Swarm behaviour, or
swarming, is a collective behaviour exhibited by animals of similar size which aggregate together, perhaps milling about the same spot or perhaps moving
en masse or
migratingAnimal migration is the relatively long-distance movement of individuals, usually on a seasonal basis. It is a ubiquitous phenomenon, found in all major animal groups, including birds, mammals, fish, reptiles, amphibians, insects, and crustaceans. The trigger for the migration may be local...
in some direction. As a term,
swarming is applied particularly to insects, but can also be applied to any other animal that exhibits swarm behaviour. The term
flocking is usually used to refer specifically to swarm behaviour in birds,
herding to refer to swarm behaviour in quadrupeds,
shoaling or schoolingIn biology, any group of fish that stay together for social reasons are said to be shoaling , and if, in addition, the group is swimming in the same direction in a coordinated manner, they are said to be schooling . In common usage, the terms are sometimes used rather loosely...
to refer to swarm behaviour in fish.
PhytoplanktonPhytoplankton are the autotrophic component of the plankton community. The name comes from the Greek words φυτόν , meaning "plant", and πλαγκτός , meaning "wanderer" or "drifter". Most phytoplankton are too small to be individually seen with the unaided eye...
also gather in huge swarms called
bloomsAn algal bloom is a rapid increase or accumulation in the population of algae in an aquatic system. Algal blooms may occur in freshwater as well as marine environments. Typically, only one or a small number of phytoplankton species are involved, and some blooms may be recognized by discoloration...
, although these organisms are
algaeAlgae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...
and are not self propelled the way animals are. By extension, the term swarm is applied also to inanimate entities which exhibit parallel behaviours, as in a
robot swarmSwarm robotics is a new approach to the coordination of multirobot systems which consist of large numbers of mostly simple physical robots. It is supposed that a desired collective behavior emerges from the interactions between the robots and interactions of robots with the environment...
, an
earthquake swarmEarthquake swarms are events where a local area experiences sequences of many earthquakes striking in a relatively short period of time. The length of time used to define the swarm itself varies, but the United States Geological Survey points out that an event may be on the order of days, weeks, or...
, or a swarm of stars.
From a more abstract point of view, swarm behaviour is the collective motion of a large number of self-propelled entities. From the perspective of the mathematical modeller, it is an
emergentIn philosophy, systems theory, science, and art, emergence is the way complex systems and patterns arise out of a multiplicity of relatively simple interactions. Emergence is central to the theories of integrative levels and of complex systems....
behaviour arising from simple rules that are followed by individuals and does not involve any central coordination.
Swarm behaviour was first simulated on a computer in 1986 with the simulation program
boidsBoids is an artificial life program, developed by Craig Reynolds in 1986, which simulates the flocking behaviour of birds. His paper on this topic was published in 1987 in the proceedings of the ACM SIGGRAPH conference...
. This program simulates simple
agentsAgent-based models have many applications in biology, primarily due to the characteristics of the modeling method. Agent-based modeling is a rule-based, computational modeling methodology that focuses on rules and interactions among the individual components or the agents of the system...
(boids) that are allowed to move according to a set of basic rules. The model was originally designed to mimic the flocking behaviour of birds, but it can be applied also to schooling fish and other swarming entities.
Models
The simplest mathematical models of animal swarms generally represent individual animals as following three rules:
- Move in the same direction as your neighbours
- Remain close to your neighbours
- Avoid collisions with your neighbours
The
boidsBoids is an artificial life program, developed by Craig Reynolds in 1986, which simulates the flocking behaviour of birds. His paper on this topic was published in 1987 in the proceedings of the ACM SIGGRAPH conference...
computer program, created by
Craig ReynoldsCraig W. Reynolds , is an artificial life and computer graphics expert, who created the Boids artificial life simulation in 1986. Reynolds worked on the film Tron as a scene programmer, and on Batman Returns as part of the video image crew. He is the author of the OpenSteer library.-External...
in 1986, simulates swarm behaviour following the above rules. Many subsequent and current models use variations on these rules, often implementing them by means of concentric "zones" around each animal. In the
zone of repulsion, very close to the animal, the focal animal will seek to distance itself from its neighbours to avoid collision. Slightly further away, in the
zone of alignment, the focal animal will seek to align its direction of motion with its neighbours. In the outermost
zone of attraction, which extends as far away from the focal animal as it is able to sense, the focal animal will seek to move towards a neighbour.
The shape of these zones will necessarily be affected by the sensory capabilities of the given animal. For example the visual field of a bird does not extend behind its body. Fish rely on both vision and on hydrodynamic perceptions relayed through their
lateral lineThe lateral line is a sense organ in aquatic organisms , used to detect movement and vibration in the surrounding water. Lateral lines are usually visible as faint lines running lengthwise down each side, from the vicinity of the gill covers to the base of the tail...
, while Antarctic
krillKrill is the common name given to the order Euphausiacea of shrimp-like marine crustaceans. Also known as euphausiids, these small invertebrates are found in all oceans of the world...
rely both on vision and hydrodynamic signals relayed through
antennaeAntennae in biology have historically been paired appendages used for sensing in arthropods. More recently, the term has also been applied to cilium structures present in most cell types of eukaryotes....
.
However recent studies of starling flocks have shown that each bird modifies its position, relative to the six or seven animals directly surrounding it, no matter how close or how far away those animals are. Interactions between flocking starlings are thus based on a topological rule rather than a metric rule. It remains to be seen whether this applies to other animals.
Agents
Self-organization
Swarm intelligence
Swarm intelligenceSwarm intelligence is the collective behaviour of decentralized, self-organized systems, natural or artificial. The concept is employed in work on artificial intelligence...
is the collective behaviour of
decentralized__FORCETOC__Decentralization or decentralisation is the process of dispersing decision-making governance closer to the people and/or citizens. It includes the dispersal of administration or governance in sectors or areas like engineering, management science, political science, political economy,...
, self-organized systems, natural or artificial. The concept is employed in work on
artificial intelligenceArtificial intelligence is the intelligence of machines and the branch of computer science that aims to create it. AI textbooks define the field as "the study and design of intelligent agents" where an intelligent agent is a system that perceives its environment and takes actions that maximize its...
. The expression was introduced by
Gerardo BeniGerardo Beni is a professor of electrical engineering at University of California, Riverside who, with Jin Wang, is known as the originator of the term 'swarm intelligence' in the context of cellular robotics and the concept of 'electrowetting' , with Susan Hackwood...
and Jing Wang in 1989, in the context of
cellular roboticA cellular automaton is a discrete model studied in computability theory, mathematics, physics, complexity science, theoretical biology and microstructure modeling. It consists of a regular grid of cells, each in one of a finite number of states, such as "On" and "Off"...
systems.
Swarm intelligence systems are typically made up of a population of simple
agentsAgent-based models have many applications in biology, primarily due to the characteristics of the modeling method. Agent-based modeling is a rule-based, computational modeling methodology that focuses on rules and interactions among the individual components or the agents of the system...
or
boidsBoids is an artificial life program, developed by Craig Reynolds in 1986, which simulates the flocking behaviour of birds. His paper on this topic was published in 1987 in the proceedings of the ACM SIGGRAPH conference...
interacting locally with one another and with their environment. The agents follow very simple rules, and although there is no centralized control structure dictating how individual agents should behave, local, and to a certain degree random, interactions between such agents lead to the
emergenceIn philosophy, systems theory, science, and art, emergence is the way complex systems and patterns arise out of a multiplicity of relatively simple interactions. Emergence is central to the theories of integrative levels and of complex systems....
of intelligent global behaviour, unknown to the individual agents.
Swarm intelligence research is multidisciplinary. It can be divided into natural swarm research studying biological systems and artificial swarm research studying human artefacts. There is also a scientific stream attempting to model the swarm systems themselves and understand their underlying mechanisms, and an engineering stream focused on applying the insights developed by the scientific stream to solve practical problems in other areas.
Emergence
The concept of emergence—that the properties and functions found at a hierarchical level are not present and are irrelevant at the lower levels–is often a basic principle behind
self-organizing systemsSelf-organization is the process where a structure or pattern appears in a system without a central authority or external element imposing it through planning...
. An example of self-organization in biology leading to emergence in the natural world occurs in ant colonies. The queen does not give direct orders and does not tell the ants what to do. Instead, each ant reacts to stimuli in the form of chemical scent from larvae, other ants, intruders, food and build up of waste, and leaves behind a chemical trail, which, in turn, provides a stimulus to other ants. Here each ant is an autonomous unit that reacts depending only on its local environment and the genetically encoded rules for its variety of ant. Despite the lack of centralized decision making, ant colonies exhibit complex behaviour and have even been able to demonstrate the ability to solve geometric problems. For example, colonies routinely find the maximum distance from all colony entrances to dispose of dead bodies.
Stigmergy
A further key concept in the field of swarm intelligence is
stigmergyStigmergy is a mechanism of indirect coordination between agents or actions. The principle is that the trace left in the environment by an action stimulates the performance of a next action, by the same or a different agent...
. Stigmergy is a mechanism of indirect coordination between agents or actions. The principle is that the trace left in the environment by an action stimulates the performance of a next action, by the same or a different agent. In that way, subsequent actions tend to reinforce and build on each other, leading to the spontaneous emergence of coherent, apparently systematic activity. Stigmergy is a form of self-organization. It produces complex, seemingly intelligent structures, without need for any planning, control, or even direct communication between the agents. As such it supports efficient collaboration between extremely simple agents, who lack any memory, intelligence or even awareness of each other.
Algorithms
Swarm algorithms follow a
LagrangianThe Lagrangian, L, of a dynamical system is a function that summarizes the dynamics of the system. It is named after Joseph Louis Lagrange. The concept of a Lagrangian was originally introduced in a reformulation of classical mechanics by Irish mathematician William Rowan Hamilton known as...
approach or an Eulerian approach. The Eulerian approach views the swarm as a
fieldIn physics, a field is a physical quantity associated with each point of spacetime. A field can be classified as a scalar field, a vector field, a spinor field, or a tensor field according to whether the value of the field at each point is a scalar, a vector, a spinor or, more generally, a tensor,...
, working with the density of the swarm and deriving mean field properties. It is a hydrodynamic approach, and can be useful for modelling the overall dynamics of large swarms. However, most models work with the Lagrangian approach, which is an agent-based model following the individual agents (points or particles) that make up the swarm. Individual particle models can follow information on heading and spacing that is lost in the Eulerian approach.
Ant colony optimization
Ant colony optimizationIn computer science and operations research, the ant colony optimization algorithm ' is a probabilistic technique for solving computational problems which can be reduced to finding good paths through graphs....
is a widely used algorithm which was inspired by the behaviours of ants, and has been effective solving
discrete optimizationDiscrete optimization is a branch of optimization in applied mathematics and computer science.As opposed to continuous optimization, the variables used in the mathematical program are restricted to assume only discrete values, such as the integers.Two notable branches of discrete optimization...
problems related to swarming. The algorithm was initially proposed by
Marco DorigoMarco Dorigo is a research director for the Belgian Funds for Scientific Research , a professor in the computer science department of the University of Paderborn and a co-director of , the artificial intelligence lab of the Université Libre de Bruxelles.He is the proponent of the "ant colony...
in 1992, and has since been diversified to solve a wider class of numerical problems. Species that have multiple queens may have a queen leaving the nest along with some workers to found a colony at a new site, a process akin to swarming in honeybees.
- Ants are behaviourally unsophisticated; collectively they perform complex tasks. Ants have highly developed sophisticated sign-based communication.
- Ants communicate using pheromones; trails are laid that can be followed by other ants.
- Routing problem ants drop different pheromones used to compute the "shortest" path from source to destination(s).
- Rauch EM, Millonas MM and Chialvo DR (1995) "Pattern formation and functionality in swarm models"] Physics Letters A, 207: 185.
Self-propelled particles
Self-propelled particlesSelf-propelled particles , also referred to as self-driven particles or as the Couzin–Vicsek algorithm, is a concept used to model swarm behaviour. The concept was introduced in 1995 by Vicsek and Couzin et al. as a special case of the Boids model introduced in 1986 by Reynolds...
(SPP) is a concept introduced in 1995 by Vicsek and Couzin et al as a special case of the boids model introduced in 1986 by Reynolds. A swarm is modelled in SPP by a collection of particles that move with a constant speed but respond to a random perturbation by adopting at each time increment the average direction of motion of the other particles in their local neighbourhood.
Simulations demonstrate that a suitable "nearest neighbour rule" eventually results in all the particles swarming together, or moving in the same direction. This emerges, even though there is no centralized coordination, and even though the neighbours for each particle constantly change over time (see the interactive simulation in the box on the right). SPP models predict that swarming animals share certain properties at the group level, regardless of the type of animals in the swarm. Swarming systems give rise to emergent behaviours which occur at many different scales, some of which are turning out to be both universal and robust. It has become a challenge in theoretical physics to find minimal statistical models that capture these behaviours.
Particle swarm optimization
Particle swarm optimizationIn computer science, particle swarm optimization is a computational method that optimizes a problem by iteratively trying to improve a candidate solution with regard to a given measure of quality...
is another algorithm widely used to solve problems related to swarms. It was developed in 1995 by
KennedyJames Kennedy is an American social psychologist, best known as an originator and researcher of particle swarm optimization. The first papers on the topic, by Kennedy and Russell C. Eberhart, were presented in 1995; since then more than ten thousand papers have been published on particle swarms...
and
EberhartRussell C. Eberhart, an American electrical engineer, best known as the co-developer of particle swarm optimization concept . He is professor of Electrical and Computer Engineering, and adjunct professor of Biomedical Engineering at the Purdue School of Engineering and Technology, Indiana...
and was first aimed at
simulatingA computer simulation, a computer model, or a computational model is a computer program, or network of computers, that attempts to simulate an abstract model of a particular system...
the social behaviour and choreography of bird flocks and fish schools. The algorithm was simplified and it was observed to be performing optimization. The system initially seeds a population with random solutions. It then searches in the
problem spaceIn optimization , a candidate solution is a member of a set of possible solutions to a given problem. A candidate solution does not have to be a likely or reasonable solution to the problem – it is simply in the set that satisfies all constraints.The space of all candidate solutions is called the...
through successive generations using
stochastic optimizationStochastic optimization methods are optimization methods that generate and use random variables. For stochastic problems, the random variables appear in the formulation of the optimization problem itself, which involve random objective functions or random constraints, for example. Stochastic...
to find the best solutions. The solutions it finds are called
particlesA point particle is an idealization of particles heavily used in physics. Its defining feature is that it lacks spatial extension: being zero-dimensional, it does not take up space...
. Each particle stores its position as well as the best solution it has achieved so far. The particle swarm optimizer tracks the
best local valueIn mathematics, the maximum and minimum of a function, known collectively as extrema , are the largest and smallest value that the function takes at a point either within a given neighborhood or on the function domain in its entirety .More generally, the...
obtained so far by any particle in the local neighbourhood. The remaining particles then move through the problem space following the lead of the optimum particles. At each time iteration, the particle swarm optimiser accelerates each particle toward its optimum locations according to simple mathematical rules. Particle swarm optimization has been applied in many areas. It has few parameters to adjust, and a version that works well for a specific applications can also work well with minor modifications across a range of related applications. A book by Kennedy and Eberhart describes some philosophical aspects of particle swarm optimization applications and swarm intelligence. An extensive survey of applications is made by Poli.
Biological swarming
Examples of biological swarming are found in
bird flocksFlocking behavior is the behavior exhibited when a group of birds, called a flock, are foraging or in flight. There are parallels with the shoaling behavior of fish, the swarming behavior of insects, and herd behavior of land animals....
,
fish schoolsIn biology, any group of fish that stay together for social reasons are said to be shoaling , and if, in addition, the group is swimming in the same direction in a coordinated manner, they are said to be schooling . In common usage, the terms are sometimes used rather loosely...
, insect swarms, bacteria swarms, molds, molecular motors,
quadruped herdsHerd refers to a social grouping of certain animals of the same species, either wild or domestic, and also to the form of collective animal behavior associated with this or as a verb, to herd, to its control by another species such as humans or dogs.The term herd is generally applied to mammals,...
and people.
- Swarm Theory National Geographic. Feature article, July 2007.
- Beekman M, Sword GA and Simpson SK (2008) Biological Foundations of Swarm Intelligence. In Swarm intelligence: introduction and applications, Eds Blum C and Merkle D. シュプリンガー・ジャパン株式会社, Page 3–43. ISBN 978-3-540-74088-9
- Spawning
Spawn refers to the eggs and sperm released or deposited, usually into water, by aquatic animals. As a verb, spawn refers to the process of releasing the eggs and sperm, also called spawning...
- Synchronous spawning
- External fertilization
External fertilization is a form of fertilization in which a sperm cell is united with an egg cell external to the bodies of the reproducing individuals. In contrast, internal fertilization takes place inside the female after insemination through copulation....
Insects
The behaviour of insects that live in
coloniesIn biology, a colony reference to several individual organisms of the same species living closely together, usually for mutual benefit, such as stronger defense or the ability to attack bigger prey. Some insects live only in colonies...
, such as ants, bees, wasps and termites, has always been a source of fascination for children, naturalists and artists. Individual insects seems to do their own thing without any central control, yet the colony as a whole behaves in a highly coordinated manner. Researchers have found that cooperation at the colony level is largely
self-organizedSelf-organization is the process where a structure or pattern appears in a system without a central authority or external element imposing it through planning...
. The group coordination that emerges is often just a consequence of the way individuals in the colony interact. These interactions can be remarkably simple, such as one ant merely following the trail left by another ant. Yet put together, the cumulative effect of such behaviours can solve highly complex problems, such as locating the shortest route in a network of possible paths to a food source. The organised behaviour that emerges in this way is sometimes called
swarm intelligenceSwarm intelligence is the collective behaviour of decentralized, self-organized systems, natural or artificial. The concept is employed in work on artificial intelligence...
.
Ants
Individual ants do not exhibit complex behaviours, yet a colony of ants collectively achieves complex tasks such as constructing nests, taking care of their young, building bridges and foraging for food. A colony of ants can locate the food source nearest their nest without any individual ant possessing any knowledge about that. If there are two paths from the ant nest to a food source, then the colony usually selects the shorter path. This is because individual ants lay down chemical trails as they move, a
pheromoneA pheromone is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting outside the body of the secreting individual to impact the behavior of the receiving individual...
which is then followed by other ants. The ants that first return to the nest from the food source are more likely to be those that took the shorter path. More ants then retrace the shorter path, reinforcing the pheromone trail. In this way, "the ants collectively solve an optimization problem using emergent computation."
The successful techniques used by
antAnts are social insects of the family Formicidae and, along with the related wasps and bees, belong to the order Hymenoptera. Ants evolved from wasp-like ancestors in the mid-Cretaceous period between 110 and 130 million years ago and diversified after the rise of flowering plants. More than...
colonies have been studied in computer science and robotics to produce distributed and fault-tolerant systems for solving problems. This area of
biomimeticsBiomimetics is the study of the structure and function of biological systems as models for the design and engineering of materials and machines. It is widely regarded as being synonymous with biomimicry, biomimesis, biognosis and similar to biologically inspired design.-History:The term biomimetics...
has led to studies of ant locomotion, search engines that make use of "foraging trails", fault-tolerant storage and networking algorithms.
Bees
When a honey bee swarm emerges from a hive they do not fly far at first. They may gather in a tree or on a branch only a few meters from the hive. There, they cluster about the queen and send 20 -50 scout bees out to find a suitable new nest locations. The scout bees are the most experienced foragers in the cluster. An individual scout returning to the cluster promotes a location she found. She uses a dance similar to the
waggle danceWaggle dance is a term used in beekeeping and ethology for a particular figure-eight dance of the honey bee. By performing this dance, successful foragers can share with their hive mates information about the direction and distance to patches of flowers yielding nectar and pollen, to water...
to indicate direction and distance to others in the cluster. The more excited she is about her findings the more excitedly she dances. If she can convince other scouts to check out the location she found, they may take off, check out the proposed site and promote the site further upon their return. Several different sites may be promoted by different scouts at first. After several hours and sometimes days, slowly a favourite location emerges from this decision making process. When all scouts agree on a final location the whole cluster takes off and flies to it. A swarm may fly for a kilometre or more to the scouted out location. This collective decision making process is remarkably successful in identifying the most suitable new nest site and keeping the swarm intact. A good nest site has to be large enough to accommodate the swarm (about 15 litres in volume), has to be well protected from the elements, receive a certain amount of warmth from the sun and be not infested with ants.
Cockroaches
Similar to ants,
cockroachCockroaches are insects of the order Blattaria or Blattodea, of which about 30 species out of 4,500 total are associated with human habitations...
es leave chemical trails in their faeces as well as emitting airborne pheromones for swarming and mating. Other cockroaches will follow these trails to discover sources of food and water, and also discover where other cockroaches are hiding. Thus, cockroaches can exhibit emergent behaviour, in which group or swarm behaviour emerges from a simple set of individual interactions.
Cockroaches are mainly nocturnal and will run away when exposed to light. A study tested the hypothesis that cockroaches use just two pieces of information to decide where to go under those conditions: how dark it is and how many other cockroaches there are. The study conducted by José Halloy and colleagues at the
Free University of BrusselsThe Université libre de Bruxelles is a French-speaking university in Brussels, Belgium. It has 21,000 students, 29% of whom come from abroad, and an equally cosmopolitan staff.-Name:...
and other European institutions created a set of tiny
robotA robot is a mechanical or virtual intelligent agent that can perform tasks automatically or with guidance, typically by remote control. In practice a robot is usually an electro-mechanical machine that is guided by computer and electronic programming. Robots can be autonomous, semi-autonomous or...
s that appear to the roaches as other roaches and can thus alter the roaches' perception of
critical massCritical mass is a sociodynamic term to describe the existence of sufficient momentum in a social system such that the momentum becomes self-sustaining and creates further growth....
. The robots were also specially scented so that they would be accepted by the real roaches.
Locusts
Locusts are the swarming phase of the short-horned
grasshopperThe grasshopper is an insect of the suborder Caelifera in the order Orthoptera. To distinguish it from bush crickets or katydids, it is sometimes referred to as the short-horned grasshopper...
s of the family
AcrididaeThe Acrididae are the predominant family of grasshoppers, comprising some 10,000 of the 11,000 species of the entire suborder Caelifera. The Acrididae are best known because all locusts are of the Acrididae. The subfamily Oedipodinae is sometimes classified as a distinct family Oedipodidae in the...
. Some species can breed rapidly under suitable conditions and subsequently become gregarious and migratory. They form bands as
nymphsIn biology, a nymph is the immature form of some invertebrates, particularly insects, which undergoes gradual metamorphosis before reaching its adult stage. Unlike a typical larva, a nymph's overall form already resembles that of the adult. In addition, while a nymph moults it never enters a...
and swarms as adults—both of which can travel great distances, rapidly stripping fields and greatly damaging crops. The largest swarms can cover hundreds of square miles and contain billions of locusts. A locust can eat its own weight (about 2 grams) in plants every day. That means one million locusts can eat about one ton of food each day, and the largest swarms can consume over 100,000
tonneThe tonne, known as the metric ton in the US , often put pleonastically as "metric tonne" to avoid confusion with ton, is a metric system unit of mass equal to 1000 kilograms. The tonne is not an International System of Units unit, but is accepted for use with the SI...
s each day.
Swarming in locusts has been found to be associated with increased levels of
serotoninSerotonin or 5-hydroxytryptamine is a monoamine neurotransmitter. Biochemically derived from tryptophan, serotonin is primarily found in the gastrointestinal tract, platelets, and in the central nervous system of animals including humans...
which causes the locust to change colour, eat much more, become mutually attracted, and breed much more easily. Researchers propose that swarming behaviour is a response to overcrowding and studies have shown that increased tactile stimulation of the hind legs or, in some species, simply encountering other individuals causes an increase in levels of serotonin. The transformation of the locust to the swarming variety can be induced by several contacts per minute over a four-hour period.
An individual locust's response to a loss of alignment in the group appears to increase the randomness of its motion, until an aligned state is again achieved. This noise-induced alignment appears to be an intrinsic characteristic of collective coherent motion.
Insect migration
Insect migration is the seasonal movement of
insectInsects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
s, particularly those by species of dragonflies,
beetleColeoptera is an order of insects commonly called beetles. The word "coleoptera" is from the Greek , koleos, "sheath"; and , pteron, "wing", thus "sheathed wing". Coleoptera contains more species than any other order, constituting almost 25% of all known life-forms...
s, butterflies and
mothA moth is an insect closely related to the butterfly, both being of the order Lepidoptera. Moths form the majority of this order; there are thought to be 150,000 to 250,000 different species of moth , with thousands of species yet to be described...
s. The distance can vary from species to species, but in most cases these movements involve large numbers of individuals. In some cases the individuals that migrate in one direction may not return and the next generation may instead migrate in the opposite direction. This is a significant difference from
bird migrationBird migration is the regular seasonal journey undertaken by many species of birds. Bird movements include those made in response to changes in food availability, habitat or weather. Sometimes, journeys are not termed "true migration" because they are irregular or in only one direction...
.
Monarch butterfliesThe Monarch butterfly is a milkweed butterfly , in the family Nymphalidae. It is perhaps the best known of all North American butterflies. Since the 19th century, it has been found in New Zealand, and in Australia since 1871 where it is called the Wanderer...
are especially noted for their lengthy annual migration. In North America they make massive southward migrations starting in August until the first frost. A northward migration takes place in the spring. The monarch is the only butterfly that migrates both north and south as the birds do on a regular basis. But no single individual makes the entire round trip. Female monarchs deposit eggs for the next generation during these migrations. The length of these journeys exceeds the normal lifespan of most monarchs, which is less than two months for butterflies born in early summer. The last generation of the summer enters into a non-reproductive phase known as
diapauseDiapause is the delay in development in response to regularly and recurring periods of adverse environmental conditions. It is considered to be a physiological state of dormancy with very specific initiating and inhibiting conditions...
and may live seven months or more. During diapause, butterflies fly to one of many overwintering sites. The generation that overwinters generally does not reproduce until it leaves the overwintering site sometime in February and March. It is the second, third and fourth generations that return to their northern locations in the United States and Canada in the spring. How the species manages to return to the same overwintering spots over a gap of several generations is still a subject of research; the flight patterns appear to be inherited, based on a combination of the position of the sun in the sky and a time-compensated Sun compass that depends upon a circadian clock that is based in their antennae.
Birds
Bird migration
Approximately 1800 of world's 10,000 bird species are long-distance migrants. The primary motivation for migration appears to be food; for example, some hummingbirds choose not to migrate if fed through the winter. Also, the longer days of the northern summer provide extended time for
breedingBreeding in the wild is the natural process of animal reproduction occurring in the natural habitat of a given species. This terminology is distinct from animal husbandry or breeding of species in captivity...
birds to feed their young. This helps diurnal birds to produce larger
clutchA clutch of eggs refers to all the eggs produced by birds or reptiles, often at a single time, particularly those laid in a nest.In birds, destruction of a clutch by predators, , results in double-clutching...
es than related non-migratory species that remain in the tropics. As the days shorten in autumn, the birds return to warmer regions where the available food supply varies little with the season. These advantages offset the high stress, physical exertion costs, and other risks of the migration such as predation.
Many, if not most, birds migrate in flocks. For larger birds, flying in flocks reduces energy costs. Geese in a V-formation may conserve 12–20% of the energy they would need to fly alone.
Red knotThe Red Knot, Calidris canutus , is a medium sized shorebird which breeds in tundra and the Arctic Cordillera in the far north of Canada, Europe, and Russia. It is a large member of the Calidris sandpipers, second only to the Great Knot...
s and
dunlinThe Dunlin, Calidris alpina, is a small wader, sometimes separated with the other "stints" in Erolia. It is a circumpolar breeder in Arctic or subarctic regions. Birds that breed in northern Europe and Asia are long-distance migrants, wintering south to Africa, southeast Asia and the Middle East...
s were found in radar studies to fly 5 km per hour faster in flocks than when they were flying alone. Flocks of birds save energy when flying together, much in the way that bicyclists
draftDrafting or slipstreaming is a technique where two vehicles or other moving objects are caused to align in a close group reducing the overall effect of drag due to exploiting the lead object's slipstream...
one another in a
pelotonThe peloton , field, bunch or pack is the large main group of riders in a road bicycle race. Riders in a group save energy by riding close near other riders...
. Geese flying in a Vee formation save energy by flying in the updraft of the
wingtip vortexWingtip vortices are tubes of circulating air that are left behind a wing as it generates lift. One wingtip vortex trails from the tip of each wing. The cores of vortices spin at very high speed and are regions of very low pressure...
generated by the previous animal in the formation. Thus, the birds flying behind do not need to work as hard to achieve lift. Studies show that birds in a V formation place themselves roughly at the optimum distance predicted by simple aerodynamic theory.
The V formation greatly boosts the efficiency and range of flying birds, particularly over long
migratoryBird migration is the regular seasonal journey undertaken by many species of birds. Bird movements include those made in response to changes in food availability, habitat or weather. Sometimes, journeys are not termed "true migration" because they are irregular or in only one direction...
routes. All the birds except the first fly in the upwash from the
wingtip vorticesWingtip vortices are tubes of circulating air that are left behind a wing as it generates lift. One wingtip vortex trails from the tip of each wing. The cores of vortices spin at very high speed and are regions of very low pressure...
of the bird ahead. The upwash assists each bird in supporting its own weight in flight, in the same way a
gliderGlider aircraft are heavier-than-air craft that are supported in flight by the dynamic reaction of the air against their lifting surfaces, and whose free flight does not depend on an engine. Mostly these types of aircraft are intended for routine operation without engines, though engine failure can...
can climb or maintain height indefinitely in rising air. In a V formation of 25 members, each bird can achieve a reduction of induced drag by up to 65% and as a result increase their range by 71%. The birds flying at the tips and at the front are rotated in a timely cyclical fashion to spread flight fatigue equally among the flock members. The formation also makes communication easier and allows the birds to maintain visual contact with each other.
Other animals may use similar drafting techniques when migrating.
LobsterClawed lobsters comprise a family of large marine crustaceans. Highly prized as seafood, lobsters are economically important, and are often one of the most profitable commodities in coastal areas they populate.Though several groups of crustaceans are known as lobsters, the clawed lobsters are most...
s, for example, migrate in close single-file formation "lobster trains", sometimes for hundreds of miles.
Some
bar-tailed godwitThe Bar-tailed Godwit is a large wader in the family Scolopacidae, which breeds on Arctic coasts and tundra mainly in the Old World, and winters on coasts in temperate and tropical regions of the Old World...
s have the longest known non-stop flight of any migrant, flying 11,000 km from
AlaskaAlaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...
to their
New ZealandNew Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
non-breeding areas. Prior to migration, 55 percent of their bodyweight is stored fat to fuel this uninterrupted journey.
The Mediterranean and other seas present a major obstacle to soaring birds, which must cross at the narrowest points. Massive numbers of large
raptorBirds of prey are birds that hunt for food primarily on the wing, using their keen senses, especially vision. They are defined as birds that primarily hunt vertebrates, including other birds. Their talons and beaks tend to be relatively large, powerful and adapted for tearing and/or piercing flesh....
s and storks pass through areas such as
GibraltarGibraltar is a British overseas territory located on the southern end of the Iberian Peninsula at the entrance of the Mediterranean. A peninsula with an area of , it has a northern border with Andalusia, Spain. The Rock of Gibraltar is the major landmark of the region...
,
FalsterboFalsterbo is a town located at the south-western tip of Sweden in Vellinge Municipality in Skåne County. Falsterbo is situated in the southern part of the Falsterbo peninsula. It is part of Skanör med Falsterbo, one of Sweden's historical cities.-History:...
, and the Bosphorus at migration times. More common species, such as the
Honey BuzzardThe European Honey Buzzard , is a bird of prey in the family Accipitridae which also includes many other diurnal raptors such as kites, eagles and harriers....
, can be counted in hundreds of thousands in autumn. Other barriers, such as mountain ranges, can also cause funnelling, particularly of large diurnal migrants. This is a notable factor in the
Central AmericaCentral America is the central geographic region of the Americas. It is the southernmost, isthmian portion of the North American continent, which connects with South America on the southeast. When considered part of the unified continental model, it is considered a subcontinent...
n migratory bottleneck. This concentration of birds during migration can put species at risk. Some spectacular migrants have already gone extinct, the most notable being the
Passenger PigeonThe Passenger Pigeon or Wild Pigeon was a bird, now extinct, that existed in North America and lived in enormous migratory flocks until the early 20th century...
. During migration the flocks were a mile (1.6 km) wide and 300 miles (500 km) long, taking several days to pass and containing up to a billion birds.
Fish
The term "shoal" can be used to describe any group of fish, including mixed-species groups, while "school" is used for more closely knit groups of the same species swimming in a highly synchronised and polarised manner.
Fish derive many benefits from shoaling behaviour including defence against predators (through better predator detection and by diluting the chance of capture), enhanced
foraging- Definitions and significance of foraging behavior :Foraging is the act of searching for and exploiting food resources. It affects an animal's fitness because it plays an important role in an animal's ability to survive and reproduce...
success, and higher success in finding a mate. It is also likely that fish benefit from shoal membership through increased hydrodynamic efficiency.
Fish use many traits to choose shoalmates. Generally they prefer larger shoals, shoalmates of their own species, shoalmates similar in size and appearance to themselves, healthy fish, and kin (when recognised). The "oddity effect" posits that any shoal member that stands out in appearance will be preferentially targeted by predators. This may explain why fish prefer to shoal with individuals that resemble them. The oddity effect would thus tend to homogenise shoals.
One puzzling aspect of shoal selection is how a fish can choose to join a shoal of animals similar to themselves, given that it cannot know its own appearance. Experiments with zebrafish have shown that shoal preference is a learned ability, not innate. A zebrafish tends to associate with shoals that resemble shoals in which it was reared, a form of
imprintingImprinting is the term used in psychology and ethology to describe any kind of phase-sensitive learning that is rapid and apparently independent of the consequences of behavior...
.
Other open questions of shoaling behaviour include identifying which individuals are responsible for the direction of shoal movement. In the case of
migratoryMany types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousands of kilometres...
movement, most members of a shoal seem to know where they are going. In the case of foraging behaviour, captive shoals of
golden shinerThe golden shiner is a cyprinid fish native to eastern North America. It is the sole member of its genus. Much used as a bait fish, it is probably the most widely pond-cultured fish in the United States.-Description:...
(a kind of
minnowMinnow is a general term used to refer to small freshwater and saltwater fish, especially those used as bait fish or for fishing bait. More specifically, it refers to small freshwater fish of the carp family.-True minnows:...
) are led by a small number of experienced individuals who knew when and where food was available.
Radakov estimated herring schools in the North Atlantic can occupy up to 4.8 cubic kilometres with fish densities between 0.5 and 1.0 fish/cubic metre. That's several billion fish in one school.
Fish migration
Between May and July huge numbers of
sardineSardines, or pilchards, are several types of small, oily fish related to herrings, family Clupeidae. Sardines are named after the Mediterranean island of Sardinia, around which they were once abundant....
s spawn in the cool waters of the
Agulhas BankThe Agulhas Bank is a broad, shallow part of the southern African continental shelf which extends south of Cape Agulhas before falling away steeply away to the abyssal plain....
and then follow a current of cold water northward along the east coast of South Africa. This great migration, called the
sardine runThe sardine run of southern Africa occurs from May through July when billions of sardines – or more specifically the Southern African pilchard Sardinops sagax – spawn in the cool waters of the Agulhas Bank and move northward along the east coast of South Africa...
, creates spectacular feeding frenzies along the coastline as marine predators, such as dolphins, sharks and gannets attack the schools.
Krill
Most
krillKrill is the common name given to the order Euphausiacea of shrimp-like marine crustaceans. Also known as euphausiids, these small invertebrates are found in all oceans of the world...
, small shrimp-like
crustaceanCrustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s, form large swarms, sometimes reaching densities of 10,000–60,000 individual animals per cubic metre. Swarming is a defensive mechanism, confusing smaller predators that would like to pick out single individuals. Krill typically follow a diurnal
vertical migrationDiel vertical migration, also known as diurnal vertical migration, is a pattern of movement that some organisms living in the ocean and in lakes undertake each day. Usually organisms move up to the epipelagic zone at night and return to the mesopelagic zone of the oceans or to the hypolimnion zone...
. Until recently it has been assumed that they spend the day at greater depths and rise during the night toward the surface. It has been found that the deeper they go, the more they reduce their activity, apparently to reduce encounters with predators and to conserve energy. Later work suggested that swimming activity in krill varied with stomach fullness. Satiated animals that had been feeding at the surface swim less actively and therefor sink below the mixed layer. As they sink they produce faeces which may mean that they have an important role to play in the Antarctic carbon cycle. Krill with empty stomachs were found to swim more actively and thus head towards the surface. This implies that vertical migration may be a bi- or tri-daily occurrence. Some species form surface swarms during the day for feeding and reproductive purposes even though such behaviour is dangerous because it makes them extremely vulnerable to predators. Dense swarms may elicit a
feeding frenzyIn ecology, a feeding frenzy is a situation where oversaturation of a supply of food leads to rapid feeding by predatory animals. For example, a large school of fish can cause nearby sharks to enter a feeding frenzy. This can cause the sharks to go wild, biting anything that moves, including each...
among fish, birds and mammal predators, especially near the surface. When disturbed, a swarm scatters, and some individuals have even been observed to
moultEcdysis is the moulting of the cuticula in many invertebrates. This process of moulting is the defining feature of the clade Ecdysozoa, comprising the arthropods, nematodes, velvet worms, horsehair worms, rotifers, tardigrades and Cephalorhyncha...
instantaneously, leaving the
exuviaExuviae is a term used in biology to describe the remains of an exoskeleton and related structures that are left after ecdysozoans have moulted...
behind as a decoy.
Copepods
CopepodCopepods are a group of small crustaceans found in the sea and nearly every freshwater habitat. Some species are planktonic , some are benthic , and some continental species may live in limno-terrestrial habitats and other wet terrestrial places, such as swamps, under leaf fall in wet forests,...
s are a group of tiny
crustaceanCrustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s found in the sea and lakes. Many species are
planktonPlankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...
ic (drifting in sea waters), and others are
benthicBenthos is the community of organisms which live on, in, or near the seabed, also known as the benthic zone. This community lives in or near marine sedimentary environments, from tidal pools along the foreshore, out to the continental shelf, and then down to the abyssal depths.Many organisms...
(living on the ocean floor). Copepods are typically 1 to 2 mm (0.0393700787401575 to 0.078740157480315 in) long, with a teardrop shaped body and large
antennaeAntennae in biology have historically been paired appendages used for sensing in arthropods. More recently, the term has also been applied to cilium structures present in most cell types of eukaryotes....
. Although like other crustaceans they have an armoured
exoskeletonAn exoskeleton is the external skeleton that supports and protects an animal's body, in contrast to the internal skeleton of, for example, a human. In popular usage, some of the larger kinds of exoskeletons are known as "shells". Examples of exoskeleton animals include insects such as grasshoppers...
, they are so small that in most species this thin armour, and the entire body, is almost totally transparent. Copepods have a compound, median single eye, usually bright red, in the centre of the transparent head.
Copepods also swarm. For example, monospecific swarms have been observed regularly around
coral reefCoral reefs are underwater structures made from calcium carbonate secreted by corals. Coral reefs are colonies of tiny living animals found in marine waters that contain few nutrients. Most coral reefs are built from stony corals, which in turn consist of polyps that cluster in groups. The polyps...
s and sea grass, and in lakes. Swarms densities were about one million copepods per cubic metre. Typical swarms were one or two metres in diameter, but some exceeded 30 cubic metres. Copepods need visual contact to keep together, and they disperse at night.
Spring produces
bloomsAn algal bloom is a rapid increase or accumulation in the population of algae in an aquatic system. Algal blooms may occur in freshwater as well as marine environments. Typically, only one or a small number of phytoplankton species are involved, and some blooms may be recognized by discoloration...
of swarming
phytoplanktonPhytoplankton are the autotrophic component of the plankton community. The name comes from the Greek words φυτόν , meaning "plant", and πλαγκτός , meaning "wanderer" or "drifter". Most phytoplankton are too small to be individually seen with the unaided eye...
which provide food for copepods. Planktonic copepods are usually the dominant members of the
zooplanktonZooplankton are heterotrophic plankton. Plankton are organisms drifting in oceans, seas, and bodies of fresh water. The word "zooplankton" is derived from the Greek zoon , meaning "animal", and , meaning "wanderer" or "drifter"...
, and are in turn major food organisms for many other marine animals. In particular, copepods are prey to
forage fishForage fish, also called prey fish or bait fish, are small fish which are preyed on by larger predators for food. Predators include other larger fish, seabirds and marine mammals. Typical ocean forage fish feed near the base of the food chain on plankton, often by filter feeding...
and
jellyfishJellyfish are free-swimming members of the phylum Cnidaria. Medusa is another word for jellyfish, and refers to any free-swimming jellyfish stages in the phylum Cnidaria...
, both of which can assemble in vast, million-strong swarms. Some copepods have extremely fast
escape responseEscape response, escape reaction, or escape behaviour is a possible reaction in response to stimuli indicative of danger, in particular, it initiates an escape motion of an animal...
s when a predator is sensed and can jump with high speed over a few millimetres (see animated image below).
Planktonic copepods are important to the
carbon cycleThe carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth...
. Some scientists say they form the largest animal
biomassBiomass, as a renewable energy source, is biological material from living, or recently living organisms. As an energy source, biomass can either be used directly, or converted into other energy products such as biofuel....
on earth. They compete for this title with
Antarctic krillAntarctic krill, Euphausia superba, is a species of krill found in the Antarctic waters of the Southern Ocean. It is a shrimp-like crustacean that lives in large schools, called swarms, sometimes reaching densities of 10,000–30,000 individual animals per cubic metre...
. Because of their smaller size and relatively faster growth rates, however, and because they are more evenly distributed throughout more of the world's oceans, copepods almost certainly contribute far more to the secondary productivity of the world's oceans, and to the global ocean carbon sink than
krillKrill is the common name given to the order Euphausiacea of shrimp-like marine crustaceans. Also known as euphausiids, these small invertebrates are found in all oceans of the world...
, and perhaps more than all other groups of organisms together. The surface layers of the oceans are currently believed to be the world's largest carbon sink, absorbing about 2 billion tons of carbon a year, the equivalent to perhaps a third of
human carbon emissionsA greenhouse gas is a gas in an atmosphere that absorbs and emits radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. The primary greenhouse gases in the Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone...
, thus reducing their impact. Many planktonic copepods feed near the surface at night, then sink into deeper water during the day to avoid visual predators. Their moulted exoskeletons, faecal pellets and respiration at depth all bring carbon to the deep sea.
Algal blooms
Many single-celled organisms called
phytoplanktonPhytoplankton are the autotrophic component of the plankton community. The name comes from the Greek words φυτόν , meaning "plant", and πλαγκτός , meaning "wanderer" or "drifter". Most phytoplankton are too small to be individually seen with the unaided eye...
live in oceans and lakes. When certain conditions are present, such as high nutrient or light levels, these organisms reproduce explosively. The resulting dense swarm of phytoplankton is called an
algal bloomAn algal bloom is a rapid increase or accumulation in the population of algae in an aquatic system. Algal blooms may occur in freshwater as well as marine environments. Typically, only one or a small number of phytoplankton species are involved, and some blooms may be recognized by discoloration...
. Blooms can cover hundreds of square kilometres and are easily seen in satellite images. Individual phytoplankton rarely live more than a few days, but blooms can last weeks.
Bacteria
Swarming is also used to describe groupings of some kinds of bacteria such as
myxobacteriaThe myxobacteria are a group of bacteria that predominantly live in the soil. The myxobacteria have very large genomes, relative to other bacteria, e.g. 9-10 million nucleotides. Sorangium cellulosum has the largest known bacterial genome, at 13.0 million nucleotides...
. Myxobacteria swarm together in "wolf packs", actively moving using a process known as
bacterial glidingBacterial gliding is a process whereby a bacterium can move under its own power. This process does not involve the use of flagella, which is a more common means of motility in bacteria...
and keeping together with the help of intercellular molecular signals.
Quadrupeds
People
A collection of people can also exhibit swarm behaviour, such as pedestrians or soldiers swarming the parapets. In Cologne, Germany, two biologists from the University of Leeds demonstrated flock like behaviour in humans. The group of people exhibited similar behavioural pattern to a flock, where if five percent of the flock changed direction the others would follow. If one person was designated as a predator and everyone else was to avoid him, the flock behaved very much like a school of fish. Understanding how humans interact in crowds is important if crowd management is to effectively avoid casualties at football grounds, music concerts and subway stations.
The mathematical modelling of flocking behaviour is a common technology, and has found uses in animation. Flocking simulations have been used in many films to
generate crowdsCrowd simulation is the process of simulating the movement of a large number of objects or characters, now often appearing in 3D computer graphics for film...
which move realistically. Tim Burton's
Batman ReturnsBatman Returns is a 1992 American superhero film directed by Tim Burton. Based on the DC Comics character Batman, it is the sequel to Burton's Batman , and features Michael Keaton reprising the title role, with Danny DeVito as the Penguin and Michelle Pfeiffer as Catwoman.Burton originally did not...
was the first movie to make use of swarm technology for rendering, realistically depicting the movements of a group of bats using the
boidsBoids is an artificial life program, developed by Craig Reynolds in 1986, which simulates the flocking behaviour of birds. His paper on this topic was published in 1987 in the proceedings of the ACM SIGGRAPH conference...
system. The
Lord of the Rings film trilogyThe Lord of the Rings is an epic film trilogy consisting of three fantasy adventure films based on the three-volume book of the same name by English author J. R. R. Tolkien. The films are The Fellowship of the Ring , The Two Towers and The Return of the King .The films were directed by Peter...
made use of similar technology, known as massive, during battle scenes. Swarm technology is particularly attractive because it is cheap, robust, and simple.
An ant-based computer simulation using only six interaction rules has also been used to evaluate aircraft boarding behaviour.
Also, ants provided some guidance for
Douglas A. LawsonDouglas A. Lawson is a geologist, paleontologist, and computer scientist.In 1971, Lawson discovered a partial wing Douglas A. Lawson (born 1947) is a geologist, paleontologist, and computer scientist.In 1971, Lawson discovered a partial wing Douglas A. Lawson (born 1947) is a geologist,...
, a systems analyst at Southwest Airlines.
:"Because we know that ants have accomplished these amazing things right based on very simple rules, we know that if we want to see something complicated happen - like completely filling the interior of an aircraft with people - we know that simple ant-type behavior is adequate to represent what's occurring," Lawson said.
"So Southwest Airlines said, 'Help us figure out the most efficient way to help us get our passengers on a plane,' and you said, 'I know - I'll use ants'?" asked Salie.
"Yeah, right. Because they do complicated things with very simple rules," Lawson said.
Lawson used mathematically-modeled ants to determine the most efficient way of boarding a plane, which turns out to be open seating.
"So Southwest's way of boarding without seat numbers is actually more efficient than when I board another airline and know exactly what my seat is?" asked Salie.
"Right. When we simulated what the different airlines are doing, it turns out that with assigned seats, there's a one-third chance that you're going to ask two people to get up, whereas open seating - since the middle seat is the undesirable one - generally that's the one that's last to be filled, [so] only one person is likely to get up, the person sitting near the aisle," said Lawson. "I may have to ask somebody to get up and get out of the way to let me get to a seat, and that's about it. So it's really
simple.
"So the ants are sort of an analogy - simple rules produce complicated transactions and events and major structures. and we can do the same thing in a little simulated world and represent very complicated processes," said Lawson.
Airlines have also used ant-based routing in assigning aircraft arrivals to airport gates. An airline system developed by
Douglas A. LawsonDouglas A. Lawson is a geologist, paleontologist, and computer scientist.In 1971, Lawson discovered a partial wing Douglas A. Lawson (born 1947) is a geologist, paleontologist, and computer scientist.In 1971, Lawson discovered a partial wing Douglas A. Lawson (born 1947) is a geologist,...
uses swarm theory, or
swarm intelligenceSwarm intelligence is the collective behaviour of decentralized, self-organized systems, natural or artificial. The concept is employed in work on artificial intelligence...
– the idea that a colony of ants works better than one alone. Each pilot acts like an ant searching for the best airport gate. "The pilot learns from his experience what's the best for him, and it turns out that that's the best solution for the airline," Lawson explains. As a result, the "colony" of pilots always go to gates they can arrive and depart quickly. The program can even alert a pilot of plane back-ups before they happen. "We can anticipate that it's going to happen, so we'll have a gate available," says Lawson.
Swarm behaviour also occurs in
traffic flowTraffic flow, in mathematics and civil engineering, is the study of interactions between vehicles, drivers, and infrastructure , with the aim of understanding and developing an optimal road network with efficient movement of traffic and minimal traffic congestion problems.-History:Attempts to...
dynamics, such as the
traffic waveTraffic waves, also called stop waves or traffic shocks, are travelling disturbances in the distribution of cars on a highway. Traffic waves usually travel backwards in relation to the motion of the cars themselves, or "upstream". The waves can also travel downstream, however, more commonly become...
.
Bidirectional trafficIn transportation infrastructure, a bidirectional traffic system divides travelers into two streams of traffic that flow in opposite directions....
can be observed in
antAnts are social insects of the family Formicidae and, along with the related wasps and bees, belong to the order Hymenoptera. Ants evolved from wasp-like ancestors in the mid-Cretaceous period between 110 and 130 million years ago and diversified after the rise of flowering plants. More than...
trails. In recent years this behaviour has been researched for insight into pedestrian and traffic models. Simulations based on pedestrian models have also been applied crowds which stampede because of panic.
Herd behaviour in
marketingMarketing is the process used to determine what products or services may be of interest to customers, and the strategy to use in sales, communications and business development. It generates the strategy that underlies sales techniques, business communication, and business developments...
is used to explain the dependencies of customers' mutual behaviour.
The EconomistThe Economist is an English-language weekly news and international affairs publication owned by The Economist Newspaper Ltd. and edited in offices in the City of Westminster, London, England. Continuous publication began under founder James Wilson in September 1843...
reported a recent conference in
RomeRome is the capital of Italy and the country's largest and most populated city and comune, with over 2.7 million residents in . The city is located in the central-western portion of the Italian Peninsula, on the Tiber River within the Lazio region of Italy.Rome's history spans two and a half...
on the subject of the simulation of adaptive human behaviour. It shared mechanisms to increase impulse buying and get people "to buy more by playing on the herd instinct." The basic idea is that people will buy more of products that are seen to be popular, and several feedback mechanisms to get product popularity information to consumers are mentioned, including
smart cardA smart card, chip card, or integrated circuit card , is any pocket-sized card with embedded integrated circuits. A smart card or microprocessor cards contain volatile memory and microprocessor components. The card is made of plastic, generally polyvinyl chloride, but sometimes acrylonitrile...
technology and the use of Radio Frequency Identification Tag technology. A "swarm-moves" model was introduced by a
Florida Institute of TechnologyFlorida Institute of Technology, also known as Florida Tech, is an independent private technical research university located in Melbourne, Florida, United States. Founded in 1958 as Brevard Engineering College, the institute has been known by its present name since 1966. Florida Tech's curriculum...
researcher, which is appealing to supermarkets because it can "increase sales without the need to give people discounts."
Robotics
The application of swarm principles to
robotA robot is a mechanical or virtual intelligent agent that can perform tasks automatically or with guidance, typically by remote control. In practice a robot is usually an electro-mechanical machine that is guided by computer and electronic programming. Robots can be autonomous, semi-autonomous or...
s is called
swarm roboticsSwarm robotics is a new approach to the coordination of multirobot systems which consist of large numbers of mostly simple physical robots. It is supposed that a desired collective behavior emerges from the interactions between the robots and interactions of robots with the environment...
, while swarm intelligence refers to the more general set of algorithms.
Inspired by
colonies of insectsIn biology, a colony reference to several individual organisms of the same species living closely together, usually for mutual benefit, such as stronger defense or the ability to attack bigger prey. Some insects live only in colonies...
such as ants and bees, researchers are modelling the behaviour of
swarmsSwarm robotics is a new approach to the coordination of multirobot systems which consist of large numbers of mostly simple physical robots. It is supposed that a desired collective behavior emerges from the interactions between the robots and interactions of robots with the environment...
of thousands of tiny robots which together perform a useful task, such as finding something hidden, cleaning, or spying. Each robot is quite simple, but the emergent behaviour of the swarm is more complex. The whole set of robots can be considered as one single distributed system, in the same way an ant colony can be considered a
superorganismA superorganism is an organism consisting of many organisms. This is usually meant to be a social unit of eusocial animals, where division of labour is highly specialised and where individuals are not able to survive by themselves for extended periods of time. Ants are the best-known example of...
, exhibiting
swarm intelligenceSwarm intelligence is the collective behaviour of decentralized, self-organized systems, natural or artificial. The concept is employed in work on artificial intelligence...
. The largest swarms so far created include the
iRobotiRobot Corporation is an American advanced technology company founded in 1990 and incorporated in Delaware in 2000, the iRobot Corporation designs robots such as an autonomous home vacuum cleaner , the Scooba that scrubs and cleans hard floors, and military and police robots, such as the PackBot...
swarm, the SRI/MobileRobots CentiBots project and the Open-source Micro-robotic Project swarm, which are being used to research collective behaviours. Swarms are also more resistant to failure. Whereas one large robot may fail and ruin a mission, a swarm can continue even if several robots fail. This could make them attractive for space exploration missions, where failure is normally extremely costly.
The I-Swarm project aims to develop a large scale
swarmSwarm behaviour, or swarming, is a collective behaviour exhibited by animals of similar size which aggregate together, perhaps milling about the same spot or perhaps moving en masse or migrating in some direction. As a term, swarming is applied particularly to insects, but can also be applied to...
of up to 1,000 small
microrobotsMicrobotics is the field of miniature robotics, in particular mobile robots with characteristic dimensions less than 1 mm...
, about 2 x 2 x 1 mm in size. The small size means that
sensorySensory may refer to:relating to senses or smellIn biology:* Sensory preference* Sensory system, part of the nervous system of organisms* Sensory neuron, nerve cell responsible for transmitting information about external stimuli...
and computational capabilities will be limited. This will be compensated for by the emergent swarm effects. The robots operate on
solar powerSolar energy, radiant light and heat from the sun, has been harnessed by humans since ancient times using a range of ever-evolving technologies. Solar radiation, along with secondary solar-powered resources such as wind and wave power, hydroelectricity and biomass, account for most of the available...
and can communicate between each other. The robots will differ in the type of sensors, manipulators and the amount of computational power. The swarm is expected to have many applications, including micro assembly, biological, medical or cleaning tasks.
Military
Military swarmingMilitary swarming is a behavior where autonomous, or semi-autonomous, units of action attack an enemy from several different directions and then regroup. Pulsing, where the units shift the point of attack, is a part of military swarming. Swarming is not limited to the human military realm...
is a behaviour where autonomous or partially autonomous units of action attack an enemy from several different directions and then regroup.
Pulsing, where the units shift the point of attack, is also a part of military swarming. Military swarming involves the use of a decentralized force against an opponent, in a manner that emphasizes mobility, communication, unit autonomy and coordination or synchronization. Historically military forces used principles of swarming without really examining them explicitly, but now active research consciously examines military doctrines that draw ideas from swarming.
Merely because multiple units converge on a target, they are not necessarily swarming. Siege operations do not involve swarming, because there is no manoeuvre; there is convergence but on the besieged fortification. Nor do
guerilla ambushesGuerrilla warfare is a form of irregular warfare and refers to conflicts in which a small group of combatants including, but not limited to, armed civilians use military tactics, such as ambushes, sabotage, raids, the element of surprise, and extraordinary mobility to harass a larger and...
constitute swarms, because they are "hit-and-run". Even though the ambush may have several points of attack on the enemy, the guerillas withdraw when they either have inflicted adequate damage, or when they are endangered.
Myths
- There is a popular myth that lemming
Lemmings are small rodents, usually found in or near the Arctic, in tundra biomes. They are subniveal animals, and together with voles and muskrats, they make up the subfamily Arvicolinae , which forms part of the largest mammal radiation by far, the superfamily Muroidea, which also includes rats,...
s commit mass suicide- Examples :Mass suicide sometimes occurs in religious or cultic settings. Defeated groups may resort to mass suicide rather than being captured. Suicide pacts are a form of mass suicide unconnected to cults or war that are sometimes planned or carried out by small groups of frustrated people...
by swarming off cliffs when they migrate. Driven by strong biological urges, some species of lemmings may migrate in large groups when population density becomes too great. Lemmings can swim and may choose to cross a body of water in search of a new habitat. In such cases, many may drown if the body of water is so wide as to stretch their physical capability to the limit. This fact combined with an unexplained fluctuations in the population of Norwegian lemmings gave rise to the myth.
- Piranha
A piranha or piraña is a member of family Characidae in order Characiformes, an omnivorous freshwater fish that inhabits South American rivers. In Venezuela, they are called caribes...
have a reputation as fearless fish that swarm in ferocious and predatory packs. However, recent research, which started "with the premise that they school as a means of cooperative hunting", discovered that they were in fact rather fearful fish, like other fish, who schooled for protection from their predators, such as cormorants, caimans and dolphins. Piranhas are "basically like regular fish with large teeth".
See also
- Dyson swarm
- List of collective nouns
- Mobile Bay jubilee
Jubilee is the name used locally for a natural phenomenon that occurs sporadically on the shores of Mobile Bay, a large body of water on Alabama's Gulf Coast. During a jubilee many species of crab and shrimp, as well as flounder, eels, and other demersal fish will leave deeper waters and swarm—in...
- Swarm (simulation)
Swarm is the name of a multi-agent simulation package, useful for simulating the interaction of agents and their emergent collective behaviour. Swarm was initially developed at the Santa Fe Institute in the mid-1990s, and since 1999 has been maintained by the non-profit Swarm Development...
- Traffic wave
Traffic waves, also called stop waves or traffic shocks, are travelling disturbances in the distribution of cars on a highway. Traffic waves usually travel backwards in relation to the motion of the cars themselves, or "upstream". The waves can also travel downstream, however, more commonly become...
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