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Difficulty: HardBasic Concepts of Ecology and Ecosystem Structure

With reference to the structural and functional attributes of ecological systems, evaluate the following assertions:

I. The standing crop of an ecosystem refers to the total amount of inorganic nutrients present in the soil or water column at any given time.
II. In deep aquatic ecosystems, the pyramid of biomass can be inverted because the turnover rate of primary producers is exceptionally high relative to primary consumers.
III. The realised niche of a species is typically broader than its fundamental niche because interspecific competition forces the species to expand its resource utilization.

Which of the assertions given above is/are correct?

  1. II onlyAnswer
  2. B
    I and II only
  3. C
    I and III only
  4. D
    II and III only

Answer

Only assertion II is correct. The standing crop refers to living organic material (biomass), whereas standing state refers to inorganic nutrients. The realised niche is narrower than the fundamental niche due to competition.
Only the assertion stating that the pyramid of biomass in deep aquatic ecosystems can be inverted due to rapid turnover rates of primary producers is correct. Phytoplankton have high productivity and fast growth cycles, enabling a small standing mass to sustain a larger biomass of consumers. The assertion regarding standing crop is incorrect because standing crop measures living biomass, whereas the inorganic nutrient content is termed standing state. The assertion regarding niche size is incorrect because competition shrinks the fundamental niche down to a smaller realised niche.

Step-by-Step Solution

1
Evaluate Assertion I regarding ecosystem structural terminology.
Assertion I is incorrect.
The total quantity of inorganic nutrients (such as nitrogen, phosphorus, and calcium) present in an ecosystem's soil or water body at any given time is defined as the 'standing state' (or standing quality). In contrast, 'standing crop' represents the living organic matter (biomass) or total number of living organisms in a given area at a specific time.
2
Evaluate Assertion II regarding ecological pyramids in aquatic systems.
Assertion II is correct.
In open ocean and lake ecosystems, primary producers (phytoplankton) reproduce rapidly and have extremely short life cycles. Because of this high turnover rate, a small standing biomass of phytoplankton can support a significantly larger standing biomass of long-lived primary consumers (zooplankton and fish), creating an inverted biomass pyramid.
3
Evaluate Assertion III regarding ecological niche dynamics.
Assertion III is incorrect.
The fundamental niche represents the full theoretical spectrum of environmental conditions and resources a species can exploit in the absence of biotic interactions. Biological constraints—primarily interspecific competition and predation—restrict the species to a narrower actual range known as the realised niche.

Key Concept

Structural terminology of ecosystems (standing crop vs. standing state), inverted pyramids of biomass, and niche theory (fundamental vs. realised niche).
Estimated Time:2m 0s
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Topics

Basic Concepts of Ecology and Ecosystem Structure