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The dear enemy effect is an ethological phenomenon in which two neighbouring territorial animals become less aggressive toward one another once territorial borders are well-established.〔Fisher, J., . Evolution and bird sociality. In: ''Evolution As a Process'' (Huxley, J., Hardy, A. and Ford, E., eds). London, Allen and Unwin. pp. 71-83〕 As territory owners become accustomed to their neighbours, they expend less time and energy on defensive behaviors directed toward one another. However, aggression toward unfamiliar neighbours remains the same. Some authors have suggested the dear enemy effect is territory residents displaying lower levels of aggression toward familiar neighbours compared to unfamiliar individuals who are non-territorial "floaters".〔Bee, M.A., (2003). A test of the "dear enemy effect" in the strawberry dart-poison frog (''Dendrobates pumilio''). Behavioral Ecology and Sociobiology, 54: 601-610〕〔 The dear enemy effect has been observed in a wide range of animals including mammals, birds, reptiles, amphibians, fish and invertebrates. The behavioural effect can be modulated by factors such as the location of the familiar and unfamiliar animal, the season, and the presence of females. The dear enemy effect is the converse of the nasty neighbour effect in which some species are more aggressive towards their neighbours than towards unfamiliar strangers. ==Function== The ultimate function of the dear enemy effect is to increase the individual fitness of the animal expressing the behaviour. This increase in fitness is achieved by reducing the time, energy or risk of injury unnecessarily incurred by defending a territory or its resources (e.g. mate, food, space) against a familiar animal with its own territory; the territory-holder already knows about the abilities of the neighbour, and also knows that the neighbour is unlikely to try to take over the territory because it already has one. 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「dear enemy effect」の詳細全文を読む スポンサード リンク
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