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Difficulty: MediumEcological Succession

During an ecological survey of a newly formed coastal sand dune (psammosere), researchers monitor changes in plant community structure, soil organic content, and microclimatic conditions over a period of 150 years. Which of the following trends accurately describes the ecological changes that occur as this primary succession progresses toward a climax community?

  1. A
    Species diversity rapidly peaks during the initial pioneer stage due to pre-existing soil seed banks, then steadily declines as climax trees establish.
  2. Both species diversity and soil organic content gradually increase, creating more stable soil and complex food webs.Answer
  3. C
    Soil organic matter steadily decreases as pioneer vascular plants absorb all available mineral salts without returning biomass to the soil.
  4. D
    Total biomass decreases while net primary productivity reaches its maximum value only at the final climax stage.

Answer

Both species diversity and soil organic content gradually increase, creating more stable soil and complex food webs.
In primary succession on a sand dune, pioneer plants colonize bare substrate and gradually decompose, accumulating soil organic matter (humus). This soil improvement enhances water and nutrient retention, enabling succession through intermediate seral stages toward a climax community characterized by high species diversity and ecosystem stability.

Step-by-Step Solution

1
Identify the type of ecological succession described in the scenario.
The formation of a coastal sand dune represents primary succession because it starts on a newly exposed, bare substrate with no initial soil or organic material.
Differentiating primary from secondary succession establishes the baseline substrate conditions (absence vs. presence of pre-existing soil).
2
Analyze ecosystem property trends (biomass, species diversity, soil structure) across seral stages.
Pioneer species bind the loose sand and decompose upon dying, generating initial soil humus. Subsequent seral stages build deeper soil, higher water retention, and greater niche diversity.
Understanding ecological succession dynamics requires tracing how early colonizers modify abiotic conditions to facilitate colonization by later species.
3
Evaluate the options against standard succession principles.
The statement indicating that both species diversity and soil organic content gradually increase toward the climax community is scientifically accurate.
Climax communities characteristically display maximal species diversity, high total biomass, and well-developed soil layers compared to early pioneer stages.

Key Concept

Trends in Ecosystem Properties During Primary Succession
Estimated Time:1m 15s
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Topics

Ecological Succession

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