Question

Is the metabolic rate and size inversely related?

Answer 1

http://www.biog1105-1106.org/demos/105/unit3/metabolicrate.html

Answer 2

For endotherms , the smaller animal seems to have a higher requirement for oxygen per unit gram , a higher blood volume for its size, Higher requirement for food , higer pulse rate and higher breathing rate than larger animals. This inverse relation can be explained by considering the fact that smaller animals have a higher surface ratio than larger animals and hence heat is lost more easily by smaller animals than larger ones and hence they require more energy for maintianing a stable temp than larger animals . When we consider the body mass of smaller animals , they will have a higher percentage composed of structural materials (Bone , muscle )as opposed to reserve materials (fat, glucose reserves) and it takes lot more effort to maintian strutural materials EG;- more energy to maintian muscle than fat.

This relationship is summerised by a law called Kleiber's law.
R = C*((M)^(3/4))
Where R = rate ( metabolic)
C= constant
M=mass of the organism
This is not an all inclusive answer .... and researchers are still trying to find underlying causes for this inverse relationship.
The more you look into it , we can see that theres a lot of factors that needs to be taken into consideration to explain this relationship besides the simple surface area hyppthesis.
http://en.wikipedia.org/wiki/Kleiber's_law