Parasitism:

When an organism benefits at the expense of other organism it is referred as parasitism. Parasitism is a type of ecological relationship which behaves like symbionts. They are smaller in size, i.e. most of the parasites are smaller than the host. Ultimately it reduces the biological fitness of host. It is much different from Parasitoidism. Parasitoidism is a type of relationship which eventually kills the host. They harm the fitness by changing their natural behavior, changing secondary sexual characteristics of the host and infecting the host. Parasites just utilize the host for their food, shelter, growth factors and nutrients. In medicines, humans are parasites except microorganisms.

Types of Parasites

Depending on the habitat of parasites, they are classified as follows.

• Ectoparasites: When parasites sustain on the surface of the host they are referred to as ectoparasites.
• Endoparasites: When parasites sustain inside the host they are referred to as endoparasites. They can exist in two below mentioned forms.

                 Intercellular endoparasites: It lives in the host organism space like bacteria and virus

                 Intracellular endoparasites: It lives in the host organisms cells

• Epiparasites: A parasite which lives on another parasite.
• Hyper parasites: Protozoan living in the digestive tract of the dog.
• Social parasites: Parasites is benefited by interacting with social organisms like ants and termites.
• Parasitoids: The larval development is either in or out of the host organism, resulting in the death of the host. Parasitoid behaves much more similar to predators.

Distribution of Parasites

Diversity of parasites is different from free living organisms. Depending on the assemblage of parasites with different hosts they are diversified with terminology as follows.

• Infra population:   When a single species of all parasites reside in single host it is referred as infra population.
• Meta population: When a single species of all parasites reside in host population it is referred as Meta population.
• Infra community: When all species of all parasites reside in single host it is referred as Infra community.
• Component community: When all species of all parasites reside in host population it is referred as component community.
• Compound community: When all species of all parasites reside in all host species of an ecosystem it is referred as compound community.

Parasitic Evolution

In due course of time of evolution, biotrophic evolution of parasite took place. Every organism life cycle includes atleast one or more parasites. Parasites are abundant in plants and fungi. Free living organism’s serves as a host for one or more number of parasites. They are evolved as a retort to host defense mechanism. For instance, plants produce toxins to protect them from parasitic bacteria and fungi is host defense mechanism of plants. When parasites attack the host, then also host defense mechanism is effective. Parasites reproduce at a greater speed than host; hence parasites are benefited out of this relationship.

Co evolutions of parasites take place as a result of strong relationship between organisms resulting in commensalisms or mutualism relationship. Host has to adopt most of the times, as parasite presence is unavoidable. When the parasites harm the host, the host is infected by its action, whereas still puncturing of host results in autoimmune disorders in the host, including human beings. As parasites and host has shared relationship, it helps in easy prediction of taxa to which they belong. Co evolution increases the interest of evolutionary concept. During the development of secondary sexual characteristics, parasitism is in picture throughout the animal taxa. Female host select males of their choice especially for breeding because many females hosts are dead set against parasites and many other influenced diseases.

Parasitic Instances

A fungus such as rhizophydium sphaerocarpum with spirogyra is parasitic relationship. Similarly rhizoctonia solani forms a parasitic relationship with algae mucor and phythium, here one organism controls the biological process of another organism.

Parasitism Role in Ecosystem Development

A parasite stands top in food web formation. It stabilizes the ecological interaction of parasitic organism with the host species as most of the parasites require one or more host. It acts as keystone species in particular when superior organism’s starts dominating the growth of other organisms, parasites play their role by co existing nature.