Definition of facultative in English:

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Pronunciation: /ˈfakəlˌtādiv/


1Occurring optionally in response to circumstances rather than by nature: prison-style, facultative homosexuality
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  • Snakes of both groups ate readily, showing that reproduction-associated anorexia was a facultative response to lack of prey in the den.
  • Although the sample is small, this is a powerful test of the facultative response of females to changes in the composition of their group.
  • This paucity of experimental data makes it difficult to identify the ecological conditions that favor the evolution of the facultative response and of the particular environmental cues that may trigger it.
1.1 Biology Capable of but not restricted to a particular function or mode of life: a facultative parasite Often contrasted with obligate.
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  • Many species of Chlamydomonas are facultative auxotrophs, capable of utilizing acetate as their sole carbon and energy source.
  • Hughes argued that egg mimicry provides additional evidence that Black - billed and Yellow-billed cuckoos were obligate brood parasites in the past because such mimicry is unlikely to evolve in a facultative brood parasite.
  • The filamentous fungus Fusarium oxysporum is a soil-borne facultative parasite that causes economically important losses in a wide variety of crops.



Example sentences
  • The adult cowtail stingray of Shark Bay, Western Australia, is a solitarily foraging animal that facultatively groups when resting on shallow, inshore sand flats.
  • In many, if not all, facultatively social bees, ecological factors such as competition for nesting sites and predation seem to promote social nesting, although genetic differences may also underlie social variation.
  • The heterogeneous enrichment among individual worms agrees with reports that this nominal deposit feeder can facultatively filter-feed using a mucus net in its burrow, and that the ability to do so varies among populations.


Early 19th century: from French facultatif, -ive, from faculté (see faculty).

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Syllabification: fac·ul·ta·tive

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