Tuesday, January 12, 2010

Rules of Latitude

This from the Chert Glades Chapter meeting, thanks to Jeff Cantrell of MDC.

Ever notice how Alaska claims bigger mammals than the lower 48 states?  Maybe, just maybe, they are right!  Here are two rules to know.

Bergmann’s Rule  Latitudinal based size differences:  We see this with a large variety of mammals and birds.  Animals of the same species will be larger in their population range closer to the pole.  Example, Canadian moose are larger than moose living in Minnesota.

A good explanation is a larger-sized animal produces less surface area per unit of weight, and the animal loses body heat through its body surface so it just makes sense.  Thus, a bigger animal can tolerate the cold better.

Allen’s Rule:  Mammals in colder climates often have shorter extremities (ears, tails, and legs). It is the same principle as above, basically about body heat. It may really be seen with in different animals instead of individuals in the same species.

Think about the ears of a fennec fox or jackrabbit, for them heat loss is important to survive in a hotter climate vs. a pika with its little round ears.

Note to myself:  After looking in the mirror this morning, it is probably time for me to move to Texas.

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