Definition of Biological Interaction

All species on earth, from bacteria to humans, are part of an ecosystem, and as such, all are related in some way to other species. Interspecific interactions are those established between organisms of different species that coexist. These interactions can be of various types, depending on how they affect each species involved.

Ecosystems are complex networks of relationships between all its components: living beings and elements of the physical environment. Ecosystems are not, as can sometimes be thought, collections of species that inhabit one place. determined, but rather the relationships that are established between them and with the physical environment that define the ecosystem.

Negative interactions: predation, parasitism and competition

The relationships in which only one of the two participants benefits, are called parasitism if the affected organism does not die during the relationship and predation, if one of the two organisms dies (because it is eaten by the other).

The predation It occurs when one species (predator) feeds on another (prey), causing its death. Predation is a negative interaction for the prey and a positive one for the predator, since this is how it obtains its food.

For example, the lion preys on the zebra, and the eagle preys on the mouse. Predatory relationships are also established between herbivores and plants (being the plants the ones that are preyed on, although we commonly have more in mind the dramatic images of lioness hunts from wildlife documentaries).

Parasitism occurs when a species (parasite) lives at the expense of another (Guest), causing harm or illness. The parasite benefits from the host's resources, but does not kill it.

The most common type of parasitism is when the parasite obtains its food from the host's fluids, or tissues, and lives in or on it. This is the case, for example, of dog fleas and ticks that feed on blood and live on the dog or tapeworms and roundworms, intestinal parasites of humans (and many other species of mammals).

In parasitism, the parasite does not directly kill the host to eat it, because if the host dies the parasite also dies, but it can cause the host weakness or disease, and a massive infection can cause the death of the host.

There are organisms that parasites seem to not affect at all. Certain fish harbor a parasite in their oral cavity that feeds on their mucosa. When it enters the fish's mouth, it attaches itself to its tongue and begins to feed on the blood vessels in the tongue.

Over time, the fish loses its tongue and the parasite replaces it with its own body. From this moment, the fish can use the parasite as its own language and not only does it not affect them at all, but if the parasite is removed, the fish dies.

This type of relationship would not be completely within the framework of parasitism, because although the parasite feeds of the fish and cannot live outside of it, the fish, once it has lost its tongue, also depends on the parasite to continue alive.

There is other types of parasitism lesser known, such as brood parasitism of certain birds, such as the thrush.

Adult thrushes lay their eggs in the nest of other birds, which will raise the young thrushes as their own. Thrush chicks are often larger than their foster parents' chicks, and end up hogging all the food their parents bring them.

The competence It is observed when two or more species use the same limited resource, such as food, space or light. Competition reduces the availability of the resource for both species and may affect their survival and reproduction. For example, plants compete for water and nutrients in the soil, and carnivorous animals compete for prey.

Neutral interactions: commensalism

Commensalism occurs when a species (diner) benefits from the relationship with another (host), without affecting or benefiting her. Commensalism is an interaction that is positive for the diner and neutral for the host.

For example, the woodpecker uses the hollow of a tree as a refuge, without harming the tree. Or the African vultures, which feed on the remains of the lions' food. The vulture benefits from an activity of the lions, but the lions are not harmed, since the vulture waits for the lions to finish to eat the remains and does not steal their food.

Positive Interactions: Mutualism

There are relationships in which both species benefit, and are known as mutualism. Mutualism is a positive interaction for both species, as it allows them to obtain resources or services that they could not obtain on their own.

For example, the bee and the flower benefit from mutualism: the bee gets nectar and pollen from the flower, and the flower gets pollination from the bee.

Clownfish keep sea anemones clean, and in return, gain protection by hiding in their poisonous tentacles. Anemone venom does not affect clownfish, but it does affect their predators, so the fish gets excellent protection.

The case of the parasite that replaces the tongue of fish, after a initial stage of parasitism, where the fish loses its tongue, evolves into a stage of mutualism, where both species benefit mutually: the fish gets a new tongue and the parasite gets food.

Mutualistic interactions are highly varied, and cooperation is as powerful an evolutionary force as competition in shaping the ecosystem.

The degree of dependency of mutualistic species can range from helping each other, such as the clownfish and anemone, which are perfectly capable of living apart, to a greater dependence, as in the case of plants, which depend on pollinating insects to reproduce, or the fish without a tongue that depends on its parasite to feed.

The lichens, Which are a association of a fungus and an alga, and while some species of lichen-forming fungi can live separate from their algae, it is very rare to find them that way.

The alga, which is photosynthetic, provides carbohydrates to the fungus, and this helps to keep the algal cells moist, which have less tolerance for dryness. The lichen can survive in environments where neither the alga nor the fungus could survive on its own.

These are some of the types of interactions between species in an ecosystem, but there are many more. These interactions influence the structure and functioning of ecosystems, as well as the evolution and adaptation of species.