Predation

Predation is a type of interaction in which one organism uses another organism of a different species as a food source. This is referred to as prey in both the animal and plant kingdoms. Through predation, predators are able to play a key role in the food chain, keeping prey populations in check and aiding evolutionary drive, leading to the development of anti-predatory adaptations.

More narrowly, and more properly, it applies to animals (predators) that kill and consume all or most of other individually captured animals (prey); in a more general sense it applies to the consuming relationship between animals, including filtration (for aquatic organisms that feed on plankton) but not parasitism; in an even broader sense the term is sometimes used as a synonym for food relationship, including in this case also parasitism, in which an organism feeds on parts of the host, and the food relationship between herbivores and plants, in which the plant can be consumed in part (as in parasitism) or entirely (as more properly in predation); in fact from the ecological point of view there is a functional identity in the relationship between any pair of organisms of which one feeds on the other. Predation between individuals of the same species is called cannibalism.

Ecology

The predation relationship characterizes all trophic levels of a food chain above the first level of consumption, represented by herbivorous organisms. Predation is thus one of the main mechanisms by which ecosystem energy, stored in the form of animal food, is distributed to higher trophic levels.

In terms of adaptive “strategy,” it differs fundamentally from parasitism in that the survival of predator populations is based on the withdrawal of life from the prey population, while the survival of parasites is generally based on the survival of the host population; as the saying goes, the subsistence of predators is based on the consumption of capital (which, however, is constantly replenished through reproduction), while that of parasites is based on the consumption of interest.

Despite this, especially when the forms of parasitism are harmful to the hosts and impair their ability to survive and reproduce, possibly leading them to death, the two relationships have some points in common, especially with regard to the dynamics of their respective populations. Sometimes there is evidence that predators are controlling agents of prey populations, which they would prevent from overproliferating, sometimes it appears that predator populations are controlled by the size of prey populations.

In cases where a predator depends on a single or few prey species, such as the polar fox, which in Arctic regions feeds almost exclusively on lemmings and rabbits, marked fluctuations in prey and predator populations can occur and influence each other: in particularly favorable years, in fact, rodents may experience population explosions that will invariably allow the foxes to successfully rear more offspring, from which will result in an increase in the fox population; as a consequence, in the following year(s) the rate of predation on rodents will increase and their populations will decline; this in turn will cause a reduction in the number of predators, and so on.

Conversely, when a predator feeds on many different prey items, the populations of prey and predators are maintained in a state of relative numerical equilibrium in which the drawdown carried out by predators does not exceed the limit that would drive prey populations into decline and eventually extinction, which would result in the extinction of the predators themselves.

In conclusion, predation is a mechanism whose effect is to maintain animal populations within optimal numerical levels, such, that is, not to exceed the “carrying capacity” of the habitat; also contributes to the “health status” of populations, on the one hand by eliminating the weakest individuals, because older or younger or sick, from the populations of prey, on the other hand allowing survival only to the strongest and most capable individuals of the populations of predators.

Ethology

Predation behaviors are extremely varied: some predators use several hunting systems, usually adapted to overcome the defenses of different prey, others are specialized in only one system; some, moreover, hunt individually, others in groups, aggregating among conspecifics, sometimes in highly organized social formations, or with individuals of other species. Depending on the case, sight, hearing, smell, or touch, or more than one sense, provide the appropriate stimuli to lead the predator to prey.

A rather general system of hunting consists in exploring the habitat frequented by the prey in order to flush out some of them or to surprise them in the open; a number of animals practice this system, such as some octopuses, birds, mammals, etc.; the octopusOctopus is the most common of these. the octopus Octopus cyanea, for example, proceeds to successive leaps between rocks and bushes of algae, which wraps with tentacles, in which it is likely that nest prey, these are blocked by the sudden action of the octopus and extracted from hiding; cuttlefish and some fish throw jets of water on the sand of the bottom, eventually exposing animals that nest there; several birds similar to storks proceed slowly in the turbid water of flooded land, probing it continuously with their half-open beak that they close again as soon as they perceive contact with prey; A similar system is used by some birds and some fish, which adopt as “beaters” other animals (not necessarily predators) whose presence wreaks havoc on their prey; for example, tanagers often associate with marching columns of legionary ants, at the passage of which a myriad of insects fly off in disorder, and the Cattle Egret and even a dragonfly (Brachythemis leucosticta) follow herds of grazing herbivores, capturing insects disturbed by them.

The surprise technique is typically used by predators whose speed and endurance in running are exceeded by those of prey; This includes both the stealthy approach, in which the predator approaches the prey without provoking alarm reactions, and involves a silent action, often discontinuous, a non-directed path of approach to the prey to take advantage of shelters and is associated with cryptic characteristics of the predator (for example Felidae), and the ambush, in which the predator, also usually cryptic and sheltered, waits motionless for the prey to come within range.

Some ambush predators sometimes use systems to attract prey, such as appendages that mimic animals on which prey feeds (e.g., anglerfish, alligator turtle, etc.) or position themselves so that they can see prey in contrast against a bright background (Fish, Birds) or use traps that facilitate prey capture (e.g., spider webs, ant colonies, etc.).

Highly mobile and more evolved ambush predators (usually Vertebrates) are often able to learn the locations most frequented by prey and wait for them there; others (including some fish) that practice this method of hunting exclusively move periodically if prey is scarce. Deception, consisting of the masking of one’s identity or intentions, is a widely used expedient for approaching prey; the predator can in this case have the features of a species harmless to the prey (aggressive camouflage) or show disinterest for the prey, moving close to it quietly (so do the rats, when they try to capture small birds, but also other species) or keep closely attached to a species whose presence does not alarm the prey, as do some fish of the Aulostomiformes and Fistularidae that disguise their silhouette “riding” parrotfish or groupers.

An interesting fact is that man intentionally uses camouflage for the purpose of predation either by masking himself with skins of animals whose presence does not alarm prey or by using fake baits that imitate animals attractive to them. The pursuit hunt, mainly practiced by Fishes, Birds and Mammals, can be preceded by approach maneuvers, and it is based either on the speed of the predator (for example Fishes, Birds, Felids) or on its resistance (for example Canids, Hyenids); the speed is not necessarily the maximum possible, but it can be greatly accelerated in the moments immediately preceding the capture through the protrusion of the mouth (Fishes) or of the legs (birds of prey), etc.

Canids and Hyenids, less well equipped than Felids to capture prey and kill it quickly, tire it out by prolonged pursuit, which is also valuable in separating weaker prey from a pack. Some predatory Fishes, Birds and Mammals are able to intercept the prey by following a shorter path that coincides with the one followed by it, that is, cutting it off, or, if the prey is stationary, they direct the attack not directly on it but in the direction in which it presumably will direct the escape, at least in appearance showing the ability to predict this from the head-tail orientation of the prey. Some, finally, are also able to assess the possible escape routes of the prey and lurk in those or attack it from those.

In predation understood as the capture and killing of prey for food, many predators (especially invertebrates and lower vertebrates) probably act on predominantly instinctual responses (pursuit and capture) but instinct and learning, especially among Birds and Mammals, are largely integrated; the pursuit response is probably instinctive and generally appears at an early age, when youngsters, motivated rather by play than driven by hunger, sprint against, and attempt the capture of anything that moves, but hunting techniques, both individual and herd, are completely mastered after a more or less long period of apprenticeship in which the young first follow and observe their mother or the adult members of the herd (learning by imitation), then take an active part in the hunt, putting into practice what they have learned by imitation and discarding all the “wrong” moves, that is, those that lead to failure (learning by trial and error).

However, learning by trial and error also plays a role in less evolved animals, at least as far as the recognition of the “quality” of prey is concerned, whether edible or not (even some Amphibians are able to discard, after some trials, potential prey that they have experienced as disgusting or having effective means of active defense). The most evolved predators (Birds and Mammals) are certainly able to learn the features of prey and it is likely that some of them are able to form “images of research”, ie mental representations of prey which are looking for and perception of which show to react with particular readiness.

Adaptations and behavior

Predation can be summarized in a maximum of four phases: the search for prey, the attack, the capture and finally the consumption. The relationship that is created between prey and predator is obviously to the advantage of the latter. However, predation often brings significant evolutionary advantages in the predated species, maximizing their chance of nourishment and making them have a better chance of surviving a predator attack. One example of these adaptations is camouflage, a mechanism whereby organisms have an appearance that helps them hide from their surroundings. Camouflage consists not only of colors, but also the form in which the organism presents itself.

Another form of adaptation can be seen in camouflage, a phenomenon whereby an organism shows itself to be similar to another species. A typical example is that of Eristalis tenax, whose appearance is similar to that of the common house bee. This type of mimicry, which is used exclusively as a defense against predators, is called Batesian mimicry.

However, some predators may use a form of camouflage in order to approach prey. Female fireflies of the genus Photuris, for example, copy the light signals of other species and use them to attract prey to themselves.

Aposematism is a form of defense that is completely opposite to mimicry. Animals that use this device are characterized by bright colors on a more or less extensive part of the body, so that they are easily recognizable by possible predators. Often aposematic animals are poisonous, or simply have an unpleasant taste. It is precisely the peculiarity of the colors that characterize it that makes the predator turn away, making him fear for his safety.

When predation is successful, it brings an energy gain. However, hunting inevitably reduces a predator’s energy resources, which is why predators usually decide not to attack, as long as the energy costs would outweigh the benefits. Group hunting allows predators, such as lions, hyenas, wolves and piranhas, to feed effectively, reducing the energy dissipated during hunting. Another type of predatory selection is one that causes predators to preferentially hunt prey of a certain size to the exclusion of others. Prey too large would be too difficult to catch, those too small would not provide the right energy supply.

This form of predation is closely correlated with the size of the predator and its possible prey. In this way, adult elephants will be avoided by lions, although the young represent vulnerable prey. It could also be seen that, often, some captive pets can make a distinction between animals that cohabit in the same human area versus wild animals that are outside their area, and may be considered prey. This can lead to a kind of peaceful coexistence between two species normally linked by the predator-prey relationship. This kind of behavior tends to be explained through a series of mutual advantages, or through fear of the reaction of the masters.

Anti-predator adaptations

Aggression

Predatory animals often use their usual forms of attack as a defense against possible predators. The electrophorus, or electric eel, uses electricity both to kill its prey and to keep predators away, causing them to prefer other targets. Many animals that are not true predators also develop forms of defense, to try to resist the attack of their natural predators. Zebras, for example, can unleash powerful kicks that can go so far as to kill those struck, while other animals resort to attacks with tusks or horns.

Mobbing

Mobbing is a kind of group attack on a predator. Mobbing is a typical behavior of birds, although it can be seen in a variety of animal species. Usually, the first bird to spot the predator makes a cry of alarm, called a mobbing-call. The birds are in this way recalled and warned of the presence of the predator, which then no longer has the opportunity to act by surprise, after which the group begins to attack and harass him with vocalizations and direct attacks, with the aim to distract and confuse him. However direct attacks are very rare. It is possible that birds, even of different species, respond to mobbing-call.

Mobbing-call, in addition to attracting other birds, puts the performer of the call at a disadvantage, causing it to be noticed by the predator, and thus become possible prey. In spite of everything, the advantages of mobbing are remarkable and range from the possibility of safeguarding nests, drawing attention to a single individual, to the effective protection from predators, intimidated by this form of mass attack.

Warnings

Warnings serve to demotivate the predator to attack the prey. When the gazelles see a possible predator, they begin to run slowly making large jumps, performing what is called stotting. By doing so, they communicate to the predator that it has been spotted, and that its chances of success are diminished. The predators then, often give up hunting, having understood that from that moment it is no longer profitable.

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