Eirik Korsell <eirik at ibm.net> wrote:
>why does small animals have a higer metabolic rate per mass unit than large ones?
To which Martin Brand said:
>Nobody knows, despite this being one of the oldest questions in physiology. There are many theories (but none that everyone accepts). Some of the simpler ones relate to heat loss, which must be part of the answer (you could fry an egg on the surface of an elephant that had the mass-specific metabolic rate of a mouse), but they don't really appear to fully explain the observed size-dependencies.
>Many books address this question. You could look at any recent comparative physiology textbook, or:
>Schmidt-Nielsen "Scaling - why is animal size so important" Cambridge 1984
>Calder "Size, function and life history" Harvard 1984
While it's probably true that nobody knows all the details, the answer
must certainly fall within the general analysis of scaling variations
between organisms, which all have to do with the fact the you cannot
vary any quantity, such as length, while varying its powers (surface
area, volume, etc.) in strict proportion. Why is a rat different from a
scaled up mouse? Why does an elephant have legs that are very fat in
relation to the whole animal whereas a spider has legs that are gossamer
thin? Why can a mouse walk away from a fall down a mine shaft whereas a
horse is likely to be killed by a fall from a height of 2 or 3 metres
(unless it's a steeplechaser that has been trained to land, but even
then falls from a height that a mouse wouldn't care about can be fatal).
Years ago J. B. S. Haldane (or maybe his father, the physiologist J. S.
Haldane) wrote an article called "On being the right size" that dealt
with many of these questions, but I don't remember if it discussed
metabolic rate as such.
Athel
Email: athel at bigfoot.com
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