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Question

Difficulty: EasyEcological Succession

An abandoned agricultural field is left uncultivated for several years. Within a few months, wild grasses and annual weeds rapidly cover the area, leading eventually to a shrubland community. Which of the following factors primarily explains why plant establishment occurs so quickly during this secondary succession process?

  1. The presence of pre-existing soil containing nutrients, micro-organisms, and a seed bankAnswer
  2. B
    The initial weathering of bare basaltic rock by pioneer lichen species
  3. C
    The dependence on non-vascular bryophytes to synthesize vascular tissues for invading shrubs
  4. D
    The complete removal of all organic matter and soil nutrients prior to plant colonization

Answer

The presence of pre-existing soil containing nutrients, micro-organisms, and a seed bank primarily accounts for rapid colonization in secondary succession.
Secondary succession occurs following a disturbance in an area where an ecosystem previously existed, leaving the soil intact. This pre-existing soil layer contains essential plant nutrients, organic matter, and dormant seeds, allowing fast-growing weeds and grasses to establish rapidly without the prolonged phase of soil creation required in primary succession.

Step-by-Step Solution

1
Identify the type of ecological succession described in the scenario.
Since the disturbance occurred on an abandoned agricultural field where soil already existed, this is secondary succession.
Secondary succession begins in environments where an established biological community was disturbed, but the soil substrate remains intact.
2
Determine the primary ecological advantage of secondary succession over primary succession.
Pre-existing soil contains organic matter, moisture, beneficial soil microbes, and buried seeds (seed bank), enabling fast colonization without waiting for soil formation.
Primary succession requires pioneer species like lichens to break down bare rock into soil, which is a very slow process.

Key Concept

Secondary Ecological Succession
Estimated Time:45s
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Topics

Ecological Succession

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