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Desert Diary
Culture/Bergmann's Rule


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According to Andy Warhol, everyone enjoys 15 minutes of fame—but some have more. In the sciences, often a person's name is hitched to his discoveries, though this isn't always so great—do you suppose Dr. Alzheimer liked his name associated with a serious mental disease.

Two biologists, however, should be pleased having their names associated with the concepts they developed. Carl Bergmann noted that warm-blooded animals of the same species tended to be less massive nearer the equator, becoming more bulky in colder regions. This is known as Bergmann's Rule. Later, Joel Allen noted that the length of appendages such as limbs and ears tended to be longer in hot climates and become shorter as one travels to colder regions.

Many of our desert mammals and birds follow along with these rules, and a little thought shows why. A small desert animal has fewer cells producing heat and a relatively large body surface to get rid of it, and a long, slender build increases the surface area relative to the volume, just great for shedding heat.
pen and ink


Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.

Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.

Snowshoe Hare Black-tailed Jackrabbit

Allen's Rule. The Snowshoe Hare (left) is a northern creature, most common in the boreal regions of Canada. The Black-tailed Jackrabbit (right) is a creature of the hot plains and deserts. Note particularly the difference in the size of the ears. Snowshoe Hare photograph by Glenn Vargas, © California Academy of Science. Black-tailed Jackrabbit photograph taken and © by Alison M. Sheehey.



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Adapting to Climatic Extremes