UPSC CIVIL SERVICES EXAMINATION

PRELIMS 2019 SPECIAL

LECTURE 29

MCQs – STATIC – ENVIRONMENT

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FUNCTIONS OF ECOSYSTEM

FUNCTIONS OF

ECOSYSTEM

ENERGY FLOW

ECOLOGICAL SUCCESSION

NUTRIENT CYCLING

HOMEOSTASIS

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FUNCTIONS OF ECOSYSTEM

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What is Ecological Succession?

Important Terminologies Pioneer Community Climax Community

Types of Ecological SuccessionPrimary Succession

Secondary Succession

Autogenic Succession

Allogenic Succession

Autotrophic Succession

Heterotrophic Succession

ECOLOGICAL SUCCESSION

Succession is a progressive series of changes which leads to the establishment of a relatively stable climaxcommunity.

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Succession is a universal process of directional change in flora and fauna on an ecological time scale. It occurswhen a series of communities replace one another due to large scale destruction either natural or manmade.

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EXAMPLE OF ECOLOGICAL SUCCESSION

HYDROSERE is the primary succession sequence which develops in aquatic environments such as lakes and ponds.

It represents a conversion of water body and its community into a land community. For example an oxbow lake or a kettle lake – over time, an area of open freshwater will naturally dry out.

Ultimately, it will become woodland, after going through several different stages.

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A very common example is succession of open freshwater habitats into woodlands.

CLIMAX COMMUNITY –FOREST OR WOODLAND

PIONEER COMMUITY –ALGAE – unicellular floating plants

ECOLOGICAL SUCCESSION

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The first plant to colonize an area is called the pioneer community.For example, in ecological succession hydrosere, the pioneer community is the Algae (unicellular floating plants).

ECOLOGICAL SUCCESSION

PIONEER COMMUNITY

The final stage of succession is called the climax community.For example, in ecological succession – hydrosere – the climax community would be a forest if the climate ishumid, grassland in case of sub-humid environment, or a desert in arid and semi-arid conditions.A forest is characterized by presence of all types of vegetation including herbs, shrubs, mosses, shade-lovingplants and trees.

CLIMAX COMMUNITY

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TYPES OF SUCCESSIONS

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PRIMARY SUCCESSION SECONDARY SUCCESSION

AUTOGENIC Succession ALLOGENIC Succession

AUTOTROPHIC Succession HETEROTROPHIC Succession

PRIMARY SUCCESSION

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Pioneer Colonisation

• In primary succession on a terrestrial site the new site is first colonized by a few hardy pioneer species that are often microbes, lichens and mosses.

• The pioneers over a few generations alter the habitat conditions by their growth and development.

New Conditions

• The new conditions may be conducive to the establishment of additional organisms that may subsequently arrive at the site.

• The pioneers through their death any decay leave patches of organic matter in which small animals can live.

Addition of Nutrients

• The organic matter produced by these pioneer species produce organic acids during decomposition that dissolve and etch the substratum releasing nutrients to the substratum.

• Organic debris accumulates in pockets and crevices, providing soil in which seeds can become lodged and grow.

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Increase In Diversity

• As the community of organisms continues to develop, it becomes more diverse and competition increases, but at the same time new niche opportunities develops.

Replacement Of Communities

• The pioneer species disappear as the habitat conditions change and invasion of new species progresses, leading to the replacement of the preceding community.

Climax Community

• Ultimately, a series of succession of leads to finally leads to the establishment of a more stable climax community.

PRIMARY SUCCESSION

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Destruction of Mature

Community

• A mature or intermediate community may be destroyed by natural events such as floods, droughts, fires, or storms or by human interventions such as deforestation, agriculture, overgrazing, etc.

New Conditions

• This abandoned farmland is first invaded by hardy species of grasses that can survive in bare, sunbaked soil.

• These grasses may be soon joined by tall grasses and herbaceous plants. These dominate the ecosystem for some years along with mice, rabbits, insects and seed-eating birds.

SECONDARY SUCCESSION

Secondary succession occurs when plants recognize an area in which the climax community has been disturbed.It is the sequential development of biotic communities after the complete or partial destruction of the existingcommunity.

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Climax Community

• Eventually, some trees come up in this area, seeds of which may be brought by wind or animals.

• And over the years, a forest community develops.

• Thus an abandoned farmland over a period becomes dominated by trees and is transformed into a forest – CLIMAX COMMUNITY

SECONDARY SUCCESSION

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ECOLOGICAL SUCCESSION

When the succession is brought about by living inhabitants of that community itself, the process is called iscalled as autogenic succession.It can be viewed as a secondary succession because of the pre-existing plant life.

AUTOGENIC SUCCESSION

When the succession is an outcome of the changes brought about by the outside forces is known as allogenicsuccession.

ALLOGENIC SUCCESSION

Succession in which, initially the green plants are much greater quantity is known as autotrophic succession.Example -

AUTOTROPHIC SUCCESSION

Succession in which, initially the heterotrophs are much in much greater quantity is known as autotrophicsuccession.

HETEROTROPHIC SUCCESSION

Q. Ecological Succession is an important function of an Eco-system. Which of the following

statement/s about Ecological succession is/are correct?

1) Succession refers to the changes in population or community structures that occur at the

boundary of two habitats.

2) It is a universal process of directional change in vegetation and animal life on an ecological time

scale.

Select the correct code:

a) 1 only

b) 2 only

c) Both 1 and 2

d) Neither 1 nor 2

Answer : b

QUESTION 1

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Q. Ecological succession is a universal process of directional change in vegetation and animal

life on an ecological time scale. Which of the following is/are not the characteristics of

ecological succession?

1) Increased productivity

2) Shift of the nutrients from the reservoirs

3) Decrease in diversity of organisms

4) Development of relatively less complex food webs

Select the correct code:

a) 1 and 2 only

b) 3 and 4 only

c) 1, 3 and 4 only

d) None of the above

Answer : b

QUESTION 2

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Q. In context of ecological successions consider the following statements regarding primary and

secondary succession and identify the incorrect statement/s:

1. Primary Succession starts on a well-developed soil already formed at the site.

2. As compared to the secondary succession, the primary succession is relatively faster.

Select the correct code:

a) 1 only

b) 2 only

c) Both 1 and 2

d) Neither 1 nor 2

Answer : c

QUESTION 3

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Q. In context of types of ecological successions, consider the following statements and identify

the correct one/s:

1. Autogenic Succession is brought about by living inhabitants of the community itself.

2. Allogenic Succession is brought about by the external forces.

Select the correct code:

a) 1 only

b) 2 only

c) Both 1 and 2

d) Neither 1 or 2

Answer : c

QUESTION 4

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Q. Consider the following statements regarding ecological succession and follow the

instructions:

Assertion (A) – Succession would occur faster in the area surrounded by oceans.

Reason (R) – Seeds of plants belonging to different seres reach faster in areas located in the middle of a

continent.

Select the correct code:

a) Both (A) and (R) are correct and (R) is the correct explanation for (A)

b) Both (A) and (R) are correct and (R) is the correct explanation for (A)

c) (A) is true but (R) is false

d) (R) is true but (A) is false

Answer : d

QUESTION 5

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Q. In context of ecological succession from open fresh water habitat into woodland Arrange the

following communities in the correct sequence of succession (i.e. from pioneer community to

climax community)

1. Shrubs

2. Ferns

3. Moss

4. Herb

5. Oak

Select the correct code:

a) 3-2-3-1-5

b) 2-3-4-1-5

c) 3-4-2-1-5

d) 3-1-4-2-5

DO IT YOURSELF

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