Higher latitude squamate species always show the reverse of Bergmann's rule. This is a zoogeographical rule that states for any given species, body mass will increase with increasing latitude of that species within it's range. However, with any given snake or lizard species that covers a large geographical area, the adult sizes of individuals within this range will always decrease with increasing latitude, the opposite of Bergmann's rule. This is an inherited trait, breeds true, and it is highly possible that this timber rattler was expressing the basis for this concept. One reason for this smaller size of ectotherms in cooler climates has been linked to the ability to more efficiently thermoregulate. For an ectotherm, a larger body mass may hold heat longer, but a smaller body mass will heat more rapidly and efficiently. This will give the smaller animal the ability to remain more active over a longer period of time than an animal with a larger body mass. This concept has one exception, and that is for some dwarf reptile species found on very small isolated islands. These animals become inherently smaller so as to more efficiently utilize highly limited resources.

Kelly

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