Territory (animal)
This article's lead section may be too short to adequately summarize the key points. (November 2016) |
In
Territoriality is only shown by a minority of species. More commonly, an individual or a group of animals occupies an area that it habitually uses but does not necessarily defend; this is called its home range. The home ranges of different groups of animals often overlap, and in these overlap areas the groups tend to avoid each other rather than seeking to confront and expel each other. Within the home range there may be a core area that no other individual group uses, but, again, this is as a result of avoidance.
Function
The ultimate function of animals inhabiting and defending a territory is to increase the individual fitness or inclusive fitness of the animals expressing the behaviour. Fitness in this biological sense relates to the ability of an animal to survive and raise young. The proximate functions of territory defense vary. For some animals, the reason for such protective behaviour is to acquire and protect food sources, nesting sites, mating areas, or to attract a mate.
Types and size
Among birds, territories have been classified as six types.[1]
- Type A: An 'all-purpose territory' in which all activities occur, e.g. courtship, mating, nesting and foraging
- Type B: A mating and nesting territory, not including most of the area used for foraging.
- Type C: A nesting territory which includes the nest plus a small area around it. Common in colonial waterbirds.
- Type D: A pairing and mating territory. The type of territory defended by males in lekking species.
- Type E: Roosting territory.
- Type F: Winter territory which typically includes foraging areas and roost sites. May be equivalent (in terms of location) to the Type A territory, or for a migratory species, may be on the wintering grounds.
Reports of territory size can be confused by a lack of distinction between home range and the defended territory. The size and shape of a territory can vary according to its purpose, season, the amount and quality of resources it contains, or the geography. The size is usually a compromise of resource needs, defense costs, predation pressure and reproductive needs.
Some species of
In birds,
Territories can be linear. Sanderlings (Calidris alba) forage on beaches and sandflats. When on beaches, they feed either in flocks or individual territories of 10 to 120 metres of shoreline.[6]
The time to develop territories varies between animals. The marine iguana (Amblyrhynchus cristatus) is a lekking reptile. Males start to establish small display territories two months ahead of the mating season.[7]
Retaining a territory
Rather than retaining a territory simply by fighting, for some animals this can be a 3-stage process. Many animals create "sign-posts" to advertise their territory. Sometimes these sign-posts are on the boundary thereby demarcating the territory, or, may be scattered throughout the territory. These communicate to other animals that the territory is occupied and may also communicate additional information such as the sex, reproductive status or
Advertising the territory
Scent marking
Scent marking, also known as territorial marking or
Territorial scent marking may involve behaviours specific to this activity. When
In the Eastern carpenter bee, Xylocopa virginica, both sexes have glands that evolved for marking the nest. Males, although they have the gland, are unable to produce the marking substance. Females secrete it near the nest site entrance to establish their territory.[21]
Wombats use feces to mark their territory. They have evolved specialized intestinal anatomy to produce cubical feces to ensure the feces do not roll away.[22]
Visual
Visual sign-posts may be a short-term or long-term mode of advertising a territory. Short-term communication includes the colouration or behaviour of the animal, which can only be communicated when the resident is present. Other animals may use more long-term visual signals such as faecal deposits, or marks on the vegetation or ground. Visual marking of territory is often combined with other modes of animal communication.
Some animals have prominent "badges" or visual displays to advertise their territory, often in combination with scent marking or auditory signals. Male
After leaving a urination mark, some animals scrape or dig the ground nearby, thereby leaving a visual advertisement of the territory. This includes domestic dogs.
Several species scratch or chew trees leaving a visual mark of their territory. This is sometimes combined with rubbing on the tree which may leave tufts of fur. These include the Canada lynx (Lynx canadensis)[27] and the American black bear (Ursus americanus).[28][29] Many animals have scent glands in their paws or deposit fur during tree-marking, so tree-marking may be a combination of both visual and olfactory advertising of the territory. The male ring-tailed lemur has a specialised adaptation to assist in leaving visual/olfactory territorial marks. On their inner forearm (antebrachial) is a scent gland which is covered by a spur. In a behaviour called "spur marking", they grasp the substrate, usually a small sapling, and drag the spur over it, cutting into the wood and spreading the gland's secretions. When on the ground, ring-tailed lemurs preferentially mark small saplings and when high in the trees, they usually mark small vertical branches.[20]
European wildcats (Felis silvestris) deposit their faecal marks on plants with high visual conspicuousness that enhances the visual effectiveness of the signal.[30]
Auditory
Many animals use vocalisations to advertise their territory. These are short-term signals transmitted only when the animal is present, but can travel long distances and over varied habitats. Examples of animals which use auditory signals include birds, frogs and canids.
Ritualized aggression
Animals use a range of behaviours to intimidate intruders and defend their territories, but without engaging in fights which are expensive in terms of energy and the risk of injury. This is ritualized aggression. Such defense frequently involves a graded series of behaviours or displays that include threatening gestures (such as vocalizations, spreading of wings or gill covers, lifting and presentation of claws, head bobbing, tail and body beating) and finally, direct attack.
Defense
Territories may be held by an individual, a
Strategies
Animals may use several strategies to defend their territories.
The first game theory model of fighting is known as the hawk-dove game. This model pits a hawk strategy (always try to injure your opponent and only withdraw from the contest if an injury is received) against a dove strategy (always use a non-injurious display if the rival is another dove and always withdraw if the rival is a hawk).
Another strategy used in territory defence is the war of attrition. In this model of aggression, two contestants compete for a resource by persisting while constantly accumulating costs over the time that the contest lasts. Strategically, the game is an auction in which the prize goes to the player with the highest bid, and each player pays the loser's low bid.
Some animals use a strategy termed the dear enemy effect in which two neighbouring territorial animals become less aggressive toward one another once territorial borders are well-established and they are familiar to each other, but aggression toward unfamiliar animals remains unaffected.[35] The converse of this is the nasty neighbour effect in which a territory-holder shows heightened aggression toward neighbouring territory-holders but unaffected aggression to unfamiliar animals or distant territory-holders. These contrasting strategies depend on which intruder (familiar or unfamiliar) poses the greatest threat to the resident territory-holder.[36]
In territory defence by groups of animals, reciprocal altruism can operate whereby the cost to the benefactor in helping defend the territory is less than the gains to the beneficiary.
Resources defended
An animal chooses its territory by deciding what part of its home range it will defend. In selecting a territory, the size and quality play crucial roles in determining an animal's habitat. Territory size generally tends to be no larger than the organism requires to survive, because defending a larger territory incurs greater energy, time and risk of injury costs. For some animals, the territory size is not the most important aspect of territoriality, but rather the quality of the defended territory.
Behavioural ecologists have argued that food distribution determines whether a species is territorial or not, however, this may be too narrow a perspective. Several other type of resource may be defended including partners, potential mates, offspring, nests or lairs, display areas or
Several types of resource in a territory may be defended.
Food: Large solitary (or paired) carnivores, such as bears and the bigger raptors require an extensive protected area to guarantee their food supply. This territoriality only breaks down when there is a glut of food, for example when grizzly bears are attracted to migrating salmon.
Food related territoriality is least likely with insectivorous birds, where the food supply is plentiful but unpredictably distributed. Swifts rarely defend an area larger than the nest. Conversely, other insectivorous birds that occupy more constrained territories, such as the ground-nesting blacksmith lapwing may be very territorial, especially in the breeding season during which they not only threaten or attack many kinds of intruders, but have stereotyped display behaviour to deter conspecifics sharing neighbouring nesting spots.
The
Nests and offspring: Many birds, particularly seabirds, nest in dense communities but are nonetheless territorial in defending their nesting site to within the distance they can reach while brooding. This is necessary to prevent attacks on their own chicks or nesting material from neighbours. Commonly the resulting superimposition of the short-range repulsion onto the long-range attraction characteristically leads to the well-known roughly hexagonal spacing of nests. One gets a similar hexagonal spacing resulting from the territorial behaviour of gardening limpets such as species of Scutellastra.[39] They vigorously defend their gardens of particular species of algae, that extend for perhaps 1–2 cm around the periphery of their shells.
The desert grass spider, Agelenopsis aperta, often engages in fights over its territory and the most combative spiders have the largest territories.[40]
Some species of penguin defend their nests from intruders trying to steal the pebbles from which the nest is constructed.[5]
Mating opportunities: The striped mouse (
Territory defence in male variegated pupfish (Cyprinodon variegatus) is dependent on the presence of females. Reduced aggression consistent with the dear enemy effect occurs between conspecific neighbours in the absence of females, but the presence of a female in a male's territory instigates comparably greater aggression between the neighbours.[44]
In the
Some species of bees also exhibit territoriality to defend mating sites. For example, in Euglossa imperialis, a non-social bee species, males have been observed to occasionally form aggregations of fragrance-rich territories, considered to be leks. These leks serve only a facultative purpose for this species, in which the more fragrance-rich sites there are, the greater the number of habitable territories. Since these territories are aggregated, females have a large selection of males with whom to potentially mate within the aggregation, giving females the power of mate choice.[46] Similar behaviour is also observed in the Eulaema meriana orchid bee. Males in this species of bee show alternative behaviours of territoriality and transiency. Transient male bees did not defend territories, but instead flew from one territory to the other. They also did not engage in physical contact with the territorial males. On the other hand, territorial males patrolled an area around a tree and used the same territory for up to 49 days. It also appeared that they gave up territories to new males without violence. Males defend territories solely for mating, and no other resources such as fragrances, nests, nest construction materials, nectar, or pollen are found at these territories.[47]
Single resource territories
Although most territories contain multiple (potential) resources, some territories are defended for only one purpose. European blackbirds may defend feeding territories that are distant from their nest sites, and in some species that form leks, for example in the Uganda kob (a grazing antelope) and the marine iguana, males defend the lek site which is used only for mating.
Polyterritoriality
Many species demonstrate polyterritoriality, referring to the act of claiming or defending more than one territory. In the European pied flycatcher (Ficedula hypoleuca), researchers assert that males exhibit polyterritoriality to deceive females of the species into entering into polygynous relationships. This hypothesis, named the deception hypothesis, claims that males have territories at distances sufficiently great that females are unable to discern already-mated males. The observation that males travelled long distances, ranging from 200m to 3.5 km, to find a second mate supports this argument.[48] The debate about polyterritoriality in this species may initiate research about the evolution and reasons for polyterritoriality in other unrelated species.
See also
- Aggression
- Alpha (biology)
- Biological interaction
- Border control
- Dear enemy recognition
- Home range
- Property
- The Territorial Imperative
References
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Further reading
- Walther, F. R., E. C. Mungall, G. A. Grau. (1983) Gazelles and their relatives : a study in territorial behavior Park Ridge, N.J. : Noyes Publications 239, ISBN 0-8155-0928-6
- Stokes, A. W. (editor) (1974) Territory Stroudsburg, Pa., Dowden, Hutchinson & Ross 398, ISBN 0-87933-113-5
- Klopfer, P. H. (1969) Habitats and territories; a study of the use of space by animals New York, Basic Books 117 p.