Popular interaction: It can be said that Population Interaction is one of the important operations that regulates the organisation of a community and refers to the interrelationship between the participants in the aggregate in a community. Organisms do not live as isolated individuals. Animals prefer to live in groups or colonies.

Two or more populations of different species interact to form a biological community. In a biological organisation, both plants and animals are very closely related. Abiotic (physical) and biotic (biological) components make up the environment. Let’s browse through the article for a detailed study of different types of population interaction and examples.

What is Population Interaction?

Definition: A population is defined as a group of individuals of the same species. The interrelationship between the individuals in an ecosystem is termed population interaction. The organisms in an interaction are most likely to be influenced by each other either positively, negatively, or neutral. Check out the population interaction PDF.

Types of Population Interaction

The interactions have been observed between the individuals of a population or between the two or more populations of different species. Also, these interactions can be either beneficial, harmful, or neutral to both or any of the interacting species. Based on these parameters, different types of population interactions can be mapped as follows:

Species A	Species B	Type of Interactions
+	0	Commensalism
+	+	Mutualism
+	+	Protocooperation
+	–	Predation
+	–	Parasitism
–	–	Competition
–	0	Ammensalism

The interaction between two individuals of different species or between two populations of different species is called interspecific interaction. These interactions could be beneficial, detrimental, or neutral. These can be described as follows:

1. Commensalism: It is an association between two different species in which one is always benefited, but another is neither benefited nor harmed. The relationship may be permanent or temporary, and the benefits derived from one organism may be protection, transportation, living space, food, etc.

i. The pilot fish (Remora) always accompanies the shark without getting attached to the same. It feeds on the falling pieces of the food when the shark eats its prey.

ii. Suckerfish reach the food resources and escape from the prey by getting attached to the shark body with the help of its dorsal fin modified into holdfast.

iii. Escherichia coli is a commensal which feeds on undigested food in the human intestine. It checks the growth of putrefying bacteria.

iv. An orchid growing as an epiphyte on a mango tree gets shelter and nutrition from the mango tree, while the mango tree is neither benefited nor harmed.

Fig: Commensalism

2. Mutualism: It is an interrelationship between two different species where both partners are benefited. It is of two types:

I. Obligate Mutualism: It is a type of association in which the interacting species are entirely dependent upon each other, and neither species can survive without the other. It is also called symbiotic association. The two organisms enter into some sort of physiological relationship.

i. Lichens represent an obligate mutualistic relationship between a fungus and photosynthetic algae or cyanobacteria. Fungi decompose the organic matter into its organic constituents and make it available for the algae for the process of photosynthesis and, in exchange, obtain the food synthesised by algae.

ii. Mycorrhizae show a close mutual association between fungi and the roots of higher plants and exchange benefits. The fungal components colonise the root tissues of the plant and provide access to phosphorus and other nutrients and also increase the surface area for water and mineral absorption, and in turn, obtain sugars (carbohydrates) from the plant.

iii. Rhizobium lives in the root nodules of leguminous plants and fixes the atmospheric nitrogen for the use of plants.

iv. Fig and wasps mutually interact. Female wasps use the fruits not only as an oviposition site but also uses the seeds of the fruits for nourishing their larvae. In return, wasps pollinate the fig inflorescence while searching for suitable egg-laying sites. Based on this example, it can be said that Plant-animal interactions often involve co-evolution of the mutualists where two or more species affect the evolution of each other through natural selection.
On the contrary, obligate mutualists show coextinction. It is the phenomenon in which the extinction of any of the two interrelated species may cause the risk of extinction of another species.

Fig: Obligate Mutualism

II. Facultative Mutualism (Protocooperation): It is an interaction between two different species in which both are often benefited but not strictly dependent on each other and hence can also survive when not involved in the mutual association.

An association of hermit crabs and sea anemones exhibits protocooperation. The sea anemone remains attached to the back of the hermit crab and carried by the crab to the fresh feeding sites. The crab, in turn, is protected from its enemy by a sea anemone.

Fig: Facultative mutualism (protocooperation)

3. Predation: It is a type of interaction between members of two different species in which one member is being killed by another. The one who kills is called the predator benefits, and the one who is being killed is called the prey who is harmed.

It is nature’s way of transferring energy to higher trophic levels which are fixed by the plants at the first trophic level. A lion eating a deer is an example of predation. 

Overexploitation of prey species might lead to their extinction. Therefore, the prey species have evolved various defences to lessen the impact of predators.

Fig: Predation

I. Camouflage is a phenomenon of disguising predators by blending themselves with their surroundings.

II. Some insects are phytophagous that feed upon plant sap and other parts of plants. Therefore plants have evolved an astonishing variety of morphological and chemical defences against their predators. For instance, thorns are the most common morphological defence in the cactus, Acacia. Calotropis produces highly poisonous glycosides; therefore, cattle do not browse this plant.

4. Parasitism: It is an association between two living organisms of different species in which one organism called a parasite obtains its food directly from the other living organism called the host. Parasites can be categorised as:

i. Ectoparasite & Endoparasite.
ii. Temporary & permanent.
iii. Holo parasite & Hemi parasite
iv. Phyto parasites
v. Pathogenic and non-pathogenic parasites
vi. Hyperparasites

Fig: Ectoparasite and Endoparasite

Adaptations for parasite life: The general parasite adaptations are as follows:

i. Parasites can respire anaerobically.
ii. They have adhesive organs to attach to the host body.
iii. Excessive multiplication is the key adaptation to maintain its existence.
iv. Loss of unnecessary sense organs.
v. Complex life cycle involving one or two intermediate hosts to facilitate parasitisation of its primary hosts. For example, the human liver fluke depends on two intermediate hosts (a snail and a fish) to complete its life
cycle. The malarial parasite Plasmodium needs a vector (mosquito) to spread to other hosts.

5. Competition: The competition may be interspecific or intraspecific. However, intraspecific competition is more acute than interspecific competition because all the species have similar requirements for food, shelter, mate, light, etc. Competition can exist in the following forms:

I. Competitive Exclusion (Gause Principle): It states that two closely related species competing for the same resources cannot coexist indefinitely. Therefore, the competitively inferior one will be eliminated. This may hold true in the case of limited resources but not in other conditions. 

i. Paramecium caudatum and Paramecium aurelia, when placed in the same culture, P. aurelia alone survived because it had a more rapid growth rate.

ii. Connell’s elegant field experiment showed that on the rocky sea coasts of Scotland, the larger and competitively superior barnacle dominates the intertidal area and excludes the small barnacle from that zone.

II. Competitive coexistence (Resource Partitioning): It states that if two species compete for the same source, they could avoid competition by choosing different times of feeding or different foraging patterns. 

i. Mac Arthur shows that five species of warblers living on the same tree avoid competition in between due to behavioural differences in their foraging activities. 

ii. Darwin finches in the Galapagos islands also exhibit coexistence.

III. Evidence of competition occurring in nature where one species is restricted to a small geographical area due to the presence of competitively superior species that expand their distributional range dramatically is called competitive release.

Summary

In nature, living organisms such as animals, plants, and microbes cannot live in isolation and therefore interact in different ways to form a biological community. These interactions may be intraspecific which occur within the same species and interspecific between two different species. Intraspecific interactions include mating, territoriality, parental care, altruism, and communication. Interspecific interaction either may be beneficial, harmful, or neutral. Mutualism, commensalism, predation, parasitism, competition, and commensalism are the types of interspecific interactions.

FAQs on Population Interaction

Students can check out some of the prominent and frequently asked questions on Population Interaction:

Q1: What are the two kinds of interactions?
Ans: The two kinds of interactions include interspecific interactions and intraspecific interactions.

Q2: What is positive population interaction?
Ans: When both the interactive species and population are benefitted, it is called positive population interaction.

Q3: What is an example of mutualism?
Ans: A relationship between Rhizobium and leguminous plants is an example of mutualism. The bacteria fix the atmospheric nitrogen for plants and obtain nutrition and shelter from the plant.

Q4: What is an example of a commensalism relationship?
Ans: The association between the suckerfish and the shark is an example of commensalism. The suckerfish reaches the food resources by attaching to the shark’s body.

Q5: What is predation behaviour?
Ans: Predation is a behaviour in which one organism is being killed by other organisms for obtaining food. The one who kills is called the predator, and the one who is being killed is called the prey.

We hope you find this article on ‘Population Interaction‘ helpful.