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A facultative parasite is an organism that may resort to parasitic activity, but does not absolutely rely on any host for completion of its life cycle. Examples of facultative parasitism occur among many species of fungi, such as members of the genus ''Armillaria''. ''Armillaria'' species do parasitise living trees, but if the tree dies, whether as a consequence of the fungal infection or not, the fungus continues to digest the wood without further need for parasitic activity; some species even can infest dead wood without any parasitic activity at all. As such, although they also are important ecological agents in the process of nutrient recycling by microbial decomposition, the fungi become pests in their role as destructive agents of wood rot.〔Agrios, George N. Plant Pathology. Publisher: Academic Press 2005. ISBN 978-0120445653〕 Similarly, green plants in genera such as ''Rhinanthus'' and Colpoon can grow independently of any host, but they also act opportunistically as facultative root parasites of neighboring green plants. Among animals, facultatively kleptoparasitic species generally can survive by hunting or scavenging for themselves, but it often is more profitable for them to rob food from other animals kleptoparasitically, whether their hosts are of the same species or not. Such behavior occurs in lions and hyaenas for example, and also among insects such as "Jackal flies" in the family Milichiidae. More intimately, normally free-living microbes may opportunistically live as facultative parasites in other organisms.〔Reynolds Bruce D. "Colpoda steini, a Facultative Parasite of the Land Slug, Agriolimax agrestis" The Journal of Parasitology Vol. 22, No. 1 (Feb., 1936), pp. 48-53. Stable URL: http://www.jstor.org/stable/3271896〕 An example of this in humans is Naegleria fowleri. As a rule this amoeboid species is a free-living predator on microbes, but occasionally it successfully infects humans as a facultative internal parasite.〔http://www.cdc.gov/parasites/naegleria/general.html〕 ==See also== * Parasitism * Parasitoid * Parasitic plant * Obligate parasite 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Facultative parasite」の詳細全文を読む スポンサード リンク
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