biological associations / relationships in living organisms

          biological associations / relationships in living organisms   plant animal ecology

  1. Symbiosis:
    This is derived from a Greek word which simply means ‘living together’ and can be utilized to explain any association that exist between two organisms.
  2. Mutualism:
    This can be used to describe an association between two organisms and where both organisms seemingly benefit from each other.

  3. Commensalism:
    This is a type of association where one organism known as the commensal benefits, and the other known as the host is seemingly unaffected. In ecology, commensalism is a type of relationship between two organisms where one organism benefits but the other is neutral.

There is no harm or benefit to the neutral organism. Commensalism is derived from the English word commensal, meaning “sharing of food” in human social interaction, which was in turn derived from the Latin cum mensa, meaning “sharing a table”

Examples of Commensal Relationships

Commensalism is much more difficult to exhibit than parasitism and mutualism, for it is simpler to show a single example where the host is affected, than it is to demonstrate or invalidate that possibility.

Cattle Egrets and Livestock

An example of commensalism is cattle egrets pasturing in fields together with cattle or other livestock. As cattle, horses, and other livestock graze on the field, their movements stir up different types of insects which are being fed on by the cattle egrets.

The egrets benefit from this relationship due to the fact that the livestock have assisted them to discover their foods while the livestock are characteristically not affected by it.

Tigers and Golden Jackals

In India, one golden jackals barred from their pack have been found to be forming commensal relationships with tigers.


  1. Parasitism
    This is the type of association where one organism known as the the parasite benefits, while the other known as the host is negatively affected, injured, weakened, sickened or killed. An example of parasitism is the association between the parasitic tapeworms and the vertebrate hosts.

This type of association would as well suit the relationship that exists between a carnivore and its live prey and herbivore and the plant it feeds on, particularly if they are extremely specialized in the food they eat.

Parasites are usually defined as organisms that cannot survive without their host and which have unique modifications to their body or their life cycle for this association. In a lot ways though, the variation that exists between a lion eating a gazelle and a flea feeding on a dog, is an issue of relative size.

A lot of sea slugs have evolved close relationships with other organisms. Solar Powered Sea Slugs is another rather different group of relationships that have been discovered with sea slugs. This relationship involves plants and plant organelles.

A group, the herbivorous sacoglossan sea slugs keep chloroplasts and other plant plastids alive from the plants they consume and make use of the sugars they synthesize from photosynthesis for their own nutrition.

Conventionally, parasite is used to describe organisms that are visible to the naked eye, or macroparasites like the protozoa andhelminths. Parasite currently includes microparasites, which are generally smaller, like viruses and bacteria.

A few examples of parasites include the plants mistletoe and cuscuta, and animals like the hookworms.

As opposed to predators, parasites do not kill their host. They are usually much smaller than their host, and will frequently live in or on their host for an extensive period. Both the parasite and the predator are particular instances of consumer-resource interactions.

Parasites exhibit a high degree of specialization, and replicate at a faster rate than their hosts.

Parasites diminish host biological fitness by common or dedicated pathology, like parasitic castration and mutilation of secondary sex characteristics, to the modification of host behavior.

Parasites increase their fitness by exploiting hosts for resources necessary for their survival, e.g. food, water, heat, habitat, and transmission. Although parasitism applies unmistakably to a lot of cases, it is part of a range of types of interactions that exist between species, instead of the exclusive category.

In a lot of cases, it is not easy to illustrate that the host is harmed. In others, there may be no obvious specialization on the part of the parasite, or the interaction that exists between the organisms may be momentary.

Types of parasitic relationship between organisms

Parasites are classified based on their interactions with their hosts and on their life cycles. An obligate parasite is completely reliant on the host to complete its life cycle, while a facultative parasite is not.

Human head lice (Pediculus humanus capitis) are ectoparasites. Parasites that live on the surface of the host are known as ectoparasites . Example-mites. The parasites that live inside the host are known as endo-parasites which as well include parasitic worms.

Endoparasites can survive in one of two forms: intercellular parasites ie parasites that inhabit spaces in the host’s body or intracellular parasites ie parasites that inhabit cells in the host’s body.

Intracellular parasites, like protozoa, bacteria or viruses, have a propensity of depending on a third organism, which is commonly referred to as the carrier or vector. The vector does the function of transmitting them to the host.

An instance of this interaction is the spread of malaria, caused by a protozoan of the genus Plasmodium, to humans by the bite of an anopheline mosquito. Those parasites living in an intermediary position, being half-ectoparasites and half-endoparasites, are every now and then called mesoparasite.

An epiparasite is a parasite that feeds on another parasite. This relationship is as well occasionally known as hyperparasitism. An example is exhibited by a protozoan (the hyperparasite) inhabiting the digestive tract of a flea living on a dog.

Social parasites take advantage of interactions that exists among members of social organisms like ants or termites. An instance is Phengaris arion, a butterfly whose larvae make use of mimicry to parasitize definite species of ants.

In kleptoparasitism, parasites share food obtained by the host. An instance is the brood parasitism practiced by cuckoos and cowbirds, which do not construct nests of their own and leave their eggs in nests of other species.

The host acts as a “babysitter” as they raise the young as their own. If the host takes away the cuckoo’s eggs, a few cuckoos will come again and attack the nest to force host birds to remain subject to this parasitic association.

Author: TheGoldendiamond

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