Causes and consequences of individual variation in animal movement

Abstract

Animal movement comes in a variety of ‘types’ including small foraging movements, larger one-way dispersive movements, seasonally-predictable round-trip migratory movements, and erratic nomadic movements. Although most individuals move at some point throughout their lives, movement patterns can vary widely across individuals within the same species: differing within an individual over time (intra-individual), among individuals in the same population (inter-individual), or among populations (inter-population). Yet, studies of movement (theoretical and empirical alike) more often focus on understanding ‘typical’ movement patterns than understanding variation in movement. Here, I synthesize current knowledge of movement variation (drawing parallels across species and movement types), describing the causes (what factors contribute to individual variation), patterns (what movement variation looks like), consequences (why variation matters), maintenance (why variation persists), implications (for management and conservation), and finally gaps (what pieces we are currently missing). By synthesizing across scales of variation, I span across work on plasticity, personality, and geographic variation. Individual movement can be driven by factors that act at the individual, population, community and ecosystem level and have ramifications at each of these levels. Generally the consequences of movement are less well understood than the causes, in part because the effects of movement variation are often nested, with variation manifesting at the population level, which in turn affects communities and ecosystems. Understanding both cause and consequence is particularly important for predicting when variation begets variation in a positive feedback loop, versus when a negative feedback causes variation to be dampened successively. Finally, maintaining standing variation in movement may be important for facilitating species’ ability to respond to future environmental change.

A guide for studying among-individual behavioral variation from movement data in the wild

“…life stage, sex, age, the social or non-social environment or reversible internal states (reviewed in 1). Yet, among-individual differences in movement behavior beyond such effects are common [1,52]. We here review the evidence for among-individual variation in movement patterns within populations spanning movement of avian, aquatic, and terrestrial taxa.…”

“…Identifying the causes of individual variation in movement has been a key topic in movement ecology over the past decades [1]. Apart from variation due to life stage or sex, movement ecologists often examine individual variation in movement caused by external factors such as differences in the social and non-social environment, or variation in internal state such as hunger level or motivation to find a mating partner [2].…”

Urban specialization reduces habitat connectivity by a highly mobile wading bird

“…In many cases, movement is assumed to be optimal and equivalent across all individuals [29] (but see [30]). However, individuals often differ in their movement patterns [31,32], which can complicate estimates of functional connectivity. For example, individuals can specialize in their use of habitat types (e.g., "urban" and "nonurban" individuals) [33,34], especially in circumstances where urban habitats favor specific behavioral types [13].…”

Going underground: short- and long-term movements may reveal the fossorial spatial ecology of an amphisbaenian

“…These factors determine that some species or classes of individuals are more territorial or sedentary, showing high site fidelity to a small area, while others behave as floaters or nomadic, and move widely around large areas [ 10 – 12 ]. Furthermore, within the same species, these variations are often associated with sexual or ontogenetic differences [ 10 – 12 ]; for example, males move more often and have larger territories to search and have access to more females, whereas females’ home ranges are generally smaller because they primarily depend on food resources [ 5 ]. Also juveniles may be more nomadic, dispersing over large areas before they settle as adults in a given territory [ 9 , 13 ].…”