Structures built by animals
Structures built by non-human animals, often called animal architecture,
Often, these structures incorporate sophisticated features such as
Building behaviour is common in many non-human
Functions
Animals create structures primarily for three reasons:[6]
- to create protected habitats, i.e. homes.
- to catch prey and for foraging, i.e. traps.
- for communication between members of the species (intra-specific communication), i.e. display.
Animals primarily build habitat for protection from extreme temperatures and from predation. Constructed structures raise physical problems which need to be resolved, such as humidity control or ventilation, which increases the complexity of the structure. Over time, through evolution, animals use shelters for other purposes such as reproduction, food storage, etc.[6]
Protected habitats
Predators are attracted to animal-built structures either by the prey or its offspring, or the stored caches of food. Structures built by animals may provide protection from predators through avoiding detection, by means such as camouflage and concealment, or through prevention of invasion, once predators have located the hideout or prey, or a combination of both.[7]: 11 As a last resort, structures may provide means of escape.
Among the structures created by animals to prevent predation are those of the paper wasps, Polistes chinensis antennalis.[8] The nests of these wasps contain “defensive structures”, which are formations built onto or inside of the nest to prevent predation.[8] New nests are formed in the spring by young queens, as worker wasps have not hatched at this time. While these worker wasps are growing in the nest, they are vulnerable to predators who might rip open the nest to eat the larva.[8] One method the queens use to prevent this is covering the developing pupae in pulp, which acts as a reinforcer and makes it more difficult from predators to break open the pupae. This pulp is a mixture of plant matter and liquids from the mouth of the queen wasp.[8] While there are costs associated with using pulp, such as requiring time and energy to collect materials and hindering the emergence of the worker wasps from the cocoon, it does lower the risk of predation. Nests in areas with higher predation rates have been found to contain more pulp on these cocoons than nests in low predation areas.[8]
Animals use the techniques of
Ground-nesting birds which rely on crypsis for concealment have nests made from local materials which blend in with the background, the eggs and young too are cryptic; whereas birds which do not use crypsis for hiding their nests may not have cryptic eggs or young.[9]
In a case apparently of masquerade, the red-faced spinetail Cranioleuca erythrops places bits of grass and other material loosely streaming both above and below the nest chamber to break the shape of the nest and to cause it to resemble random debris without any underlying structure.[10]
Thermoregulation
Temperature extremes harm animals irrespective of whether they are endothermic or ectothermic. In endothermic animals, construction of shelters, coupled with behavioural patterns, reduces the quantity and energy cost of thermoregulation, as in the case of the Arctic ground squirrels.[11]
In ectothermic animals, moderation of temperature, along with architectural modifications to absorb, trap or dissipate energy, maximises the rate of development, as in the case of the communal silk nests of the small eggar moth Eriogaster lanestris. The primary sources of energy for an animal are the sun and its metabolism. The dynamics of heat in animal shelters is influenced by the construction material which may act as a barrier, as a heat sink or to dissipate heat. The cocoons of insect are a case in point.
An interesting example is the case of silk caps which cover the pupal cells of the Oriental hornet
Internal architectural devices, such as walls may block convection or the construction of air flow systems may cool the nest or habitat.
Trap building
Trap-building is a method used to catch prey instead of active hunting.[12] Animals that snare prey will construct a trap and then wait nearby until an organism is caught.[12] This is observed in web-building spiders, who weave elaborate webs of sticky spider silk that entangle prey.[12] Spiders increase the size of their webs when prey are scarce, and can add extra ornamental pieces to their web in order to attract more prey.[12] Traps can allow organisms to capture larger prey, provide protection from predators, or serve as an area for mating, as seen with spiders.[12] Another method of trap creation is used by the antlion (Myrmeleon crudelis) larva.[13] These larva prey on small arthropods, such as ants.[13] The larva dig pits into fine-particle soil to capture their prey, which fall into the holes and are often unable to climb out.[13] The antlions may alter these pits based on prey availability.[13] In areas with less available prey, antlions will make wider holes to increase the chance of catching an insect.[13] If prey are able to climb out of the hole, antlions will increase the depth of the hole.[13]
Displays
Animal structures can serve as a means of communication with other organisms.[14] Animals may construct to attract mates, as seen in species of male fiddler crabs.[14] These crabs may form "pillars" or "hoods" out of sand and mud to gain the attention of nearby females.[14] Bowerbirds (Ptilonorhynchus violaceus) also create display structures to attract mates.[15] During the mating season, male Bowerbirds will collect twigs and colourful objects to create structures known as "bowers", which attract the attention of females.[15] Bowers that are more colourful and well constructed are more attractive to female bowerbirds, as the quality of the constructed bowers reflects the quality of the male bird.[15]
Transportation
Army ants (Eciton hamatum) form "living bridges" to assist in transportation.[16] Army ant colonies may move locations each day in search of food.[16] These bridges provide a path over obstacles and allow for the ants to search for food at an increased speed.[16] The bridges are constructed when the ants join their bodies together, and can vary in size and shape depending on the situation the ants face.[16] Ants are confined to their position when they are forming these bridges, preventing them from moving.[16] The bridges are broken apart when they are no longer needed.[16]
Building materials
Materials used by animals in building structures need to not only be suitable for the kind of structure to be built but also to be manipulable by the animals. These materials may be organic in nature or mineral. They may also be categorised as "collected material" and "self-secreted material".[17]
Collected materials
Some animals collect materials with plastic properties which are used to construct and shape the nest. These include resin collected by stingless bees, mud collected by swallows and silk collected by hummingbirds.[17]
Some materials in nature act as ready made "building blocks" to the animals in question, such as feathers and leaf petioles for some birds and animal
An animal builder may collect a variety of materials and use them in complex ways to form useful habitat. The nest of the
About the construction of nest by the long-tailed tit, it has been written:
"...the most amazing thing about it (the building behaviour) is, in my opinion that so few, so simple and so rigid movements together lead to the construction of so superb a result."
Material of animal origin
Birds form the majority of the group of animals which collect building material of animal origin. They collect animal fur and feathers of other species of birds to line their nests. Almost 56% of all families of passerine birds have species which utilise spider silk. Most birds use spider silk as in the case of the long-tailed tit, previously discussed; however the little spiderhunter (Arachnothera longirostra) of Asian tropical forests uses spider silk differently. It constructs a nest of plant strips which it suspends below a large leaf using spider silk for about a 150 or so of "pop-rivets".[21]
Plant material
Flowering plants provide a variety of resources – twigs, leaves, petioles, roots, flowers and seeds. Basal plants, such as lichens, mosses and ferns also find use in structures built by animals. The leaves of grasses and palms being elongate and parallel-veined are very commonly used for building. These, along with palm fibers and horse-hair fern are used to build hanging baskets. Wooden twigs form the greater proportion of materials used in the nests of large birds. Plants and trees not only provide resources but also sites. Branches provide support in the form of cantilevered beams while leaves and green twigs provide flexible but strong supports.[17]
Structures formed from plant material include beaver dams, which are constructed by foraged branches and sticks.[22] The dam is a wall of sticks constructed on a moving water source, which forces the water to collect in one area and to stop flowing.[22] Beavers begin to build a dam in an area where rocks and other debris slow the flow of the water. The beavers then form a small platform of sticks stretching across the water source.[22] More sticks and branches are added to build the dam up over time.[22] The structure in the center of the dam, known as the lodge, serves as a home for the beavers and protects them from predators.[22] The primary reason behind the construction of beaver dams is to surround the lodge with deep water, which protects the beaver from land-dwelling predators.[22] The entrance of the dam is underwater to prevent predators such as bears and wolves from entering, and the sticks at the top of the lodge are not packed tightly, which allows air into the structure.[22]
Mud and stones
Mud is used by a few species of a wide variety of families including wasps and birds. Mud is
Self-secreted materials
The majority of self-secreted materials are produced by insects and selection acts on this characteristic of production of self-secreting materials and increases the fitness of the animal. In some cases, the self-secreted material is directly applied, as in the case of ecribellate silk, spun by
Cocoons are another type of structure formed to protect the organism from predation.[22] In order to transform from a larva into a butterfly or moth, a caterpillar must undergo drastic changes in its body. These changes require significant amounts of energy and occur over long periods of time, making a caterpillar very vulnerable to predation.[22] To overcome this, caterpillars will produce silk to form a cocoon or pupa, a structure in which the caterpillar will reside while pupating to lower its risk of predation.[22] Some species of caterpillar, such as the silkworm (Bombyx mori) are able to spin multiple cocoons in the event that one gets destroyed.[22] Other caterpillars will even form defensive structures to accompany their pupas.[22] The Aethria carnicauda caterpillar uses the hairs that cover its body as a defensive mechanism against predators.[22] When it is time to form a cocoon, the caterpillar rips the hairs off of its body and places them around the pupating site.[22] This creates a series of defensive walls to protect the vulnerable caterpillar while resides in its cocoon.[22]
Evolutionary consequences
Recently, some researchers have argued that the structures built by animals affect the evolution of the constructor, a phenomenon known as niche construction.
See also
- Tool use by non-human animals
- Nest-building in primates
References
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- ^ Chaboo, C.S., S. Adam, K. Nishida, L. Schletzbaum. 2023. Architecture, construction, retention, and repair of fecal shields in three tribes of tortoise beetles (Insecta: Coleoptera: Chrysomelidae Cassidinae: Cassidini, Mesomphaliini, Spilophorini). ZooKeys Special Issue, Research on Chrysomelidae 9. ZooKeys 1177: 87–146. DOI: 10.3897/zookeys.1177.102600.