![Hagfish Slime Predator Deterrence](https://upload.wikimedia.org/wikipedia/commons/f/f9/Hagfish_Slime_Predator_Deterrence.jpg)
Anti-predator adaptations are mechanisms developed through
evolution
Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...
that assist
prey
Predation is a biological interaction where 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 ...
organisms in their constant struggle against
predator
Predation is a biological interaction where 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 th ...
s. Throughout the animal kingdom, adaptations have evolved for every stage of this struggle, namely by avoiding detection, warding off attack, fighting back, or escaping when caught.
The first line of defence consists in avoiding detection, through mechanisms such as
camouflage
Camouflage is the use of any combination of materials, coloration, or illumination for concealment, either by making animals or objects hard to see, or by disguising them as something else. Examples include the leopard's spotted coat, the b ...
,
masquerade,
apostatic selection
Apostatic selection is a form of negative frequency-dependent selection. It describes the survival of individual prey animals that are different (through mutation) from their species in a way that makes it more likely for them to be ignored by the ...
, living underground, or
nocturnality.
Alternatively, prey animals may ward off attack, whether by advertising the presence of strong defences in
aposematism, by
mimicking animals which do possess such defences, by
startling the attacker, by
signalling to the predator that pursuit is not worthwhile, by
distraction
Distraction is the process of diverting the attention of an individual or group from a desired area of focus and thereby blocking or diminishing the reception of desired information. Distraction is caused by: the lack of ability to pay attentio ...
, by using defensive structures such as spines, and by
living in a group. Members of groups are at
reduced risk of predation, despite the increased conspicuousness of a group, through improved vigilance, predator confusion, and the likelihood that the predator will attack some other individual.
Some prey species are capable of fighting back against predators, whether
with chemicals, through
communal defence, or by ejecting noxious materials. Many animals can escape by fleeing rapidly, outrunning or outmanoeuvring their attacker.
Finally, some species are able to escape even when caught by
sacrificing certain body parts: crabs can shed a claw, while lizards can shed their tails, often distracting predators long enough to permit the prey to escape.
Avoiding detection
Staying out of sight
![Seychelles Fruit Bat - Pteropus seychellensis](https://upload.wikimedia.org/wikipedia/commons/7/73/Seychelles_Fruit_Bat_-_Pteropus_seychellensis.jpg)
Animals may avoid becoming prey by living out of sight of predators, whether
in caves,
burrows, or by being
nocturnal.
Nocturnality is an animal behavior characterized by activity during the night and sleeping during the day. This is a behavioral form of detection avoidance called crypsis used by animals to either avoid predation or to enhance prey hunting. Predation risk has long been recognized as critical in shaping behavioral decisions. For example, this predation risk is of prime importance in determining the time of evening emergence in echolocating bats
Bats are mammals of the order Chiroptera.''cheir'', "hand" and πτερόν''pteron'', "wing". With their forelimbs adapted as wings, they are the only mammals capable of true and sustained flight. Bats are more agile in flight than most bir ...
. Although early access during brighter times permits easier foraging, it also leads to a higher predation risk from bat hawk
The bat hawk (''Macheiramphus alcinus'') is a raptor found in sub-Saharan Africa and south Asia to New Guinea. It is named for its diet, which consists mainly of bats. It requires open space in which to hunt, but will live anywhere from dense r ...
s and bat falcon
The bat falcon (''Falco rufigularis'') is a falcon that is a resident breeder in tropical Mexico, Central and South America, Trinidad. It was long known as ''Falco albigularis''; the names ''Falco fusco-coerulescens'' or ''Falco fuscocaerulesce ...
s. This results in an optimum evening emergence time that is a compromise between the conflicting demands. Another nocturnal adaptation can be seen in kangaroo rat
Kangaroo rats, small mostly nocturnal rodents of genus ''Dipodomys'', are native to arid areas of western North America. The common name derives from their bipedal form. They hop in a manner similar to the much larger kangaroo, but developed t ...
s. They forage in relatively open habitats, and reduce their activity outside their nest burrows in response to moonlight. During a full moon, they shift their activity towards areas of relatively dense cover to compensate for the extra brightness.
Camouflage
Camouflage
Camouflage is the use of any combination of materials, coloration, or illumination for concealment, either by making animals or objects hard to see, or by disguising them as something else. Examples include the leopard's spotted coat, the b ...
uses any combination of materials, coloration, or illumination for concealment to make the organism hard to detect by sight. It is common in both terrestrial and marine animals. Camouflage can be achieved in many different ways, such as through resemblance to surroundings, disruptive coloration
Disruptive coloration (also known as disruptive camouflage or disruptive patterning) is a form of camouflage that works by breaking up the outlines of an animal, soldier or military vehicle with a strongly contrasting pattern. It is often comb ...
, shadow elimination by countershading
Countershading, or Thayer's law, is a method of camouflage in which an animal's coloration is darker on the top or upper side and lighter on the underside of the body. This pattern is found in many species of mammals, reptiles, birds, fish, a ...
or counter-illumination
Counter-illumination is a method of active camouflage seen in marine animals such as firefly squid and midshipman fish, and in military prototypes, producing light to match their backgrounds in both brightness and wavelength.
Marine animals of ...
, self-decoration, cryptic behavior, or changeable skin patterns and colour. Animals such as the flat-tail horned lizard of North America have evolved to eliminate their shadow and blend in with the ground. The bodies of these lizards are flattened, and their sides thin towards the edge. This body form, along with the white scales fringed along their sides, allows the lizards to effectively hide their shadows. In addition, these lizards hide any remaining shadows by pressing their bodies to the ground.
Masquerade
Animals can hide in plain sight by masquerading as inedible objects. For example, the potoo
Potoos (family Nyctibiidae) are a group of birds related to the nightjars and frogmouths. They are sometimes called poor-me-ones, after their haunting calls. The family Nyctibiidae was formerly included with the nightjars in the order Caprim ...
, a South American bird, habitually perches on a tree, convincingly resembling a broken stump of a branch, while a butterfly, ''Kallima
''Kallima'', known as the oakleaf or oak leaf butterflies, is a genus of butterflies of the subfamily Nymphalinae in the family Nymphalidae. They are found in east, south and southeast Asia. Their common name is a reference to the lower surface ...
'', looks just like a dead leaf.
Apostatic selection
Another way to remain unattacked in plain sight is to look different from other members of the same species. Predators such as tits selectively hunt for abundant types of insect, ignoring less common types that were present, forming search images of the desired prey. This creates a mechanism for negative frequency-dependent selection Frequency-dependent selection is an evolutionary process by which the fitness of a phenotype or genotype depends on the phenotype or genotype composition of a given population.
* In positive frequency-dependent selection, the fitness of a phenotyp ...
, apostatic selection
Apostatic selection is a form of negative frequency-dependent selection. It describes the survival of individual prey animals that are different (through mutation) from their species in a way that makes it more likely for them to be ignored by the ...
.
Warding off attack
Many species make use of behavioral strategies to deter predators.
Startling the predator
Many weakly-defended animals, including moth
Moths are a paraphyletic group of insects that includes all members of the order Lepidoptera that are not butterflies, with moths making up the vast majority of the order. There are thought to be approximately 160,000 species of moth, many of w ...
s, butterflies, mantises
Mantises are an order (Mantodea) of insects that contains over 2,400 species in about 460 genera in 33 families. The largest family is the Mantidae ("mantids"). Mantises are distributed worldwide in temperate and tropical habitats. They hav ...
, phasmids, and cephalopods such as octopuses, make use of patterns of threatening or startling behaviour, such as suddenly displaying conspicuous eyespots, so as to scare off or momentarily distract a predator, thus giving the prey animal an opportunity to escape. In the absence of toxins or other defences, this is essentially bluffing, in contrast to aposematism which involves honest signals.
Pursuit-deterrent signals
Pursuit-deterrent signals are behavioral signals used by prey to convince predators not to pursue them. For example, gazelle
A gazelle is one of many antelope species in the genus ''Gazella'' . This article also deals with the seven species included in two further genera, '' Eudorcas'' and '' Nanger'', which were formerly considered subgenera of ''Gazella''. A third ...
s stot, jumping high with stiff legs and an arched back. This is thought to signal to predators that they have a high level of fitness and can outrun the predator. As a result, predators may choose to pursue a different prey that is less likely to outrun them.
White-tailed deer
The white-tailed deer (''Odocoileus virginianus''), also known as the whitetail or Virginia deer, is a medium-sized deer native to North America, Central America, and South America as far south as Peru and Bolivia. It has also been introduced t ...
and other prey mammals flag with conspicuous (often black and white) tail markings when alarmed, informing the predator that it has been detected.
Warning calls given by birds such as the Eurasian jay are similarly honest signal
Within evolutionary biology, signalling theory is a body of theoretical work examining communication between individuals, both within species and across species. The central question is when organisms with conflicting interests, such as in sex ...
s, benefiting both predator and prey: the predator is informed that it has been detected and might as well save time and energy by giving up the chase, while the prey is protected from attack.
Playing dead
Another pursuit-deterrent signal is thanatosis or playing dead. Thanatosis is a form of bluff in which an animal mimics its own dead body, feigning death to avoid being attacked by predators seeking live prey. Thanatosis can also be used by the predator in order to lure prey into approaching.
An example of this is seen in white-tailed deer
The white-tailed deer (''Odocoileus virginianus''), also known as the whitetail or Virginia deer, is a medium-sized deer native to North America, Central America, and South America as far south as Peru and Bolivia. It has also been introduced t ...
fawns, which experience a drop in heart rate in response to approaching predators. This response, referred to as "alarm bradycardia", causes the fawn's heart rate to drop from 155 to 38 beats per minute within one beat of the heart. This drop in heart rate can last up to two minutes, causing the fawn to experience a depressed breathing rate and decrease in movement, called tonic immobility. Tonic immobility is a reflex response that causes the fawn to enter a low body position that simulates the position of a corpse. Upon discovery of the fawn, the predator loses interest in the "dead" prey. Other symptoms of alarm bradycardia, such as salivation, urination, and defecation, can also cause the predator to lose interest.
Distraction
Marine molluscs such as sea hare
The clade Anaspidea, commonly known as sea hares ('' Aplysia'' species and related genera), are medium-sized to very large opisthobranch gastropod molluscs with a soft internal shell made of protein. These are marine gastropod molluscs in the ...
s, cuttlefish, squid and octopuses give themselves a last chance to escape by distracting their attackers. To do this, they eject a mixture of chemicals, which may mimic food or otherwise confuse predators. In response to a predator, animals in these groups release ink
Ink is a gel, sol, or solution that contains at least one colorant, such as a dye or pigment, and is used to color a surface to produce an image, text, or design. Ink is used for drawing or writing with a pen, brush, reed pen, or quill. Thicker ...
, creating a cloud, and opaline, affecting the predator's feeding senses, causing it to attack the cloud.
Distraction display
Distraction displays, also known as diversionary displays, or paratrepsis are anti-predator behaviors used to attract the attention of an enemy away from something, typically the nest or young, that is being protected by a parent. Distraction disp ...
s attract the attention of predators away from an object, typically the nest or young, that is being protected, as when some birds feign a broken wing while hopping about on the ground.
Mimicry and aposematism
Mimicry occurs when an organism (the mimic) simulates signal properties of another organism (the model) to confuse a third organism. This results in the mimic gaining protection, food, and mating advantages. There are two classical types of defensive mimicry: Batesian and Müllerian. Both involve aposematic
Aposematism is the advertising by an animal to potential predators that it is not worth attacking or eating. This unprofitability may consist of any defences which make the prey difficult to kill and eat, such as toxicity, venom, foul taste o ...
coloration, or warning signals, to avoid being attacked by a predator.[
In Batesian mimicry, a palatable, harmless prey species mimics the appearance of another species that is noxious to predators, thus reducing the mimic's risk of attack.] This form of mimicry is seen in many insect
Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three ...
s. The idea behind Batesian mimicry is that predators that have tried to eat the unpalatable species learn to associate its colors and markings with an unpleasant taste. This results in the predator learning to avoid species displaying similar colours and markings, including Batesian mimics, which are in effect parasitic on the chemical or other defences of the unprofitable models. Some species of octopus can mimic a selection of other animals by changing their skin color, skin pattern and body motion. When a damselfish attacks an octopus, the octopus mimics a banded sea-snake. The model chosen varies with the octopus's predator and habitat. Most of these octopuses use Batesian mimicry, selecting an organism repulsive to predators as a model.
In Müllerian mimicry
Müllerian mimicry is a natural phenomenon in which two or more well-defended species, often foul-tasting and sharing common predators, have come to mimic each other's honest warning signals, to their mutual benefit. The benefit to Mülleria ...
, two or more aposematic forms share the same warning signals,[ as in ]viceroy
A viceroy () is an official who reigns over a polity in the name of and as the representative of the monarch of the territory. The term derives from the Latin prefix ''vice-'', meaning "in the place of" and the French word ''roy'', meaning " ...
and monarch butterflies
The monarch butterfly or simply monarch (''Danaus plexippus'') is a milkweed butterfly (subfamily Danainae) in the family Nymphalidae. Other common names, depending on region, include milkweed, common tiger, wanderer, and black-veined brown. ...
. Birds avoid eating both species because their wing patterns honestly signal their unpleasant taste.
Defensive structures
Many animals are protected against predators with armour in the form of hard shells (such as most molluscs and turtles
Turtles are an order of reptiles known as Testudines, characterized by a special shell developed mainly from their ribs. Modern turtles are divided into two major groups, the Pleurodira (side necked turtles) and Cryptodira (hidden necked tur ...
), leathery or scaly skin (as in reptiles), or tough chitinous exoskeletons (as in arthropod
Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chiti ...
s).
A spine is a sharp, needle-like structure used to inflict pain on predators. An example of this seen in nature is in the Sohal surgeonfish. These fish have a sharp scalpel-like spine on the front of each of their tail fins, able to inflict deep wounds. The area around the spines is often brightly colored to advertise the defensive capability; predators often avoid the Sohal surgeonfish. Defensive spines may be detachable, barbed or poisonous. Porcupine spines are long, stiff, break at the tip, and are barbed to stick into a would-be predator. In contrast, the hedgehog
A hedgehog is a spiny mammal of the subfamily Erinaceinae, in the eulipotyphlan family Erinaceidae. There are seventeen species of hedgehog in five genera found throughout parts of Europe, Asia, and Africa, and in New Zealand by introductio ...
's short spines, which are modified hairs, readily bend, and are barbed into the body, so they are not easily lost; they may be jabbed at an attacker.
Many species of slug caterpillar, Limacodidae
The Limacodidae or Eucleidae are a family of moths in the superfamily Zygaenoidea or the Cossoidea;Scoble, M.J. (1992). ''The Lepidoptera: Form, Function and Diversity.'' Oxford University Press. the placement is in dispute. They are often c ...
, have numerous protuberances and stinging spines along their dorsal surfaces. Species that possess these stinging spines suffer less predation than larvae that lack them, and a predator, the paper wasp
Paper wasps are vespid wasps that gather fibers from dead wood and plant stems, which they mix with saliva, and use to construct nests made of gray or brown papery material. Some types of paper wasps are also sometimes called umbrella wasps, d ...
, chooses larvae without spines when given a choice.
Safety in numbers
Group living can decrease the risk of predation to the individual in a variety of ways, as described below.
Dilution effect
A dilution effect is seen when animals living in a group "dilute" their risk of attack, each individual being just one of many in the group. George C. Williams and W.D. Hamilton
William Donald Hamilton (1 August 1936 – 7 March 2000) was a British evolutionary biologist, recognised as one of the most significant evolutionary theorists of the 20th century.
Hamilton became known for his theoretical work expounding a ...
proposed that group living evolved because it provides benefits to the individual rather than to the group as a whole, which becomes more conspicuous as it becomes larger. One common example is the shoaling
In biology, any group of fish that stay together for social reasons are shoaling, and if the group is swimming in the same direction in a coordinated manner, they are schooling. In common usage, the terms are sometimes used rather loosely. Ab ...
of fish. Experiments provide direct evidence for the decrease in individual attack rate seen with group living, for example in Camargue horse
The Camargue horse is an ancient breed of horse indigenous to the Camargue area in southern France. Its origins remain relatively unknown, although it is generally considered one of the oldest breeds of horses in the world. For centuries, ...
s in Southern France. The horse-fly
Horse-flies or horseflies are true flies in the family Tabanidae in the insect order Diptera. They are often large and agile in flight, and only the female horseflies bite animals, including humans, to obtain blood. They prefer to fly in su ...
often attacks these horses, sucking blood and carrying diseases. When the flies are most numerous, the horses gather in large groups, and individuals are indeed attacked less frequently. Water striders
The Gerridae are a family of insects in the order Hemiptera, commonly known as water striders, water skeeters, water scooters, water bugs, pond skaters, water skippers, or water skimmers. Consistent with the classification of the Gerridae as tr ...
are insects that live on the surface of fresh water, and are attacked from beneath by predatory fish. Experiments varying the group size of the water striders showed that the attack rate per individual water strider decreases as group size increases.
Selfish herd
The selfish herd theory was proposed by W.D. Hamilton
William Donald Hamilton (1 August 1936 – 7 March 2000) was a British evolutionary biologist, recognised as one of the most significant evolutionary theorists of the 20th century.
Hamilton became known for his theoretical work expounding a ...
to explain why animals seek central positions in a group. The theory's central idea is to reduce the individual's domain of danger. A domain of danger is the area within the group in which the individual is more likely to be attacked by a predator. The center of the group has the lowest domain of danger, so animals are predicted to strive constantly to gain this position. Testing Hamilton's selfish herd effect, Alta De Vos and Justin O'Rainn (2010) studied brown fur seal
The brown fur seal (''Arctocephalus pusillus''), also known as the Cape fur seal, South African fur seal and Australian fur seal, is a species of fur seal.
Description
The brown fur seal is the largest and most robust member of the fur seal ...
predation from great white shark
The great white shark (''Carcharodon carcharias''), also known as the white shark, white pointer, or simply great white, is a species of large Lamniformes, mackerel shark which can be found in the coastal surface waters of all the major ocean ...
s. Using decoy seals, the researchers varied the distance between the decoys to produce different domains of danger. The seals with a greater domain of danger had an increased risk of shark attack.
Predator satiation
A radical strategy for avoiding predators which may otherwise kill a large majority of the emerging stage of a population is to emerge very rarely, at irregular intervals. Predators with a life-cycle of one or a few years are unable to reproduce rapidly enough in response to such an emergence. Predators may feast on the emerging population, but are unable to consume more than a fraction of the brief surfeit of prey. Periodical cicadas, which emerge at intervals of 13 or 17 years, are often used as an example of this predator satiation
Predator satiation (less commonly called predator saturation) is an anti-predator adaptation in which prey briefly occur at high population density, population densities, reducing the probability of an individual organism being eaten.
When predati ...
, though other explanations of their unusual life-cycle have been proposed.
Alarm calls
Animals that live in groups often give alarm calls
In animal communication, an alarm signal is an antipredator adaptation in the form of Signalling theory, signals emitted by social animals in response to danger. Many primates and birds have elaborate alarm calls for warning Biological specific ...
that give warning of an attack. For example, vervet monkey
The vervet monkey (''Chlorocebus pygerythrus''), or simply vervet, is an Old World monkey of the family Cercopithecidae native to Africa. The term "vervet" is also used to refer to all the members of the genus ''Chlorocebus''. The five distinct ...
s give different calls depending on the nature of the attack: for an eagle
Eagle is the common name for many large birds of prey of the family Accipitridae. Eagles belong to several groups of genera, some of which are closely related. Most of the 68 species of eagle are from Eurasia and Africa. Outside this area, j ...
, a disyllabic cough; for a leopard or other cat, a loud bark; for a python
Python may refer to:
Snakes
* Pythonidae, a family of nonvenomous snakes found in Africa, Asia, and Australia
** ''Python'' (genus), a genus of Pythonidae found in Africa and Asia
* Python (mythology), a mythical serpent
Computing
* Python (pro ...
or other snake, a "chutter". The monkeys hearing these calls respond defensively, but differently in each case: to the eagle call, they look up and run into cover; to the leopard call, they run up into the trees; to the snake call, they stand on two legs and look around for snakes, and on seeing the snake, they sometimes mob it. Similar calls are found in other species of monkey, while birds also give different calls that elicit different responses.
Improved vigilance
In the improved vigilance effect, groups are able to detect predators sooner than solitary individuals. For many predators, success depends on surprise. If the prey is alerted early in an attack, they have an improved chance of escape. For example, wood pigeon flocks are preyed upon by goshawk
Goshawk may refer to several species of birds of prey, mainly in the genus ''Accipiter'':
* Northern goshawk, ''Accipiter gentilis'', often referred to simply as the goshawk, since it is the only goshawk found in much of its range (in Europe and N ...
s. Goshawks are less successful when attacking larger flocks of wood pigeons than they are when attacking smaller flocks. This is because the larger the flock size, the more likely it is that one bird will notice the hawk sooner and fly away. Once one pigeon flies off in alarm, the rest of the pigeons follow. Wild ostrich
Ostriches are large flightless birds of the genus ''Struthio'' in the order Struthioniformes, part of the infra-class Palaeognathae, a diverse group of flightless birds also known as ratites that includes the emus, rheas, and kiwis. There ...
es in Tsavo National Park in Kenya feed either alone or in groups of up to four birds. They are subject to predation by lions. As the ostrich group size increases, the frequency at which each individual raises its head to look for predators decreases. Because ostriches are able to run at speeds that exceed those of lions for great distances, lions try to attack an ostrich when its head is down. By grouping, the ostriches present the lions with greater difficulty in determining how long the ostriches' heads stay down. Thus, although individual vigilance decreases, the overall vigilance of the group increases.
Predator confusion
Individuals living in large groups may be safer from attack because the predator may be confused by the large group size. As the group moves, the predator has greater difficulty targeting an individual prey animal. The zebra
Zebras (, ) (subgenus ''Hippotigris'') are African equines with distinctive black-and-white striped coats. There are three living species: the Grévy's zebra (''Equus grevyi''), plains zebra (''E. quagga''), and the mountain zebra (''E. zebr ...
has been suggested by the zoologist Martin Stevens and his colleagues as an example of this. When stationary, a single zebra stands out because of its large size. To reduce the risk of attack, zebras often travel in herds. The striped patterns of all the zebras in the herd may confuse the predator, making it harder for the predator to focus in on an individual zebra. Furthermore, when moving rapidly, the zebra stripes create a confusing, flickering motion dazzle
Camouflage is the use of any combination of materials, coloration, or illumination for concealment, either by making animals or objects hard to see, or by disguising them as something else. Examples include the leopard's spotted coat, the b ...
effect in the eye of the predator.
Fighting back
Defensive structures such as spines may be used both to ward off attack as already mentioned, and if need be to fight back against a predator. Methods of fighting back include chemical defences, mobbing,[ defensive regurgitation,] and suicidal altruism.
Chemical defences
Many prey animals, and to defend against seed predation
Seed predation, often referred to as granivory, is a type of plant-animal interaction in which granivores (seed predators) feed on the seeds of plants as a main or exclusive food source,Hulme, P.E. and Benkman, C.W. (2002) "Granivory", pp. 13 ...
also seeds of plants, make use of poisonous chemicals for self-defence. These may be concentrated in surface structures such as spines or glands, giving an attacker a taste of the chemicals before it actually bites or swallows the prey animal: many toxins are bitter-tasting. A last-ditch defence is for the animal's flesh itself to be toxic, as in the puffer fish
Tetraodontidae is a family of primarily marine and estuarine fish of the order Tetraodontiformes. The family includes many familiar species variously called pufferfish, puffers, balloonfish, blowfish, blowies, bubblefish, globefish, swellfish ...
, danaid butterflies and burnet moth
The Zygaenidae moths are a family of Lepidoptera. The majority of zygaenids are tropical, but they are nevertheless quite well represented in temperate regions. Some of the 1000 or so species are commonly known as burnet or forester moths, oft ...
s. Many insects acquire toxins from their food plants; ''Danaus'' caterpillars accumulate toxic cardenolides
A cardenolide is a type of steroid. Many plants contain derivatives, collectively known as cardenolides, including many in the form of cardenolide glycosides (cardenolides that contain structural groups derived from sugars). Cardenolide glycoside ...
from milkweeds ( Asclepiadaceae).
Some prey animals are able to eject noxious materials to deter predators actively. The bombardier beetle has specialized glands on the tip of its abdomen that allows it to direct a toxic spray towards predators. The spray is generated explosively through oxidation of hydroquinones and is sprayed at a temperature of 100 °C. Armoured crickets similarly release blood at their joints when threatened ( autohaemorrhaging). Several species of grasshopper including '' Poecilocerus pictus'', ''Parasanaa donovani
''Parasanaa'' is a genus of bush-cricket recorded from India, Indochina, Malesia through to New Guinea. It is represented by a single species, ''Parasanaa donovani''Beier (1944) ''Stett. Entomol. Z.'' 105: 89.
This insect has also been called '' ...
'',[ '']Aularches miliaris
''Aularches miliaris'' is a grasshopper species of the monotypic genus ''Aularches'', belonging to the family Pyrgomorphidae.(2013''Aularches miliaris'' (Linnaeus, 1758) from Orthoptera Species File (OSF) Online. (retrieved 16 March 2020). The ...
'',[ and '']Tegra novaehollandiae
''Tegra novaehollandiae'' is a species of bush crickets in the tribe Cymatomerini and the subfamily Pseudophyllinae; it is native to tropical Asia.
R. W. G. Hingston (1927), The liquid-squirting habit of oriental grasshoppers'. Transactions of ...
'' secrete noxious liquids when threatened, sometimes ejecting these forcefully.[ ]Spitting cobra
A spitting cobra is any of several species of cobras that can defensively spray a toxic secretion - functioning as both a venom (that can be injected via a wound) and a toxungen (that can be sprayed on the target surface) - from their fangs in ...
s accurately squirt venom from their fangs at the eyes of potential predators, striking their target eight times out of ten, and causing severe pain. Termite soldiers in the Nasutitermitinae
The Nasutitermitinae are a subfamily of higher termites that includes more than 80 genera. They are most recognisable by the more highly derived soldier caste which exhibits vestigial mandibles and a protruding fontanellar process on the head ...
have a fontanellar gun
The fontanellar gun is a defense mechanism in the form of a horn-like frontal projection (''nasus'') on the head of the soldier caste which is capable of expelling chemical weaponry at a distance, a trait exclusive to the subfamily Nasutitermitina ...
, a gland on the front of their head which can secrete and shoot an accurate jet of resinous terpene
Terpenes () are a class of natural products consisting of compounds with the formula (C5H8)n for n > 1. Comprising more than 30,000 compounds, these unsaturated hydrocarbons are produced predominantly by plants, particularly conifers. Terpenes ...
s "many centimeters". The material is sticky and toxic to other insects. One of the terpenes in the secretion, pinene
Pinene is a collection of unsaturated bicyclic monoterpenes. Two geometric isomers of pinene are found in nature, α-pinene and β-pinene. Both are chiral. As the name suggests, pinenes are found in pines. Specifically, pinene is the major comp ...
, functions as an alarm pheromone
A 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 like hormones outside the body of the secreting individual, to affect the behavi ...
. Seeds deter predation with combinations of toxic non-protein amino acid
Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha a ...
s, cyanogenic glycoside
In chemistry, a glycoside is a molecule in which a sugar is bound to another functional group via a glycosidic bond. Glycosides play numerous important roles in living organisms. Many plants store chemicals in the form of inactive glycosides. ...
s, protease
A protease (also called a peptidase, proteinase, or proteolytic enzyme) is an enzyme that catalyzes (increases reaction rate or "speeds up") proteolysis, breaking down proteins into smaller polypeptides or single amino acids, and spurring the ...
and amylase inhibitors, and phytohemagglutinins.[
A few vertebrate species such as the ]Texas horned lizard
The Texas horned lizard (''Phrynosoma cornutum'') is one of about 14 North American species of spikey-bodied reptiles called horned lizards, all belonging the genus '' Phrynosoma''. It occurs in south-central regions of the US and northeastern M ...
are able to shoot squirts of blood from their eyes, by rapidly increasing the blood pressure within the eye sockets, if threatened. Because an individual may lose up to 53% of blood in a single squirt, this is only used against persistent predators like foxes, wolves and coyotes ( Canidae), as a last defence. Canids often drop horned lizards after being squirted, and attempt to wipe or shake the blood out of their mouths, suggesting that the fluid has a foul taste; they choose other lizards if given the choice, suggesting a learned aversion towards horned lizards as prey.[
The slime glands along the body of the ]hagfish
Hagfish, of the class Myxini (also known as Hyperotreti) and order Myxiniformes , are eel-shaped, slime-producing marine fish (occasionally called slime eels). They are the only known living animals that have a skull but no vertebral column, ...
secrete enormous amounts of mucus when it is provoked or stressed. The gelatinous slime has dramatic effects on the flow and viscosity of water, rapidly clogging the gills of any fish that attempt to capture hagfish; predators typically release the hagfish within seconds ''(pictured above)''. Common predators of hagfish include seabirds, pinnipeds and cetaceans, but few fish, suggesting that predatory fish avoid hagfish as prey.
Communal defence
In communal defence, prey groups actively defend themselves by grouping together, and sometimes by attacking or mobbing a predator, rather than allowing themselves to be passive victims of predation. Mobbing
Mobbing, as a sociological term, means bullying of an individual by a group, in any context, such as a family, peer group, school, workplace, neighborhood, community, or online. When it occurs as physical and emotional abuse in the workplace, suc ...
is the harassing of a predator by many prey animals. Mobbing is usually done to protect the young in social colonies. For example, red colobus
Red colobuses are Old World monkeys of the genus ''Piliocolobus''. It was formerly considered a subgenus within the genus ''Procolobus'', which is now restricted to the olive colobus. They are closely related to the black-and-white colobus monke ...
monkeys exhibit mobbing when threatened by chimpanzees
The chimpanzee (''Pan troglodytes''), also known as simply the chimp, is a species of great ape native to the forest and savannah of tropical Africa. It has four confirmed subspecies and a fifth proposed subspecies. When its close relative th ...
, a common predator. The male red colobus monkeys group together and place themselves between predators and the group's females and juveniles. The males jump together and actively bite the chimpanzees. Fieldfares are birds which may nest either solitarily or in colonies. Within colonies, fieldfares mob and defecate on approaching predators, shown experimentally to reduce predation levels.
Defensive regurgitation
Some birds and insects use defensive regurgitation to ward off predators. The northern fulmar
The northern fulmar (''Fulmarus glacialis''), fulmar, or Arctic fulmar is a highly abundant seabird found primarily in subarctic regions of the North Atlantic and North Pacific oceans. There has been one confirmed sighting in the Southern Hem ...
vomits a bright orange, oily substance called stomach oil when threatened. The stomach oil is made from their aquatic diets. It causes the predator's feathers to mat, leading to the loss of flying ability and the loss of water repellency. This is especially dangerous for aquatic birds because their water repellent feathers protect them from hypothermia
Hypothermia is defined as a body core temperature below in humans. Symptoms depend on the temperature. In mild hypothermia, there is shivering and mental confusion. In moderate hypothermia, shivering stops and confusion increases. In severe ...
when diving for food.
European roller
The European roller (''Coracias garrulus'') is the only member of the roller family of birds to breed in Europe. Its overall range extends into the Middle East, Central Asia and the Maghreb.
The European roller is found in a wide variety of hab ...
chicks vomit a bright orange, foul smelling liquid when they sense danger. This repels prospective predators and may alert their parents to danger: they respond by delaying their return.
Numerous insects utilize defensive regurgitation. The eastern tent caterpillar
The eastern tent caterpillar (''Malacosoma americanum'') is a species of moth in the family Lasiocampidae, the tent caterpillars or lappet moths. It is univoltine, producing one generation per year. It is a tent caterpillar, a social species th ...
regurgitates a droplet of digestive fluid to repel attacking ants. Similarly, larvae of the noctuid moth
The Noctuidae, commonly known as owlet moths, cutworms or armyworms, are a family of moths. They are considered the most controversial family in the superfamily Noctuoidea because many of the clades are constantly changing, along with the other f ...
regurgitate when disturbed by ants. The vomit of noctuid moths has repellent and irritant properties that help to deter predator attacks.
Suicidal altruism
An unusual type of predator deterrence is observed in the Malaysian exploding ant. Social hymenoptera rely on altruism to protect the entire colony, so the self-destructive acts benefit all individuals in the colony. When a worker ant's leg is grasped, it suicidally expels the contents of its hypertrophied submandibular glands, expelling corrosive irritant compounds and adhesives onto the predator. These prevent predation and serve as a signal to other enemy ants to stop predation of the rest of the colony.
Escaping
Flight
The normal reaction of a prey animal to an attacking predator is to flee by any available means, whether flying, gliding, falling, swimming, running, jumping, burrowing
An Eastern chipmunk at the entrance of its burrow
A burrow is a hole or tunnel excavated into the ground by an animal to construct a space suitable for habitation or temporary refuge, or as a byproduct of locomotion. Burrows provide a form of s ...
or rolling
Rolling is a type of motion that combines rotation (commonly, of an axially symmetric object) and translation of that object with respect to a surface (either one or the other moves), such that, if ideal conditions exist, the two are in contact ...
, according to the animal's capabilities. Escape paths are often erratic, making it difficult for the predator to predict which way the prey will go next: for example, birds such as snipe
A snipe is any of about 26 wading bird species in three genera in the family Scolopacidae. They are characterized by a very long, slender bill, eyes placed high on the head, and cryptic/ camouflaging plumage. The ''Gallinago'' snipes have a ...
, ptarmigan
''Lagopus'' is a small genus of birds in the grouse subfamily commonly known as ptarmigans (). The genus contains three living species with numerous described subspecies, all living in tundra or cold upland areas.
Taxonomy and etymology
The ge ...
and black-headed gull
The black-headed gull (''Chroicocephalus ridibundus'') is a small gull that breeds in much of the Palearctic including Europe and also in coastal eastern Canada. Most of the population is migratory and winters further south, but some birds r ...
s evade fast raptors such as peregrine falcons with zigzagging or jinking flight. In the tropical rain forests of Southeast Asia in particular, many vertebrates escape predators by falling and gliding.[ Among the insects, many moths turn sharply, fall, or perform a powered dive in response to the sonar clicks of bats. Among fish, the stickleback follows a zigzagging path, often doubling back erratically, when chased by a fish-eating ]merganser
''Mergus'' is the genus of the typical mergansers , fish-eating ducks in the subfamily Anatinae. The genus name is a Latin word used by Pliny the Elder and other Roman authors to refer to an unspecified waterbird.
The common merganser (''Mer ...
duck.
Autotomy
Some animals are capable of autotomy
Autotomy (from the Greek ''auto-'', "self-" and ''tome'', "severing", αὐτοτομία) or self-amputation, is the behaviour whereby an animal sheds or discards one or more of its own appendages, usually as a self-defense mechanism to elude ...
(self-amputation), shedding one of their own appendages in a last-ditch attempt to elude a predator's grasp or to distract the predator and thereby allow escape. The lost body part may be regenerated later. Certain sea slug
Sea slug is a common name for some marine invertebrates with varying levels of resemblance to terrestrial slugs. Most creatures known as sea slugs are gastropods, i.e. they are sea snails (marine gastropod mollusks) that over evolutionary time ...
s discard stinging papillae; arthropods such as crabs can sacrifice a claw, which can be regrown over several successive moults; among vertebrate
Vertebrates () comprise all animal taxa within the subphylum Vertebrata () (chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with c ...
s, many geckos and other lizards shed their tails when attacked: the tail goes on writhing for a while, distracting the predator, and giving the lizard time to escape; a smaller tail slowly regrows.
History of observations
Aristotle
Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher and polymath during the Classical period in Ancient Greece. Taught by Plato, he was the founder of the Peripatetic school of ph ...
recorded observations (around 350 BC) of the antipredator behaviour of cephalopods in his ''History of Animals
''History of Animals'' ( grc-gre, Τῶν περὶ τὰ ζῷα ἱστοριῶν, ''Ton peri ta zoia historion'', "Inquiries on Animals"; la, Historia Animalium, "History of Animals") is one of the major texts on biology by the ancient Gr ...
'', including the use of ink as a distraction, camouflage, and signalling.
In 1940, Hugh Cott
Hugh Bamford Cott (6 July 1900 – 18 April 1987) was a British zoologist, an authority on both natural and military camouflage, and a scientific illustrator and photographer. Many of his field studies took place in Africa, where he was espec ...
wrote a compendious study of camouflage, mimicry, and aposematism, ''Adaptive Coloration in Animals
''Adaptive Coloration in Animals'' is a 500-page textbook about camouflage, warning coloration and mimicry by the Cambridge zoologist Hugh Cott, first published during the Second World War in 1940; the book sold widely and made him famous.
The ...
''.
By the 21st century, adaptation to life in cities
A city is a human settlement of notable size.Goodall, B. (1987) ''The Penguin Dictionary of Human Geography''. London: Penguin.Kuper, A. and Kuper, J., eds (1996) ''The Social Science Encyclopedia''. 2nd edition. London: Routledge. It can be def ...
had markedly reduced the antipredator responses of animals such as rats and pigeons; similar changes are observed in captive and domesticated
Domestication is a sustained multi-generational relationship in which humans assume a significant degree of control over the reproduction and care of another group of organisms to secure a more predictable supply of resources from that group. A ...
animals.
See also
*
*
References
Sources
*
*
*
*
External links
Antipredatory Behavior lecture by William E. Cooper
{{evo ecol
Ethology
Evolution
Predation