UPSC Prelims 2013 Q23: Environment & Ecology – Ecosystems & Ecology Concepts

UPSC Prelims 2013, General Studies Paper I · Environment & Ecology

Which one of the following is the correct sequence of ecosystems in the order of decreasing productivity?

Answer: (c) Mangroves, grasslands, lakes, oceans

Explanation

Ecosystems in order of decreasing productivity

Productivity here means the organic matter made per unit area in a year.

Rank	Ecosystem	Why
1	Mangroves	Warm, wet, rich in nutrients brought by rivers and tides
2	Grasslands	Good sunlight; limited by water
3	Lakes	Limited by light and nutrients in deeper water
4	Oceans	Open ocean is a 'marine desert': very few nutrients at the surface

Most and least productive ecosystems:

Highly productive	Poorly productive
Tropical rain forests	Deserts
Estuaries, mangroves, coral reefs	Open ocean
Swamps and marshes	Tundra

The open ocean still makes a large total amount, only because it is so vast.

Answer: (c) Mangroves, grasslands, lakes, oceans.

(a) Incorrect. Oceans are the least productive per unit area, not the most.
(b) Incorrect. Oceans cannot come second; grasslands and lakes are more productive.
(c) CORRECT. Decreasing productivity: mangroves, grasslands, lakes, oceans.
(d) Incorrect. Oceans are placed first here, which is wrong.

Productivity per unit area: mangroves and estuaries highest; then grasslands; lakes; open ocean lowest ('marine desert').

Mangroves most, open ocean least.

Confusing total production (oceans are large) with production per unit area.
Assuming all aquatic systems are highly productive.
Forgetting that estuaries and mangroves rival rain forests.

Where land meets sea, productivity peaks. The open ocean is a desert.