Examkin

Question

Difficulty: HardEcological Succession

An ecologist compared two disturbed ecosystems: Site X, an abandoned agricultural field where topsoil and organic seed banks remained intact, and Site Y, a newly exposed volcanic basalt ledge devoid of organic soil. Which of the following observations correctly contrasts the ecological succession dynamics between Site X and Site Y?

  1. Site X undergoes secondary succession characterized by rapid colonization from surviving seeds and soil microbes, whereas Site Y undergoes primary succession requiring crustose lichens to initiate substrate weathering.Answer
  2. B
    Site X undergoes primary succession starting with pioneer lichen species that lack true vascular tissues, while Site Y undergoes secondary succession driven by deep-rooted woody shrubs.
  3. C
    Site Y undergoes primary succession initiated by pioneer mosses that utilize specialized xylem and phloem to extract nutrients directly from unweathered rock.
  4. D
    Both sites undergo secondary succession at identical rates because initial soil presence does not influence pioneer community establishment or species turnover.

Answer

Site X undergoes secondary succession characterized by rapid colonization from surviving seeds and soil microbes, whereas Site Y undergoes primary succession requiring crustose lichens to initiate substrate weathering.
The correct answer accurately identifies that Site X undergoes secondary succession because topsoil and organic propagules are already present, allowing for rapid vegetation recovery. Conversely, Site Y undergoes primary succession on bare volcanic rock, where pioneer species like crustose lichens must first colonize, secrete organic acids to weather substrate, and accumulate organic matter before vascular plants can establish.

Step-by-Step Solution

1
Analyze the starting substrate conditions of Site X and Site Y.
Site X has pre-existing topsoil, organic matter, and seed banks (abandoned agricultural field). Site Y has bare volcanic basalt with no pre-existing soil.
The presence or absence of pre-existing soil determines whether succession is primary or secondary.
2
Determine the type of ecological succession and pioneer organisms for each site.
Site X undergoes secondary succession (rapid, starts with grasses/herbaceous plants). Site Y undergoes primary succession (slow, starts with lichens/mosses to form soil).
Secondary succession builds upon established soil, whereas primary succession must build soil from uncolonized substrate.
3
Evaluate the option statements against established ecological principles.
The statement identifying Site X as secondary succession and Site Y as primary succession initiated by lichen weathering is correct.
Lichens secrete organic acids that weather bare rock into soil, enabling subsequent plant establishment during primary succession.

Key Concept

Distinction between primary and secondary ecological succession based on initial soil availability and pioneer community traits
Rate this question

Topics

Ecological Succession

More questions from this topic