Allen's rule


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Allen's rule

a rule stating that in warmblooded animals (HOMOIOTHERMS) there tends to be a reduction in size of protruberant parts of the body (such as legs, bill, tail) in populations living in cooler climates; for example, within some species of birds, such as the redshank, the length of the bill is reduced. This size reduction is an extension of BERGMANN'S RULE and is also a mechanism to reduce heat loss. The rule was devised by J.A. Allen in 1877.
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Allen's rule states that endotherms inhabiting colder climates tend to have shorter appendages than those of the same species in warmer areas.
The research validates a 133-year-old ecological theory called Allen's rule, which predicts that animal appendages like limbs, ears, and tails are smaller in cold climates in order to minimize heat loss.
Biologists have Bergman's and Allen's Rules, which predict reduced surface area to body size and shorter limbs in colder environments," says Higgins.