Movement is important to all organisms, and accordingly it is addressed in a huge number of papers in the literature. Of nearly 26,000 papers referring to movement, an estimated 34% focused on movement by measuring it or testing hypotheses about it. This enormous amount of information is difficult to review and highlights the need to assess the collective completeness of movement studies and identify gaps. We surveyed 1,000 randomly selected papers from 496 journals and compared the facets of movement studied with a suggested framework for movement ecology, consisting of internal state (motivation, physiology), motion and navigation capacities, and external factors (both the physical environment and living organisms), and links among these components.
Explanation: Most studies simply measured and described the movement of organisms without reference to ecological or internal factors, and the most frequently studied part of the framework was the link between external factors and motion capacity. Few studies looked at the effects on movement of navigation capacity, or internal state, and those were mainly from vertebrates. For invertebrates and plants most studies were at the population level, whereas more vertebrate studies were conducted at the individual level. Consideration of only population-level averages promulgates neglect of between-individual variation in movement, potentially hindering the study of factors controlling movement. Terminology was found to be inconsistent among taxa and subdisciplines. The gaps identified in coverage of movement studies highlight research areas that should be addressed to fully understand the ecology of movement.
Keywords: dispersal, foraging, migration, navigation, physiology
Almost all organisms have to move at some point during their lives, either under their own locomotion or transported by physical processes or organic agents. Movement is beguiling in its variety and complexity. For example, why do sooty shearwaters with chicks in nests in New Zealand regularly forage in the waters off California or Alaska ( 1 )? Why do some planktonic organisms undergo regular daily vertical migrations ( 2 )? Why do some species show nomadic movements, and others follow fixed-route roundtrip migrations ( 3 )? Movement is often in response to short-term goals such as reproduction, maintenance, including feeding, and survival, including escaping threats. It may also be shaped by longer-term fitness implications, such as avoidance of inbreeding and population extinction. Its importance in biology is attested to by numerous books (e.g., ref. 3 ).
Here, we address the movement of whole organisms or gametes as opposed to the movement of appendages, molecules, or physical entities. Terminology for movement is, at best, confusing. Some terms such as “movement” are frequently used for body parts rather than whole organisms, and others such as “orientation” have multiple meanings, some of which are relevant to movement and others not (e.g., policy orientation, or compass direction). Physical entities, such as water, sediments, or tectonic plates, also move.
