Animal locomotion 1132756 220366469 2008-06-19T14:44:50Z PoisonedQuill 1994215 /* Flight */ fixed typo [[Image:Beeinflightfromfront.jpg|thumb|right|A [[bee]] in flight.]] In [[biomechanics]], '''animal locomotion''' is the study of how [[animal]]s [[motion (physics)|move]]. Not all animals move, but locomotive ability is widespread throughout the animal kingdom. As all animals are [[heterotroph]]s, they must obtain food from their environment. Some animals such as [[sponge]]s are [[sessile]], and move the fluid in which they live through their body (this is known as [[filter feeding]]). However, most animals must move around to find food, a mate, and so forth. Ability to do so efficiently is therefore essential to their survival. Locomotion requires [[energy]] to overcome [[friction]] and often [[gravity]] as well. In [[Terrestrial planet|terrestrial]] environments gravity must be overcome, though the friction of air is much less of an issue (except for [[crawling]] animals like worms, for which friction is much higher). In aqueous environments however, friction (or drag) becomes the major challenge, with gravity being less of a concern. Although animals with natural [[buoyancy]] need not expend much energy maintaining vertical position, though some will naturally sink and must expend energy to remain afloat. Friction may also present a problem in [[flight]], and the [[aerodynamic]]ally efficient body shapes of [[bird]]s highlight this point. Flight presents a different problem from movement in water however, as there is no way for a living organism to have lower [[density]] than air. Much of the study is an application of [[Newton's laws of motion|Newton's third law of motion]]: if at rest, to move forwards an animal must push something backwards. Terrestrial animals must push the solid ground, swimming and flying animals must push against a [[fluid]] or [[gas]] (either [[water]] or [[air]]). <ref> {{Citation | title=Constructing Animal Locomotion from New Thermodynamics Theory | first1=Adrian | last1=Bejan | first2=James H. | last2=Marden | journal=American Scientist | volume=94 | issue=4 | year=2006 | pages=pp. 342-349}} </ref> ==Classification== Animals move through a variety of fluids, such as water, air and mud. Some may move through more than one, such [[Pinniped|seal]]s and [[otter]]s. In some cases locomotion is facilitated by the substrate on which they move. Forms of locomotion include: <!-- Need to merge this into the section * [[animal locomotion in water]] ([[swimming]] including [[fish locomotion|fish]] and [[duck]]s, most terrestrial animals also have the [[ability to swim]]) * [[animal locomotion through the ground]] ('swimming' in sand or mud, or [[burrowing]]) * [[climbing animals|animal locomotion on steep, vertical, and overhanging surfaces]] ([[climbing]] on [[tree]]s or on rockfaces - for example, [[lemur]]s in trees, [[mountain goat]]s on a cliff face, or [[flies]] or [[gecko]]s on the ceiling) --> ===Through a fluid medium=== ====Swimming==== [[Image:Octopus vulgaris2.jpg|thumb|right|The [[Common Octopus]] (''Octopus vulgaris'') uses jet-propulsion to move through the water.]] In the water staying afloat is possible through buoyancy. Provided an aquatic animal's body is no denser than its aqueous environment, it should be able to stay afloat well enough. Though this means little energy need be expended maintaining vertical position, it makes movement in the horizontal plane much more difficult. The [[Drag (physics)|drag]] encountered in water is much higher than that of air, which is almost negligible at low speeds. Body shape is therefore important for efficient movement, which is essential for basic functions like [[predation|catching prey]]. A fusiform, [[torpedo]]-like body form is seen in many marine animals, though the mechanisms they employ for movement are diverse. Movement of the body may be from side to side, as in [[shark]]s and many [[fish]]es, or up and down, as in [[marine mammal]]s. Other animals, such as those from the class ''[[Cephalopoda]]'', use jet-propulsion, taking in water then squirting it back out in an explosive burst. Others may rely predominantly on their limbs, much as humans do when swimming. Though life on land originated from the seas, terrestrial animals have returned to an aquatic lifestyle on several occasions, such as the fully aquatic [[cetacean]]s, now far removed from their terrestrial ancestors. ====Flight==== [[Image:Pelicano volando.jpg|thumb|right|Pelican in flight]] {{Main|Flying and gliding animals}} Gravity is a major problem for flight through the air. Because it is impossible for any organism to approach the density of air, flying animals must generate enough [[Lift (soaring)|lift]] to ascend and remain airborne. Wing shape is crucial in achieving this, generating a pressure gradient that results in an upward force on the animal' body. The same principle applies to [[airplane]]s, the wings of which are also [[airfoil]]s. Unlike aircraft however, flying animals must be very light to achieve flight, the largest birds being around 20 kilograms.<ref name=Campbell>{{cite book | last = Campbell | first = Neil A. | coauthors = Reece, Jane B. | title = Biology | publisher = Benjamin Cummings | date = 2005 | id = ISBN 0-8053-7146-X }}</ref> Other structural modifications of flying animals include reduced and redistributed body weight, fusiform shape and powerful flight muscles. Rather than fly, some animals simply reduce their rate of falling by gliding. Flight has [[convergent evolution|independently]] evolved at least four times, in the [[insect flight|insect]]s, [[pterosaur]]s, [[bird flight|bird]]s, and [[bat]]s. Gliding has evolved on many more occasions. The advantage gliding provides to [[arboreal]] animals provides a bridge for the [[evolution of flight]]. ===On a substrate=== ====Terrestrial==== {{Main|Terrestrial locomotion}} [[Image:Katta (Lemur catta) jumping.jpg|left|thumb|The [[Ring-tailed Lemur]] jumping.]] Forms of locomotion on land include walking, running, hopping or [[jumping]], and crawling or slithering. Here friction and buoyancy are not longer an issue, but a strong [[skeletal]] and [[muscular]] framework are required in most terrestrial animals for structural support. Each step also requires much energy to overcome [[inertia]], and animals can store [[elastic potential energy]] in their [[tendon]]s to help overcome this. [[Equilibrioception|Balance]] is also required for movement on land. Human [[infant]]s learn to [[crawling|crawl]] first before they are able to stand on two feet, which requires good coordination as well as physical development. Humans are [[bipedal]] animals, standing on two feet and keeping one on the ground at all times while [[walking]]. When [[running]], only one foot is on the ground at any one time at most, and both leave the ground briefly. At higher speeds [[momentum]] helps keep the body upright, so more energy can be used in movement. The number of legs an animal has varies greatly, resulting in differences in locomotion. Many familiar mammals have four legs; insects have six, while [[spider]]s have eight. Centipedes and millipedes have many sets of legs. Some have none at all, relying on other modes of locomotion. Animals that crawl or slither must use more energy due to the higher friction levels. [[Earthworm]]s crawl by a [[peristalsis]], the same rhythmic contractions that propel food through the digestive tract. [[Snake]]s move differently, undulating from side to side or lifting and repositioning their [[scale (zoology)|scale]]s. Some animals are specialized for moving on non-horizontal surfaces. One common habitat for such [[climbing animals]] is in trees, for example the [[gibbon]] is specialized for [[arboreal]] movement , traveling rapidly by [[brachiation]]. Another case is animals like the [[snow leopard]] living on steep rock faces such as are found in [[mountain]]s. Some light animals are able to climb up smooth sheer surfaces or hang upside down by [[adhesion]]. Many insects can do this, though much larger animals such as [[gecko]]s can also perform similar feats. ====On water==== {{Main|Animal locomotion on the surface layer of water}} While animals like ducks can swim in water by floating, some small animals move across it without breaking through the surface. This surface locomotion takes advantage of the [[surface tension]] of water. Animals that move in such a way include the [[water strider]]. Water striders have legs that are [[hydrophobic]], preventing them from interfering with the structure of water. Another form of locomotion (in which the surface layer is broken) is used by the [[Basilisk lizard]]. ==Energetics== [[Image:Periophthalmus gracilis.jpg|right|thumb|[[Mudskipper]]s move in both terrestrial and aquatic environments, and their body form highlights the trade-off between the two.]] The [[Bioenergetics#Bioenergetics|energetics]] of locomotion involves the energy expenditure by animals in moving. Animals that swim expend less energy per unit of body mass per meter traveled. Flying animals expend more, however running terrestrial animals actually expend more energy for the distance traveled than those that fly. Flying animals use the most energy per unit time, however.<ref name="Campbell">{{cite book | last = Campbell | first = Neil A. | coauthors = Reece, Jane B. | title = Biology, 7th Edition | publisher = Pearson - Benjamin Cummings | date = 2005 | location = San Francisco | pages = 522-523 | isbn = 0-8053-7171-0}}</ref> This does not mean that an animal that normally moves by running would be a more efficient swimmer, however; these comparisons assume an animal is specialized for that form of motion. Another consideration here is [[body mass]]&mdash;heavier animals, though using more total energy, require less energy ''per unit mass'' to move. [[Physiology|Physiologists]] generally measure energy use by the amount of [[oxygen]] consumed, or the amount of [[carbon dioxide]] produced, in an animal's [[respiration (physiology)|respiration]].<ref name="Campbell" /> Energy consumed in locomotion is not available for other efforts, so animals have evolved to be highly efficient in movement. Having said that, some animals move through different environments, such as the mudskipper pictured above, so their movement will be below optimum for any given environment. In this case the optimum reached is a trade-off between the different forms of locomotion. ==See also== *[[Feather]] *[[Joint]] *[[Kinesis]] *[[Taxis]] ==References== {{Commons|Animal locomotion}} <references /> ==Further reading== *McNeill Alexander, Robert. (2003) ''Principles of Animal Locomotion''. Princeton University Press, Princeton, N.J. ISBN 0691086788 == External links == * [http://www.dukenews.duke.edu/2005/12/locomotiontheory.html Unified Physics Theory Explains Animals' Running, Flying And Swimming] [[Category:Locomotion]] [[Category:Zoology]] [[bg:Локомоция]] [[ca:Locomoció animal]] [[hu:Állatok mozgása]] [[mk:Систем за движење]] [[ru:Локомоция]]