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Difficulty: MediumEcological Functions, Nutrient Cycles and Ecological Succession

Regarding ecological functions, nutrient cycling, and ecological succession, which of the following statements are correct?

  1. In sedimentary nutrient cycles, such as the phosphorus cycle, the principal reservoir pool is located in the Earth's crust rather than the atmosphere.Answer
  2. B
    Primary succession occurs on substrates that previously supported active biological communities but were degraded by natural disasters like wild fires.
  3. The pyramid of energy is always upright in all ecosystems because energy transfer between trophic levels is unidirectional and decreases at each step according to Lindeman's 10% law.Answer
  4. D
    Autogenic succession is driven primarily by external physical forces such as severe volcanic activity, land subsidence, or climate shifts.

Answer

The correct statements are that sedimentary nutrient cycles have their main reservoir pool in the Earth's crust and that the pyramid of energy is always upright across all ecosystems.
The statements identifying the Earth's crust as the primary reservoir for sedimentary cycles and stating that energy pyramids are strictly upright due to thermodynamic laws are both scientifically correct.

Step-by-Step Solution

1
Evaluate the statement concerning biogeochemical reservoir pools.
Phosphorus and sulfur cycles are sedimentary cycles with main reservoirs in rocks and soil sediments of the Earth's crust.
Gaseous cycles have atmospheric/aquatic reservoirs (e.g., carbon, nitrogen), whereas sedimentary cycles rely on geological weathering.
2
Evaluate the statement regarding primary succession conditions.
Primary succession takes place on newly exposed, previously uncolonized bare substrates (like volcanic lava flows or exposed rock).
Substrates affected by forest fires already contain organic soil and propagules, characteristic of secondary succession.
3
Evaluate energy dynamics and pyramid geometry.
The energy pyramid can never be inverted because energy is lost as heat at each trophic transition according to the second law of thermodynamics and the 10% rule.
Net primary productivity sets the maximum available energy base, which declines monotonically at successive consumer levels.
4
Evaluate the distinction between autogenic and allogenic succession.
Autogenic succession is brought about by the living vegetation itself changing soil organic matter, light availability, and moisture.
External geological or meteorological events induce allogenic succession.

Key Concept

Classification of Biogeochemical Cycles, Energy Flow Dynamics, and Types of Ecological Succession
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Topics

Ecological Functions, Nutrient Cycles and Ecological Succession