Symbiosis: Definition and Types

Introduction

An ecosystem comprises of the biotic and abiotic factors. Organisms living together in an ecosystem interact with the biotic and abiotic factors of that ecosystem. These interactions can be among the population or the community. The interactions occur mainly for food and sometimes also for space, mates, territories, etc. 

Explanation:

Types of Interactions: 

Three main types of interactions have been described by ecologists through which species and individuals affect each other.  

They are as follows: 

1. Predatory and prey relationships 

2. Competitive relationships 

3. Symbiotic relationships 

We have already studied the first two, i.e., prey predatory, and competitive relationships. Predatory and prey relationships occur between a predator, who kills another organism to obtain energy, and the prey, who gets eaten in the process. This relationship is seen in a community and not in a population. 

Competitive relationships can occur between a population or a community. If competition occurs between members of the same species, i.e., a population, then it is called intraspecific competition. Whereas if the competition occurs between members of different species, i.e., between a community, then it is called interspecific competition. 

Symbiosis: 

Symbiotic relationship occurs when species have very close interactions with other species. It is a close and long-term association between two or more species. Symbiotic relationships benefit at least one interacting species. Symbiotic relationships are of three types. 

Types of Symbiosis: 

Symbiotic relationships are classified into three types based on the behavior of interacting species. They are as follows: 

1. Mutualism: Both the interacting species benefit from each other. 

2. Commensalism: only one species is benefitted, and the other is harmed. 

3. Parasitism: one species is benefitted, and the other is harmed. 

Mutualism: 

A symbiotic association that benefits both participants is called mutualism. For example, when a bee sucks the nectar from a flower, the pollen is transferred from the flower to the body of the bee. When the bee visits another flower, the pollen on the bee is then transferred to the new flower. 

Due to this interaction, the bee finds food for itself, and the flower receives the pollen required for reproduction. 

Mutualism can also be seen between some corals and the algae that live inside these corals. In this association, the coral receives the extra nourishment and food produced by the algae through photosynthesis, and the algae receive a place to live. The algae also receive some nutrients from the coral. 

As a result, both individuals benefit from this relationship. 

Different species of “cleaner fish” exhibit mutualism while providing a service to larger fish and other animals. These cleaner fish consume parasites or dead skin from the larger fish. The larger fish provides a nourishment source and protects the cleaner fish from enemies. Divers have also found cleaning stations where larger animals line up so that these smaller animals can clean them off. Both animals benefit from this relationship. 

Various mutualistic associations can be seen in different ecosystems. Some examples of mutualism include: 

1. The sea anemone and clownfish 

2. Bacteria living in the digestive tract of humans 

3. Legume root and bacteria 

4. Termites and bacteria 

Commensalism: 

A symbiotic association in which only one organism benefits and the other remains unaffected is called commensalism. One species might use the other species for transportation, shelter or some other purpose. 

For example, the remora fish attaches itself to the body of the shark or any other larger fish. The remoras “hitch-hike” a ride from the sharks and feed on remains of food left on the shark’s body.  

As a result, the remoras benefit, and the shark remains unaffected. 

Many weed species produce spiky burrs that connect to the hair on the animal’s fur. As the animal travels to different places, these burrs fall off and thereby distributes the seeds from which new weeds grow. Due to this interaction, the weed species reproduce, and the transporting animal remains unaffected. 

 Some other examples of commensalism include: 

• The cattle and the egret 

• A spider using a tree to build its web 

Parasitism: 

A symbiotic association that benefits one participant but harms the other is called parasitism. The organism that receives all the benefits is called the parasite. Whereas the organism that is harmed by this relationship is called the host. The parasite feeds on the host and gets nourishment from it while the host is harmed in this process. 

Sometimes, when the host dies, the parasite has to find a new host. Parasitism can be seen in organisms like ticks, lice or worms. Different parasites stay in different places in the host. 

For example, some parasites like ticks and mistletoes live on the host. Ticks often move from one host to the other. 

A lot of species of wasps are parasitic. The parasitic female wasps lay their eggs inside the bodies of other insects or spiders. As the young wasps develop, they feed on their host and eventually kill their host. In this time, the young wasps are able to survive on their own. They later emerge from the host and complete their life cycle. 

Sometimes pet animals have to be treated for worms. Roundworms are common in dogs. The roundworm attaches itself to the inside of the dog’s intestine and feeds on nutrients in the dog’s blood. The dog may have abdominal pain, diarrhea, and bloating. If the infection is severe, the dog might die.  

Parasites like tapeworms, roundworms, etc., live their adult lives inside the body of the host. Other examples of parasitism include:  

1. Mosquitos and fleas 

2. Head lice 

Summary

• Symbiotic relationship occurs when species have very close interactions with other species. It is a close and long-term association between two or more species.
• Symbiosis is of three types; mutualism, commensalism, and parasitism.
• A symbiotic association that benefits both participants is called mutualism.
• A symbiotic association in which only one organism benefits and the other remains unaffected is called commensalism.
• A symbiotic association that benefits one participant but harms the other is called parasitism.
• The organism that receives all the benefits is called the parasite. Whereas the organism that is harmed by this relationship is called the host.
• The parasite feeds on the host and gets nourishment from it while the host is harmed in this process.