Something I don't understand about RTs

[gpb6845@msu.oscs.montana.edu]

Mickey Rowe wrote:

>  I think you're missing an important point about the RT arguments here.
>  Endothermic animals potentially lose a lot of water via exhalation
>  because elevated body temperatures increase the capacity of the
>  exhaled air to carry water.  Combine that with the higher ventilation
>  rates necessary for maintaining metabolism...  A desert ectotherm
>  shouldn't be expected to lose nearly as much water as a desert
>  endotherm all other things (e.g. RT's) being equal.>> 

Isn't the major difference between endothermy and ectothermy that endotherms 
try to keep their body temperatures fairly constant at about 30-45C by 
metabolising food and that ectotherms try to keep their body temperatures 
fairly constant at about 30-45C by getting energy from the sun?

[ In gross outline what you say is largely correct, but if you graph
  the body temperature of a kangaroo rat and that of a desert
  tortoise, you'll find much larger temperature swings in the
  tortoise.  The kangaroo rat will need to retain its water around the
  clock while the tortoise will mainly have difficulty retaining its
  water in the middle and late part of the day as far as body
  temperature goes.  At night when the ambient temperature drops the
  rat must stoke its metabolic fires (and hence respire more) to
  maintain its temperature while the tortoise' metabolism will actually
  slow down.  That's how I understand things anyways.  -- MR ]

Because of this, wouldn't a desert ectotherm's body temperature be equal to, 
if not exceeding that of the desert endotherm's, thus making them need the 
RT's more?  This is something I really don't understand about the supposed 
law that endotherms need RTs.  Cold-blooded animals don't have cold blood, 
they just get their blood warm in a different fashion than warm-blooded 
animals.  The blood of ectotherms is nearly as warm on average as the blood 
of endotherms, and can seriously exceed the temperatures of endotherms, yet 
they have no RTs.

Why not?  I suspect it's because they're not as important as we've been lead 
to believe, and that their apperent lack in dinosaurs (although this has been 
disputed recently by GSP) means almost nothing, and that the extensive body 
of evidence gathered in the last thirty years supporting endothermy will 
eventually be shown to be correct.

Peter Buchholz
gpb6845@msu.oscs.montana.edu

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