Bergmannの規則の例外を含む説明 : とくに鳥類につき

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書誌事項

タイトル別名
  • An Explanation of Bergmann's Rule and Its Exceptions, Chiefly on Birds
  • Bergmann ノ キソク ノ レイガイ オ フクム セツメイ トクニ チョウルイ ニ ツキ

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説明

The Bergmann's rule is currently explained by the advantage of larger body-size in relation to heat loss. There are however exceptions to this rule subject to factors other than temperature. The skylark and woodpeckers in Japan, for example, increase in size north to Hokkaido but decrease again in Sakhalin where the Brandt's Jay is also smaller than in Hokkaido. This may be explained by a concept of 'limit of adaptive temperature zone'. The body-size would be determined by : temperature-activity rate-food intake-metaolic rate-ontogenetic growth. 'Species' are physiologically adapted to a certain temperature zone, within which the rates in the above correlations are increased in lower temperatures. Then, this effect would operate through the course of ontogenetic growth to make the body size larger in lower temperatures, and the grown adults may form a larger-sized population (proving Bergmann's rule). Outside the adaptive temperature zone, animals expend extra energy for reactive control of their body temperature and therefore would become less active (hibernation and estivation are special solutions for extreme conditions) and would take less food, and thus the energy source for growth is decreased. This would affect the ontogenetic growth rate and would cause a smaller-sized adult population (reversed effect of Bergmann's rule). This explanation could therefore be applied as a causative factor both to positive and negative evidence of Bergmann's rule, while the heat-loss rate would rather be regarded as a consequential factor, advantageous for maintaining larger body-size in cooler climate. The disadvantageous small body-size in cool conditions can be compensated adaptively by increased amount of plumage or fur. It is also suggested that in optimum temperature zone, population of a species may become sedentary and tend to become larger, while in high temperature zone the Alien's rule may also become involved. Migratory birds are affected by adaptive elongation of wing length in more northern population (Williamson's effect) and the temperature-growth effect is to be analysed in comparison with other measurements. Various eco-ethological adaptive effects should also be considered.

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