Biotic Interactions

Biotic interactions occur when organisms living in the same community directly or indirectly influence one another, either in positive, negative or in neutral manner. Understanding these interactions such as amensalism, predation etc.  guides conservation efforts and sustainable resource management. In this article, you will learn about what is Biotic Interactions, and its various types. It is important topic for GS Paper-3 Environment & Ecology of UPSC IAS Exam. To explore other interesting Environment & Ecology concepts similar to Biotic Interactions, check out other articles of IASToppers.    

Table of Content

• What is Biotic Interaction?
• Types of Biotic Interactions
• Conclusion  
• FAQs on Biotic Interactions

What is Biotic Interactions?

• Biotic interaction refers to the interaction taking place between individuals belonging to the same species (intra specific) or different species (interspecific).

Types of Biotic Interactions

Possible biological interactions between two species

Type of interaction		Effects of interaction
Negative Interactions	Amensalism	One species is inhibited while the other species is unaffected
	Predation	Predator–prey relationship: one species (predator) benefits while the second species (prey) is harmed and inhibited.
	Parasitism	Beneficial to one species (parasite) and harmful to the other species (host).
	Competition	Adversely affects both species
Positive Interactions	Commensalism	One species (the commensal) benefits, while the other species (the host) is neither harmed nor inhibited
	Mutualism	Interaction is favourable to both species
Neutral Associations	Neutralism	Neither species affects the other

Amensalism:

• This is a negative association between two species.
• One organism negatively impacts or hinders the other without being negatively affected itself.
• Some organisms release antibiotics, inhibiting the growth of other species.

Example

• Fungus Penicillium produces penicillin, an antibiotic that suppresses various bacteria. Penicillium gains an advantage by having more food resources when competing bacteria are eliminated.

Predation:

• Predation occurs when one organism, the predator, captures, kills, and consumes another organism, known as the prey.
• The predator benefits from this interaction, while the prey is harmed.

Example:

• Predators like leopards, tigers and cheetahs use speed, teeth and claws to hunt and kill their prey.

Parasitism:

• The parasitic relationship involves a smaller organism, the parasite, living in or on another organism, the host, from which it derives nourishment and sometimes shelter.
• The host is harmed, while the parasite benefits.
• Various organisms, including animals, bacteria, and viruses, are parasites of plants and animals.

Example:

• Plants like dodder plant (Cuscuta) and mistletoe (Loranthus) are parasites that live on flowering plants.
• Tap worm, round worm, malarial parasite, many bacteria, fungi, and viruses are common parasites of humans.

Competition:

• Competition involves an interaction between two populations where both species are negatively affected to some degree.
• Competition occurs when two species need a vital resource such as food, water, shelter, nesting site etc. that is in short supply.

Various ways through which species compete are shown below:

By mechanism:

• Biologists have identified two primary forms of competition: 1) Direct competition, also known as interference competition, and 2) Indirect competition, or exploitative competition.
• During interference competition, organisms come into contact with one another as they vie for limited resources.
  • Example: Large aphids defend feeding sites on cottonwood leaves by ejecting smaller aphids from better sites.
• In indirect competition, organisms compete without direct interaction by using up limited resources.
  • Example: Plants consume nitrogen by absorbing it into their roots, making nitrogen unavailable to nearby plants.

By size asymmetry

• Competition can range from entirely symmetric (all individuals obtain an equal share of resources, regardless of their size) to perfectly size-symmetric (all individuals utilize the same quantity of resources per unit biomass) to completely size-asymmetric (the largest individuals use up all available resources).
• The extent of size asymmetry greatly influences the structure and diversity of ecological communities.
• Example: In plant communities’ size-asymmetric competition for light has stronger effects on diversity compared with competition for soil resources

By taxonomic relationship

• Competition may arise among members of the same species, referred to as intraspecific competition, or among different species, known as interspecific competition.
• Intraspecific competition can regulate population dynamics (changes in population size over time). This occurs because individuals become crowded as population grows.
• Due to the fact that members of a population all need the same resources, the increase in crowding leads to a scarcity of resources.
• Eventually, some individuals fail to obtain sufficient resources and either die or do not reproduce. This causes a decrease in population size and a slowing of population growth.

Example:

• Cheetahs and lions both rely on similar prey, meaning that their food supply is negatively affected by the presence of the other species. However, they continue to coexist, even though the expectation under competition would be for one to drive the other away.

Commensalism:

• In this relationship, one of the species benefits while the other is neither harmed nor benefited.
• Some species obtain the benefit of shelter or transport from another species.

There are two types of commensalisms:

Ecto-commensalism:  Here, the commensal lives on the body of the other partner, which may be called host.

Example:

• Remoras, or suckerfish, attach to sharks using a suction disc on their heads. This allows the remoras to gain protection and feed on the shark’s leftovers. The shark is neither helped nor harmed by this relationship.
• Epiphytes, including ferns, mosses, and orchids, grow on the surfaces of other plants to gain support and access to sunlight and moisture. The host tree does not benefit from or get harmed by this interaction.

Endo-commensalism: Here the commensal lives within the body of host.

Example:

• Tropical marine fish Fierasfer lives inside the cloacal chamber of sea cucumbers where the fish gets protection from enemies.
• A variety of microorganisms, saprophytic bacteria and fungi and protozoans live within the tissues or cavities of higher plants and animals.
• E. coli lives in the intestine of humans.

Mutualism:

• In this, there is a close association between two species in which both the species benefit.

Example

• Sea anemone gets attached to the shell of hermit crabs for benefit of transport and obtaining new food while the anemone provides camouflage and protection by means of its stinging cells to the hermit crab.
• However, some mutualisms are so intimate that the interacting species can no longer live without each other as they depend totally on each other to survive. Such close associations are called symbiosis.

Example of symbiosis:

1. Termites can consume wood but lack the enzymes to digest it. They have protozoans in their intestines that can break down the wood into sugar. Both the termite and the protozoans benefit from this relationship.

Protocooperation

• Itis a form of mutualism, but the cooperating species do not depend on each other for survival.

Example: 

• The flowers of plants that are pollinated by insects benefit from protocooperation. The plants, particularly those with large bright colourful flowers, experience cross pollination because of the insects activities. This is beneficial to the insect that has got the food sue pollen and nectar required for its survival.
• Certain fish perform the task of cleaning other fish, by removing parasites, cleaning wounded flesh and getting rid of dead flesh.

Neutralism:

• Neutralism describes the relationship between two species which do interact but do not affect each other.
• The term is used when one species’ fitness has no impact on the other species.
• Since true neutralism is rare or non-existent, its usage is often extended to situations where interaction is merely insignificant or negligible.

Conclusion

Biotic interactions in an ecosystem encompass a diverse range of relationships among organisms that can be negative, positive, or neutral. These interactions are critical to understanding ecosystem dynamics and biodiversity, ultimately guiding conservation and sustainable resource management efforts.

Ref:

Source-1

FAQs(frequently asked question)