parasitism
parasitism The interaction of species populations in which one, typically small, organism (the parasite) lives in or on another (the host), from which it obtains food, shelter, or other requirements. Unlike a predator, a parasite does not have to kill its host in order to obtain food. Parasitism usually implies that some harm is done to the host, but this interpretation must be qualified. Effects on the host range from almost none to severe illness and eventual death, but even where such obvious immediate harm accrues to the individual host it does not follow that the relationship is harmful to the host species in the long term or in an evolutionary context (for example, it might favour beneficial adaptation in the host species population). Obligate parasites can live only parasitically. Facultative parasites may live as parasites or as independent saprophytes. Ectoparasites live externally on the host. Endoparasites inside the body live body of the host. A partial parasite is a plant that carries out photosynthesis, but relies on its host for other nutrients and needs, e.g., support. Compare COMMENSALISM; MUTUALISM; and NEUTRALISM.
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parasitism
