Community Ecology

AP Biology· difficulty 3/5

Two Paramecium species were grown alone and together in standardized cultures. The graph shows population density over 16 days.

Day Population P. aurelia alone P. caudatum alone aurelia (mix) caudatum (mix)

What does the comparison of mixed and single cultures demonstrate?

  • A

    P. aurelia thrives only in the presence of P. caudatum.

  • B

    P. caudatum cannot survive alone.

  • C

    Competitive exclusion: P. aurelia outcompetes P. caudatum when resources overlap.

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  • D

    Both species coexist stably.

Explanation

Both grow well alone, but in coculture P. caudatum is driven toward extinction while P. aurelia thrives, illustrating Gause's principle of competitive exclusion.

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