Predator

predator (borrowed from Latin praedātor, from praedor → “loot, pillage”, from praeda → “booty, spoils, prey”) is any animal or other organism that hunts and kills other non-plant organisms (their prey), primarily for food.

Predator classification

Predators can be classified, either by the type of food consumed (trophic level classification), or by how they access nutrient resources (functional classification).

Classification by trophic levels

Classification by trophic levels is based on the concept of food chains. The main types of food chains are those of predators, parasites and saprophytes. As far as the predator chain is concerned, it is based on producer organisms, capable of obtaining nourishment through the transformation of inorganic substances or through the absorption of solar energy.

They are the nutritional source of the primary consumers, the herbivores; those who feed on other animals are the secondary consumers. Secondary consumers are called carnivores. Above the secondary consumers there may be tertiary consumers, who feed on other carnivores, and so on. However, because the energy input that is passed to the next levels is gradually less, this predatory hierarchy must be limited and rarely reaches the fifth or sixth level. The way it is formed, there will be one predator that will rank at the top of the food chain; these are the so-called primary predators, or absolute predators.

Even if a primary predator is at the top of the food chain, it is possible that by removing it from its ecosystem and moving it to another, it loses its predominant position and can change from predator to prey. For the usual principle it is possible that an organism that is typically classified as prey, can become a primary predator, if it is placed in a different environment. Many organisms (first and foremost humans) can feed by tapping into multiple levels of the food chain, making classification problematic.

Organisms that behave as both carnivores and herbivores are called omnivores. There are also saprophytes, organisms that feed on animal or plant organic matter in an advanced state of decomposition. The existence of food relationships between the various groups of organisms belonging to the same food chain means that an animal species can not increase indefinitely in number at the expense of another: it establishes a biological balance between the organisms that inhabit the same environment.

Functional classification

This system aims to classify predators based on the way they obtain nutrient resources and the natural interaction between prey and predator. According to this type of classification, four groups of predators are formed:

True predators: those who kill their prey for the purpose of feeding on it. These types of predators may actively hunt their prey, or camouflage themselves with the environment, waiting for an opportune time to attack. Many predators tend to maul their prey, such as the lion or leopard; others, such as some types of snakes, eat it whole. There are also some types of predators that, in order to render their prey harmless, inject them with venom. In many cases, such as the rattlesnake or some types of spider, the venom is also important during the digestion phase. In other cases, prey die directly in the mouth, or in the digestive system of the predator organism, as happens for example to plankton ingested by cetaceans.

Grazers: grazers include all mobile consumers of plant prey or sessile marine organisms, such as bryozoans. Grazing organisms may kill their prey, but this is a very rare case, which can be found in the consumption of phytoplankton by zooplankton. Usually grazers feed on plants; livestock may pull the roots out of the grass, but usually the plant is eaten at the top, allowing it to regrow.

Parasites: with parasite we can identify an organism that during a part or the totality of its existence lives at the expense of another, damaging it without causing immediate death during direct contact. They can range from the macroscopic mistletoe, a plant parasite, to microscopic parasites such as cholera. Some parasites are often difficult to distinguish from grazers, so much so that phytophagous organisms can be considered parasitic (such as many insects that are considered plant pests). Their feeding habits are similar in many respects, however they differ in the close association they have with their host organisms. Often very strong parasitic relationships can be formed, so much so that hosts may have only one parasitic organism accompanying them for life.

Parasitoids: parasitoid organisms are organisms that live on or in their host and draw nourishment directly from it. They have a behavior on one hand similar to parasites and on the other to carnivores, as their host does not die immediately but is slowly consumed, in order to allow the survival of the parasitoid. Unlike parasites, therefore, the fate of their hosts is, inevitably, death. An example of a parasitoid organism is given by the ichneumon wasp. It lays its eggs inside another species. Its larvae feed on the host from the inside, not causing great damage at first, but in the long run they eat the internal organs, until the destruction of the nervous system and, subsequently, the death of the prey, which will happen when the larvae will have reached full maturity.

Degree of specialization

Some predators develop a high degree of specialization, leading them to hunt a single species of prey. Others are more opportunistic and can eat anything. Predators that develop a specialization towards a particular prey develop strategies that make it easier for them to hunt. Similarly, prey develop methods to more easily escape natural predators. In this way, the balance between the population that hunts and the population that is hunted is indirectly maintained.

Some predators specialize in a class of prey, rather than a single species. In this way they may change prey types when the preferred target is extremely scarce, allowing the usually preyed upon species to increase its population.

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