There are actually a few different (I think maybe even 5) subspecies of moose. The Yukon-Alaskan being the largest. But the environment doesn't hurt either. Due to the large population of small shrubs and brushes they feed on, as well as large water supply, the northwest is perfect habitat for moose.
The only problem for moose is it's also pretty darn good habitat for bears....
I read something not too long ago that made sense to me. Mammals in extreme cold climates have evolved larger in weight in order to keep their core temperature warm in winter. For example, a moose in Alaska that is twice the weight of a Wyoming moose has less then twice the "surface area" of the smaller variety. Thicker, to insulate innards ( the longer legs probably came about from evolving in deep snow).
It seems to be consistent with: wolves, deer ( Alberta whitetail vs Texas), coyotes, rabbits ( snowshoe vs. cottontail ), and so on. Critters that nest-up in cold weather don't seem to change ( mice, squirrel, etc).
I'm not sure of the source where I read it, but I think it was one of the Wolfe Publishing's mags, "Rifle" or "Successful Hunter".
I've read the same thing, just don't remember where. But look at the Plains Bison that was transplanted to Alaska back in the 50s I believe. It has been reported that each generation is larger than the last. And the Wood Bison that normally lives in the cold areas is bigger than the Plains Bison. Again look at the Alaskian Wolf, much bigger than the ones in the states.
The problem with the "farther north the bigger" theory is that Helsinki, Finland is the same latitude as Anchorage, Alaska, and most of the 100,000+ moose shot in Finland each year (most with 6.5x55 Mausers by the way) are shot considerably north of Helsinki. Nonetheless, the European moose (Alces alces) of Finland are considerably smaller than the Alaska/Yukon moose (Alces alces gigas) of equal or lower latitudes.
Y'all are probably thinking of the biological "rule" called "Bergman's rule" that states:
In a warm-blooded, polytypic, wide-ranging animal species, the body size of the members of each geographic group varies with the average environmental temperature. According to this principle, warm-blooded animals living in cold climates tend to be larger than animals of the same species living in warm climates.
As with all 'rules', it's more of a "guideline" than a "rule"...
Bergman's rule has alot of examples proving it. Another example is the size of white tailed deer in Canada and Whales that deep dive in the ocean to very cold depths. So it's both subspecies and location. location. location. ;D
It's not just body mass but the proportions in limbs and appendages. The ears of the antellope jackrabbit found in the southwest versus the snowshoe hare. Even people are built different, the long legged lanky build of Africans vs the short legged compact build of Eskimos. Rather than evolution though I prefer to think of it as God taking care of his creation.
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