Regression - Regression

This refers to the movement of animals back to their original habitat, also known as homing or home migration. Migration in the narrow sense refers to this, and is sometimes used to distinguish it from emigration, which is non-returning movement.

Some homing migrations occur in response to cyclical changes in the environment, such as the tidal migration of the small bivalve mussel, which rides the waves, and the diurnal migration of plankton, which is accompanied by changes in light between day and night. Others are related to developmental stages or annual life cycles, such as the homing of salmon, which return from the sea to the river where they were born to spawn. Seasonal migrations, such as bird migrations and fish migrations, are deeply linked to seasonal changes in the environment and their life cycles. Such relatively large-scale homing migrations are carried out to move from areas that have become unsuitable for life to areas that are suitable due to changes in the environment, such as cold, heat, and dryness, or changes in the animal's own lifestyle, such as reproduction and child rearing, and can be said to be adaptations that allow the animal to live efficiently by utilizing habitats that are distributed discontinuously or heterogeneously.

[Mikio Azuma]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

動物が元いた生息場所へ移動していくことをいい、帰家移動、帰巣移動ともいう。狭義の移動migrationはこれをさし、非回帰的な移動である移出emigrationと区別して用いられることがある。

　回帰移動には、小形の二枚貝フジノハナガイの波に乗る移動のような潮汐移動(ちょうせきいどう)、プランクトンの垂直移動のような昼夜の光の変化に伴う日周期移動など、環境の周期的変化に対応しておこるものと、産卵のため生まれた川へ海から帰ってくるサケの母川回帰(ぼせんかいき)のように、発育段階や生活年周期と関連しているものがある。鳥の渡りや魚の回遊などの季節移動は、環境の季節的変化が生活史と深く結び付いたものである。このような比較的規模の大きな回帰移動は、寒さや暑熱乾燥などの環境の変化や生殖、育児など動物自体の生活様式の変化によって、生活に不都合になった地域から好適な地域へ移るために行われ、不連続に、または異質に分布するすみ場所を効率よく利用しながら生活するための適応といえる。

［東　幹夫］

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