Predation

Predation is a type of interaction in which one organism uses another organism of a different species as a food source. It is called predation in both the animal and plant kingdoms. Through predation, predators are able to play a key role in the food chain, keeping the prey population in check and promoting the evolutionary drive that leads 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.

The ecological role of predators is remarkable, as they maintain biodiversity and prevent any single species from becoming dominant. Many predators are known as keystone species and are able to keep a particular ecosystem in balance. The introduction or removal of these predators causes a shift in population balances and densities, which can lead to serious imbalances.

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 its adaptive “strategy”, it differs fundamentally from parasitism in the fact that the survival of predator populations is based on the extraction of vines from the prey population, whereas the survival of parasites is generally based on the survival of the host population; as it is said, the subsistence of predators is based on the consumption of capital (which, however, is constantly replenished by reproduction), whereas that of parasites is based on the consumption of interest. Nevertheless, especially when the forms of parasitism are detrimental to the hosts, impairing their ability to survive and reproduce, and possibly leading to their 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 control prey populations, which they would prevent from overpopulating; sometimes it appears that predator populations are controlled by the size of prey populations. In cases where a predator is dependent on one or a few prey species, such as the arctic fox, which feeds almost exclusively on lemmings and rabbits in Arctic regions, pronounced numerical fluctuations in prey and predator populations can occur and influence each other: In particularly good years, the rodent population may explode, allowing the foxes to successfully raise more offspring, leading to an increase in the fox population; as a result, in the following year or years, the predation rate on rodents will increase and their population will decrease, leading to a decrease in the number of predators, and so on.

On the other hand, when a predator feeds on many different prey species, the populations of prey and predators are maintained in a state of relative numerical equilibrium, in which the removal by predators does not exceed the limit that would drive prey populations into decline and eventual extinction, which would result in the extinction of the predators themselves.

In conclusion, predation is a mechanism whose effect is to maintain animal populations at optimal numerical levels, that is, not exceeding the “carrying capacity” of the habitat; it also contributes to the “health status” of populations, on the one hand by eliminating weaker individuals, because they are older or younger or sicker, from prey populations, and on the other hand by allowing only the strongest and most capable individuals in predator populations to survive.

Ethology

Predator behavior is extremely diverse: some predators use multiple hunting systems, usually adapted to overcome the defenses of different prey; others specialize in only one system; some also 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 the prey. A more general system of hunting consists of exploring the habitat frequented by the prey in order to flush some out or surprise them in the open; a number of animals, such as some octopuses, birds, mammals, etc., practice this system.

The octopus cyanea, for example, moves in successive jumps between rocks and tufts of seaweed, which it wraps with its tentacles, where prey may be lurking; the sudden action of the octopus blocks the prey and brings it out of hiding; Cuttlefish and some fish throw jets of water onto the bottom sand, possibly exposing nesting animals; several stork-like birds move slowly through the murky water of the flooded ground, constantly probing it with their half-open beaks, which they snap shut as soon as they sense contact with prey; a similar system is used by some birds and some fish, which adopt as “hitters” other animals (not necessarily predators) whose presence causes havoc with their prey; for example, tanagers often associate with marching columns of legion ants, at whose passage a myriad of insects fly haphazardly, and the heron’s guardabuoi and even a dragonfly (Brachythemis leucosticta) follow herds of grazing herbivores, capturing insects disturbed by them.

The surprise technique is generally used by predators whose speed and endurance exceed those of the prey; it includes both stealth approach, in which the predator approaches the prey without provoking its alarm reactions and involves a silent, often discontinuous action, an undirected path of approach to the prey to take advantage of shelter and is associated with cryptic characteristics of the predator (e.g., Felidae), and ambush, in which the predator, also usually cryptic and sheltered, waits motionlessly for the prey to come within range.

Some ambush predators sometimes use prey-calling systems, such as appendages that mimic animals on which the prey feeds (e.g., anglerfish, alligator turtle, etc.), or position themselves so that the prey can be seen in contrast to a bright background (fish, birds), or use traps that facilitate prey capture (e.g., spider webs, ant mounds, etc.). Highly mobile and evolved ambush predators (usually vertebrates) are often able to learn the most frequented places of prey and wait for them there; others (including some fish) that exclusively practice this hunting method move periodically when prey is scarce.

Deception, which consists of concealing one’s identity or intentions, is a widely used means of approaching prey; In this case, the predator may take on the characteristics of a species that is harmless to the prey (aggressive camouflage), or show disinterest in the prey by approaching it quietly (as rats do when trying to catch small birds, but also other species), or even stay close to a species whose presence does not alarm the prey, as in the case of certain fishes of the Aulostomiformes and Fistularidae that disguise their silhouette by “riding” on parrotfish or groupers.

Interestingly, humans deliberately use camouflage for predation, either by covering themselves with animal skins whose presence does not alarm prey, or by using false baits that mimic animals that are attractive to them. Pursuit hunting, practiced mainly by fishes, birds and mammals, may be preceded by approach maneuvers and is based either on the speed of the predator (e.g., fishes, birds, Felidae) or on its resistance (e.g., canids, hyenids); the speed is not necessarily the maximum possible, but can be greatly accelerated in the moments immediately before capture by protruding the mouth (fishes) or legs (birds of prey), etc.

Canids and hyenids, less well equipped than Felidae to capture and kill prey quickly, tire prey by prolonged pursuit, which is also valuable in separating weaker prey from a pack. Some predatory fish, birds, and mammals are able to intercept prey by following a shorter path that collides with the one it is following, i.e., cutting it off, or, if the prey is stationary, directing the attack not directly at it but in the direction in which it will presumably turn its flight, at least in appearance, showing the ability to predict this from the head-tail orientation of the prey. Finally, some are able to estimate the prey’s possible escape routes and lurk in them or attack from them.

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 in birds and mammals, are largely integrated; The chase response is probably instinctive and usually appears early in life, when young, motivated by play rather than hunger, sprints against anything that moves and attempts to capture it, but hunting techniques, But hunting techniques, both individual and herd, are fully mastered after a longer or shorter period of apprenticeship, during which the young first follow and observe the mother or 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 certain role in less evolved animals, at least in terms of recognizing the “quality” of prey, whether edible or not (even some amphibians are able to discard, after a few trials, potential prey that they have experienced as disgusting or that have effective means of active defense). The more evolved predators (birds and mammals) are certainly capable of learning the characteristics of prey, and it is likely that some of them are able to form “search images”, i.e. mental representations of the prey they are looking for, to the perception of which they show a particular readiness to respond.

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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