Chapter 4 Principles of Ecology

NIOS Class 12 Environmental Science Chapter 4

INTEXT QUESTIONS 4.1

1. What does the term ecology mean?

Ans: ‘Ecology may be defined as the scientific study of the relationship of living organisms with each other and with their environment.’

2. Define the term niche.

Ans: The term niche means the sum of all activities and relationships a species has while obtaining and using the resources it needs to survive and reproduce.

3. Give one point of difference between habitat and niche.

Ans: Habitat is the physical environment where an organism lives, while niche is the sum of all activities and relationships of a species

INTEXT QUESTIONS 4.2

1. What is meant by the term adaptation? Answer in one sentence.

Ans: The appearance or behaviour or structure, or mode of life of an organism that allows it to survive in a particular environment.

2. Define : (i) species (ii) variation

Ans:

Species – a group of similar populations of organisms whose members are capable of interbreeding to produce fertile offspring.
Variation- differences in structure due to differences in gene combinations.

3. Name two sources of variation.

Ans: (i) Gene combination (ii) Mutation

4. Name the evolutionary force which brings about greater reproduction of adaptive variation.

Ans: Natural selection

5. Explain the terms (i) speciation and (ii) extinction.

Ans: Speciation is the process by which new species are formed, and evolution is the mechanism

by which speciation is brought about. Extinction is the dying out of a variety or a species.

INTEXT QUESTIONS 4.3

1. Define population.

Ans: Population is a group of freely interbreeding individuals of the same species present in a specific area at a given time.

2. Name at least three characteristics of a population.

Ans:

i) Density of the population

ii) Natality

iii) Mortality (any other)

3. What are the factors on which the density of a population depends?

Ans: Mortality, natality, immigration, emigration

INTEXT QUESTIONS 4.4

1. Explain in brief (one to two sentences) the following ecological terms:

(i) Succession.

(ii) Pioneer species.

(iii) Climax community

(iv) Secondary succession

Ans:

(i) Succession is the orderly change of organisms in an environment over time.
(ii) Pioneer species is the name used for the first time assemblage of plants that inhabit an area that is changing succession. They are the first species in the successional process.
(iii) Climax community is the final stage of succession. It is a relatively stable, long-lasting community.
(iv) Secondary succession is the term used for the orderly series of changes that begins with the disturbance of an existing community and leads to a climax community

INTEXT QUESTIONS 4.5

1. Define (a) ecological succession, (b) symbiosis

Ans: The interacting species can no longer live without each other as they depend totally on each other to survive.

2. What type of competition exists between members of a deer herd in an area?

Ans: Intraspecific competition

3. What type of relationship is represented by a garden spider feeding on a grasshopper?

Ans: Predation. It is preying upon or eating the grasshopper.

4. What type of relationship is represented by a flower being pollinated by a butterfly?

Ans: Mutualism as both are helped by the relationship.

5. Which term best fits the relationship of a person who has lice feeding on his scalp?

Ans: Host

6. Which term means two species live together, with each providing a benefit to the other through the relationship?

Ans: Mutualism

TERMINAL EXERCISE

1. Define the terms: Ecology, niche, species, and extinction.

Ans:

Ecology: ‘Ecology may be defined as the scientific study of the relationship of living organisms with each other and with their environment.’
Niche: The term niche means the sum of all activities and relationships a species has while obtaining and using the resources it needs to survive and reproduce.
Species: A Species is a group of similar populations of organisms whose members are capable of interbreeding to produce fertile offspring.
Extinction: Extinction is the dying out of a variety or a species.

2. What do you understand by ‘Variation and Natural Selection’? In what way do they interact to cause evolution?

Ans: Variation is the difference in structure due to differences in gene combinations. Variations are produced as a result of chance mutation. Competition and natural selection determine which variation will succeed and survive. Those variations that enable a species to survive in the struggle for existence are encouraged and promoted. These variations are heritable. Natural selection selects among variations, i.e. genes that help the organism to adapt to its environment. Such genes are reproduced more in a population due to natural selection. This leads to the evolution of species that are able to survive better.

3. What is the role of isolation in the formation of new species and keeping them distinct?

Ans: Often, different populations of a species remain isolated due to some geographic barrier such as a mountain, ocean, river, etc. Geographic isolation occurs when a physical barrier develops between two populations of a species.

The isolating mechanism may be a physical barrier like water, a mountain, ocean represents geographical isolation. The most common way a population undergoes speciation is by geographic isolation.

The members of a population of a species live in a particular environment and are capable of breeding with members of another population of the same species.
The population then becomes separated into two completely isolated populations by a barrier which prevents their interbreeding and gene exchange.

4. In what ways have humans caused the extinction of species?

Ans: Human activities such as deporation, over-exploitation, environmental pollution and environmental change are other factors responsible for extinction. Deforestation for the expansion of industries and human settlements has promoted economic growth, but at the same time, it has resulted in habitat loss for many wild plants and animals. Pollution has killed many aquatic species.

5. What do you understand by (i) natality, (ii) speciation, (iii) mutation, (iv) extinction

Ans:

Natality: The rate at which new individuals are born and added to a population under given environmental conditions is called natality.
Speciation: Speciation is the process by which new species are formed, and evolution is the mechanism by which speciation is brought about.
Mutation: Mutation is the change in genetic material that results from an error in replication of DNA, which causes new genes to arise in a population.
Extinction: Extinction is the dying out of a variety or a species.

6. Explain ‘ecological succession’.

Ans: The process by which communities of plant and animal species in an area are replaced or changed into another over a period of time is known as ecological succession. Both the biotic and abiotic components are involved in this process. This change is brought about by the activities of communities and the physical environment in that particular area. The physical environment often influences the nature, direction, rate and optimal limit of changes.

7. State and explain community characteristics.

Ans: An important attribute of a community is its species diversity. The different kinds of organisms present in a community represent its species diversity. The species composition or diversity differs from one community to another. Even in the same community, there may be seasonal variation in species composition.

Species diversity also influences the stability of the community. A stable community can return to its original condition after being disturbed in some way. Communities with high species diversity are comparatively more stable.

8. What are (i) climax community and (ii) pioneer species?

Ans:

The terminal (final) stage of succession forms the community, which is called as climax community. A climax community is stable, mature, more complex and long-lasting.
The community that initially inhabits a bare area is called a pioneer community. The pioneer community, after some time, gets replaced by another community with a different species combination.

9. Write an essay on biotic interaction.

Ans: The biological community of an area or ecosystem is a complex network of interactions. The interaction that occurs among different individuals of the same species is called intraspecific interaction, while the interaction among individuals of different species in a community is termed interspecific interaction.

Individuals of the population may compete for food, space and mates. This competition may be intraspecific as well as interspecific. Interspecific relationships may be direct and close, as between a lion and a deer or indirect and remote, as between an elephant and a beetle.

Types of Interactions

Amensalism: One species is inhibited while the other species is unaffected
Predation: 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
Commensalism: One species (the commensal) benefits, while the other species (the host) is neither harmed nor inhibited.
Mutualism: Interaction is favourable to both species
Neutralism: Neither species affects the other

10. Define biotic Interaction. Describe any one type of positive, negative and neutral quotation.

Ans: Biotic interaction refers to the interaction taking place between individuals belonging to the same species (intraspecific) or different species (interspecific).

Positive: Commensalism, where one species benefits while the other species is neither harmed nor inhibited. Eg. For example sucker fish, remora, often attaches to a shark.
Negative: Predation is where one species benefits while the other one is harmed and inhibited. Predators like leopards, tigers and cheetahs use speed, teeth and claws to hunt and kill their prey.
Neutral: Neutralism is where neither species affects the other.