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Animal Ecology and Evolution

Nature volume 128, pages 243244 (15 August 1931) | Download Citation



THIS little book consists of three lectures, “The Regulation of Numbers”, “The Significance of Migration”, and “The Real Life of Animals”. An environment is an entity composed of plants and animals, the species of which are constant. But it is pointed out that the numbers of the different species of animals vary not only in accordance with the periodic changes of temperature, rainfall, etc., but also in an irregular manner. There may be an optimum density for a species and, when its population varies too far from this, the species changes its behaviour. The most obvious change is that of migration into a region which may be very different from its old home, a new habitat. It seems to be an inherent impulse, for the individuals which migrate are often annihilated, without in any way eliminating the impulse in the species when the disadvantageous circumstances which caused it recur.

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