Territoriality
Territoriality
Territorial ownership is another facet of sociality in animal populations. A territory is a fixed area from which intruders of the same species are excluded. This exclusion involves defending the area from intruders and spending long periods of time being conspicuous on the site. Territorial defense has been observed in numerous animals: insects, crustaceans, fishes, amphibians, lizards, birds, and mammals, including humans.
Sometimes the space defended moves with the individual. Individual distance, as it is called, can be observed as the spacing between swallows or pigeons on a wire, gulls lined up on the beach, or people lined up for a bus.
Territoriality is generally an alternative to dominance behavior, although both systems may be observed operating in the same species. A territorial system may work well when the population is low, but it may break down with increasing population density and be replaced with dominance hierarchies in which all animals occupy the same space.
Like every other competitive endeavor, territoriality carries both costs and advantages. It is beneficial when it ensures access to limited resources, unless the territorial boundaries cannot be maintained with little effort. The presumed benefits of a territory are, in fact, numerous: uncontested access to a foraging area; enhanced attractiveness to females thus reducing the problems of pairbonding, mating, and rearing the young; reduced disease transmission; reduced vulnerability to predators. But the advantages of holding a territory begin to wane if the individual must spend most of the time in boundary disputes with neighbors.
Most of the time and energy required for territoriality are expended when the territory is first established. Once the boundaries are located they tend to be respected, and aggressive behavior diminishes as territorial neighbors come to recognize each other. Indeed, neighbors may look so peaceful that an observer who was not present when the territories were established may conclude (incorrectly) that the animals are not territorial. A “beachmaster” sea lion (that is, a dominant male with many females) seldom quarrels with his neighbors who have their own territories to defend. However, he must be constantly vigilant against bachelor bulls who challenge the beachmaster for mating privileges.
Birds are conspicuously territorial. Most male songbirds establish territories in the early spring and defend these vigorously against all males of the same species during spring and summer when mating and nesting are at their height. A male song sparrow, for example, has a territory of approximately three-fourths of an acre. In any given area, the number of song sparrows remains approximately the same each year. The population remains stable because the young occupy territories of adults that die or are killed. Any surplus in the song sparrow population is excluded from territories and thus not able to mate or nest.
Sea birds such as gulls, gannets, boobies, and albatrosses occupy colonies that are divided into very small territories just large enough for nesting (Figure 38-17). The territories of these birds cannot include their fishing grounds, since they all forage in the sea where the food is always shifting in location and shared by all.
Territorial behavior is not as prominent with mammals as it is with birds. Mammals are less mobile than birds, making it more difficult for them to patrol a territory for trespassers. Instead, many mammals have home ranges. A home range is the total area an individual traverses in its activities. It is not an exclusive, defended preserve but overlaps with the home ranges of other individuals of the same species.
For example, home ranges of baboon troops overlap extensively, although a small part of each range becomes the recognized territory of each troop for its exclusive use. Home ranges may shift considerably with the seasons. A baboon troop may have to shift to a new range during the dry season to obtain water and better grass. Elephants, before their movements were restricted by humans, made long seasonal migrations across the African savanna to new feeding ranges. However, the home ranges established for each season are remarkably consistent in size.
Territorial ownership is another facet of sociality in animal populations. A territory is a fixed area from which intruders of the same species are excluded. This exclusion involves defending the area from intruders and spending long periods of time being conspicuous on the site. Territorial defense has been observed in numerous animals: insects, crustaceans, fishes, amphibians, lizards, birds, and mammals, including humans.
Sometimes the space defended moves with the individual. Individual distance, as it is called, can be observed as the spacing between swallows or pigeons on a wire, gulls lined up on the beach, or people lined up for a bus.
Territoriality is generally an alternative to dominance behavior, although both systems may be observed operating in the same species. A territorial system may work well when the population is low, but it may break down with increasing population density and be replaced with dominance hierarchies in which all animals occupy the same space.
Like every other competitive endeavor, territoriality carries both costs and advantages. It is beneficial when it ensures access to limited resources, unless the territorial boundaries cannot be maintained with little effort. The presumed benefits of a territory are, in fact, numerous: uncontested access to a foraging area; enhanced attractiveness to females thus reducing the problems of pairbonding, mating, and rearing the young; reduced disease transmission; reduced vulnerability to predators. But the advantages of holding a territory begin to wane if the individual must spend most of the time in boundary disputes with neighbors.
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| Figure 38-17 Gannet nesting colony. Note precise spacing of nests with each occupant just beyond pecking distance of its neighbors |
Most of the time and energy required for territoriality are expended when the territory is first established. Once the boundaries are located they tend to be respected, and aggressive behavior diminishes as territorial neighbors come to recognize each other. Indeed, neighbors may look so peaceful that an observer who was not present when the territories were established may conclude (incorrectly) that the animals are not territorial. A “beachmaster” sea lion (that is, a dominant male with many females) seldom quarrels with his neighbors who have their own territories to defend. However, he must be constantly vigilant against bachelor bulls who challenge the beachmaster for mating privileges.
Birds are conspicuously territorial. Most male songbirds establish territories in the early spring and defend these vigorously against all males of the same species during spring and summer when mating and nesting are at their height. A male song sparrow, for example, has a territory of approximately three-fourths of an acre. In any given area, the number of song sparrows remains approximately the same each year. The population remains stable because the young occupy territories of adults that die or are killed. Any surplus in the song sparrow population is excluded from territories and thus not able to mate or nest.
Sea birds such as gulls, gannets, boobies, and albatrosses occupy colonies that are divided into very small territories just large enough for nesting (Figure 38-17). The territories of these birds cannot include their fishing grounds, since they all forage in the sea where the food is always shifting in location and shared by all.
Territorial behavior is not as prominent with mammals as it is with birds. Mammals are less mobile than birds, making it more difficult for them to patrol a territory for trespassers. Instead, many mammals have home ranges. A home range is the total area an individual traverses in its activities. It is not an exclusive, defended preserve but overlaps with the home ranges of other individuals of the same species.
For example, home ranges of baboon troops overlap extensively, although a small part of each range becomes the recognized territory of each troop for its exclusive use. Home ranges may shift considerably with the seasons. A baboon troop may have to shift to a new range during the dry season to obtain water and better grass. Elephants, before their movements were restricted by humans, made long seasonal migrations across the African savanna to new feeding ranges. However, the home ranges established for each season are remarkably consistent in size.
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