{{unreferenced, date=July 2013 In

ethology Ethology is a branch of zoology that studies the behavior, behaviour of non-human animals. It has its scientific roots in the work of Charles Darwin and of American and German ornithology, ornithologists of the late 19th and early 20th cen ...

, an aggregation is any form of gathering of

organisms An organism is any living thing that functions as an individual. Such a definition raises more problems than it solves, not least because the concept of an individual is also difficult. Many criteria, few of them widely accepted, have been pr ...

and the process of coming together. In some forms groups of unrelated species might form, in which interaction between members of the aggregation might be minimal; for example herds of grazing

zebra Zebras (, ) (subgenus ''Hippotigris'') are African equines with distinctive black-and-white striped coats. There are three living species: Grévy's zebra (''Equus grevyi''), the plains zebra (''E. quagga''), and the mountain zebra (''E. ...

and

antelopes The term antelope refers to numerous extant or recently extinct species of the ruminant artiodactyl family Bovidae that are indigenous to most of Africa, India, the Middle East, Central Asia, and a small area of Eastern Europe. Antelopes do no ...

might combine, both the better to observe the approach of

predators Predation is a biological interaction in which one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill ...

, and to improve the odds of escape in the event of attack by predators. Sometimes there might be some interaction, such as mixed flocks of birds that observe each other's foraging behaviour in searching for food. Sometimes there might be quite orderly common action, such as the queuing up for a resource; for example different species of fishes may aggregate around a

cleaning station A cleaning station is a location where aquatic life congregate to be cleaned by smaller beings. Such stations exist in both freshwater and marine environments, and are used by animals including fish, sea turtles and hippos. The cleaning process ...

where cleaner wrasse and

cleaner shrimp Cleaner shrimp is a common name for a number of swimming Decapoda, decapod crustaceans that clean other organisms of parasites. Most are found in the family (biology), families Hippolytidae (including the Pacific cleaner shrimp, ''Lysmata amboi ...

are active, more or less taking turns for attention. Such aggregations, where there is no particular association of species or sizes, may be referred to loosely as unstructured aggregations. Commonly they are very temporary and may be loose, with flocks or herds associating casually and separating equally casually within hours. Structured aggregations tend to be longer-term and of a specific life-cycle function and context. Typically, though not necessarily, they will be of a single species. Often they will be of a single age and possibly of a single sex, such as shoals of fish fry that have specific ecological requirements that are not compatible with those of the mature species. One class of such aggregations comprises groups of adult, but immature "bachelor" males of elephants, seals, lions and other animals in which the mature herd will not tolerate males that would begin to compete with the dominant males. Another is when aposematic larvae of certain insects such as some

Lepidoptera Lepidoptera ( ) or lepidopterans is an order (biology), order of winged insects which includes butterflies and moths. About 180,000 species of the Lepidoptera have been described, representing 10% of the total described species of living organ ...

and

Hemiptera Hemiptera (; ) is an order of insects, commonly called true bugs, comprising more than 80,000 species within groups such as the cicadas, aphids, planthoppers, leafhoppers, assassin bugs, bed bugs, and shield bugs. They range in size from ...

form a flock that feed together and may migrate in "processions" until they are mature after which some kinds disperse. Most species of migrating birds and mammals flock on a large scale, partly for protection and partly for greater reliability of navigation. In some species of Hemiptera the adults remain with their aggregated immature offspring, sometimes in protective roles. The range of functions is very wide in detail, but among the more important classes of function are security against predators, success in food location, wide range of

mate choice Mate choice is one of the primary mechanisms under which evolution can occur. It is characterized by a "selective response by animals to particular stimuli" which can be observed as behavior.Bateson, Paul Patrick Gordon. "Mate Choice." Mate Choi ...

, with concomitant increase of

outbreeding Out-crossing or out-breeding is the technique of crossing between different breeds. This is the practice of introducing distantly related genetic material into a breeding line, thereby increasing genetic diversity. Outcrossing in animals Out ...

opportunities, location with other members of the same species (sometimes adherence to separate communities can almost amount to parapatric residence when say, different communities of rats or chimpanzees have violent mutual antipathy). There also are various forms of educational function, such as in some species where the young must learn the correct mate recognition skills, and in highly intelligent species such as crows and elephants, must learn the necessary social skills and the necessary traditional foraging techniques in their region. Aggregation activities are not restricted to the animal kingdom; for one example, a fundamental class of aggregations occurs in the various groups of

slime mold Slime mold or slime mould is an informal name given to a polyphyletic assemblage of unrelated eukaryotic organisms in the Stramenopiles, Rhizaria, Discoba, Amoebozoa and Holomycota clades. Most are near-microscopic; those in the Myxogastria ...

s, in which separate cells actually aggregate in the process of constructing their reproductive structure.

See also