ) is finite in animal movement behavior, superdiffusive Lévy-like dynamics cannot extend indefinitely since, according to the CLT, the convergence to the normal (Gaussian) dynamics eventually takes place, even if it occurs only rather slowly [52].…”

“…We are able to generate most of the relevant move length distributions P ( ) that have been usually considered in the literature of movement ecology. Diffusive and Lévy-like superdiffusive movement dynamics [5,6] emerge naturally in this context, as well as the possibility of multiscale movement behavior [27,28].…”