What are Symbiotic Relationships?

In simple terms, symbiosis is defined as interaction between two biological species. These interactions are generally long-lasting. The term is derived from the Greek words, syn meaning with and biosis meaning living and was coined by the German biologist Heinrich Anton de Bary in the year 1879.

He used the term to define the coexistence of two dissimilar living organisms. While earlier symbiotic relationships were generally defined as those relationships that were mutually beneficial, the actual term is a little clouded today in its definition. It is widely used to describe biological interactions between many different species.

These relationships may be of different types. A study of biology will tell you that the main types are mutualistic, commensalism, and parasitism. There are some symbiotic relationships, wherein the two species are completely dependent on each other for survival, there are other relationships that are formed only for certain necessities.

Other than the three main forms, these relationships can also be classified as ectosymbiotic (wherein one organism, like barnacles live on another organism like the baleen whales), or endosymbiotic (wherein one organism, for example lactobacilli, lives inside another organism like human beings).

Symbiotic relationships can also be classified as obligate, where in the relationship is essential for the life of at least one of the organisms or facultative, that is where the relationship is beneficial to the organisms, but not essential for survival.

The three main forms of symbiotic relationships that we have mentioned earlier in the article have been discussed ahead.

Many people tend to use the terms mutualism and symbiosis interchangeably, but that is actually incorrect. Mutualism is just a type of biological interaction in which the two species that have a relationship, derive benefits from each other.

Symbiosis, on the other hand, is a broad category that includes different forms of biological interactions between species. Mutualism within a species is more often termed as cooperation. Mutualism is extremely important in ecology and without these relationships, the terrestrial ecosystem may be vastly disturbed.

Almost 70% of the organisms that are a part of the terrestrial ecosystem rely on the mycorrhizal relationships that they share with fungi. Mutualism is also an important driving factor for both the biological diversity that we see today and the co-evolution. One of the best examples of mutualism is the one that exists between sea anemones and anemone fish.

The sea anemones are responsible to provide fish with protection from predators that cannot bear the stings on the tentacles of anemones and the fish on the other hand protect the sea anemones from butterfly fish which feed on anemones.

Commensalism in another form of symbiotic relationships, wherein the biological interaction that the two species share, one derives benefits but the other remains largely unaffected and is not benefited or harmed by the relationship. The term commensalism comes from the Latin phrase cum mensa, which literally translates to sharing a table.

It was this phrase that gave birth to the English word commensal, which is the root of the term commensalism. It is difficult to find examples of commensalism, as it is less seen in nature and it is difficult to prove whether or not the animal is affected by the guest.

Two examples of commensalism given in this article will help you understand this phenomenon better. Egrets and livestock have a relationship that can be largely defined as commensalism.

When cattle graze on the field, their motion results in the flying of insects which cattle egrets following the livestock, feed on. While the egrets benefit from this interaction, the cattle remain unaffected in any manner.

Parasitism is another form in which amongst the two species, which have a biological interaction, one benefits but the other is harmed. It has been noticed in parasitic relationships that the parasites are much smaller than the host. Parasites tend to affect the fitness levels of the host in many ways.

They generally live on the hosts in need of food or shelter or even as a contagious medium. Those parasites that live on the surface of the host are called ectoparasites and those that live inside the host's body are called endoparasites. Endoparasites can be intercellular or intracellular. An epiparasite is a type of parasite that eats other parasites.

One of the best examples of parasitism is the relationship between vertebrate hosts and organisms like tapeworms and fleas.

Whether a terrestrial ecosystem or an aquatic ecosystem, symbiotic relationships are extremely important for the survival of several species, While sometimes mutually beneficial and on other occasions a cause of harm to one of the species, without these relationships, severe havoc may be caused with the existing ecological system.