Re: A question on bioenergetics

["Scott Hartman" <scott_hartman@hotmail.com>]

Martin,
    It is true that energy demands scale to a coefficient lower than 1 as 
mass increases; this is true for a number of reasons, including increased 
locomotiove efficiency in larger animals and (in endotherms anyways) the 
reduced surface area to mass ratio in larger animals (less heat needs to be 
generated because less is lost).
    Many authorities disagree, however, with the idea that ectotherms scale 
to a significantly different metabolic coefficient.  I'm at the museum now, 
so I don't have my technical library, but I believe that if you peruse 
Reid's paper on dinosaur energetics in The Complete Dinosaur he presents the 
opposing view point, and references some papers on the subject.  Data in 
papers (e.g. Spotilia et al.'s papers on modeling dinosaur thermal 
dissipation) that suggests that "reptilian" and "mammalian" metabolic rates 
should converge all lack good data on large reptile metabolics.
    Of course, this isn't entirely the fault of the researchers.  There 
aren't a lot of 2 ton reptiles running around to serve as data points.  
Still, most of these papers use only sea turtles as a representative of a 
large ectotherm.  This is a really bad idea, since sea turtles may have an 
elevated metabolic rate, and are insulated by  a combination of their soft 
shells and generous fat deposits, and are vastly removed phylogenetically 
from the other members of the published data sets (which are usually small 
lizards).
    It would be far more telling if similar data were available from komodo 
dragons and could be plotted with data from monitor lizards of other size 
ranges.  Unfortunately, _Varanus komodoensis_ is not the most congenial of 
test subjects, which has tended to discouraged proper investigation to date. 
 Still, the data needs to be collected before anyone can make a case for 
the metabolic rates of large endotherms and ectotherms converging.
    The prevalence of this hypothesis (speculation?) of metabolic 
convergence presented in technical papers and textbooks alike should serve 
as a cautionary tale about accepting ideas without being familiar with the 
data.

Scott Hartman

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