ECOLOGICAL THEORY and SPECIES DISTRIBUTION JodyLee Estrada Duek, Ph.D. With assistance from

Heat Loss Consider heat loss in very cold climates. Most heat is lost near a body's surface. Therefore, the less surface area a body has relative to its total size the less heat it will lose from its surface. It happens that of all the geometrical forms in nature, the one with the least surface area relative to its total size, or unit volume, is the sphere.

Climate Matters This means that if you live in a cold climate you will find a certain advantage in being somewhat spherical -- being short and thick -- which is essentially the case for, say, walruses, Snowshoe Hares, and Eskimos. The Black-tailed Jackrabbit at the upper left and the Arctic Hare at the upper right clearly take advantage of this phenomenon. – The Black-tailed Jackrabbit, a resident of hot, arid areas, has long ears, long legs and a longish head. – The Arctic Hare's ears are much shorter relative to the head size, plus the head itself is more spherical, and the legs are relatively shorter than the Black-tailed Jackrabbit's.

ALLEN'S RULE certain extremities of animals are relatively shorter in the cooler parts of a species' range than in the warmer parts. extremities means arms, legs, ears, snout or nose Coyote legs, some bird legs

BERGMANN'S RULE It's also a matter of basic physics that the larger a sphere, the less is its surface area relative to its total volume. Therefore, large balls lose heat more slowly, relative to their size, than small ones. Therefore, animals tend to be larger in cold areas than in tropical ones. Bergmann's Rule asserts that geographic races of a species possessing smaller body size are found in the warmer parts of the range, and races of larger body size in cooler parts.

GLOGER'S RULE Turning from spheres, Gloger's Rule states that dark pigments increase in races of animals living in warm and humid habitats. among the animal species supporting this "rule" is humankind – Skin cancer and melanin – Vitamin D and melanin Think of the red-tailed hawks in S. Arizona that are mostly very light in color

THE EGG RULE With special reference to birds in the Northern Hemisphere, the Egg Rule states that the average number of eggs in a set, or clutch, laid by songbirds and several other kinds of birds increases as one moves north in latitude. This probably evolved to balance the fact that in the north songbirds may be able to raise only one brood per season, while farther south, two, three, or more broods may be possible. Doves and quail in S. Arizona can “serial clutch” 4 or 5 times a season