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Re: What is an "active ectotherm"?



At 12:37 PM 10/9/96 -0500, George O. wrote:

>Do fish count? Water has a much higher specific heat than air and is a much
>more effective cooling agent. 

        If I recall specific heat correctly, it is irrelevant in this case.
If the fish were surroundeed by cold Fritos(tm), it would get just as cold.
What matters is that there is a temperature differential which is not going
to go away, thus the fish loses heat.  If the fish were in a fish tank, yes,
perhaps being in a subtance of lower specific heat would make a difference,
but not in the ocean.
        In *air*, water is a spiffy coolant, though.  Come to Lubbock, you
can find out firsthand!

>Yet many fish can contrive to swim perfectly
>well through a medium whose temperature would kill an unprotected human in

        Can anyone briefly explain how fish survive when they are
ectothermic?  I know that they have a more stable environment, but that
environment is going to almost always be less than optimal for maintaining
the chemical reactions which sustain life...

>It seems perfectly clear to me that endothermy did not develop overnight.
>Since it seems to be an intricate kind of physiology, it surely evolved in
>stages, over quite a few millions of years. Perhaps active ectothermic
>dinosaurs represent such an intermediate stage or stages in the development
>of true avian endothermy. Perhaps the question we should be asking is, Why is
>there endothermy at all?

        IMHO:  there is ectothermy for animals which will not pay the price
for the advantages of an endothermic metabolism.  I would like to see more
people throw away victorian attitudes and consider the possibility that
maybe endothermy isn't such a hot thing (for you Bonnie...).  Maybe it
happens when it is needed.  I don't see why it has to be so all fired hard
to evolve.  Perhaps it comes about when the need arises.  If the group which
develops it radiates, then perhaps this puts selection pressure on other
animals to become ectothermic as well.  Perhaps it is hard to go back once
you've gotten to it, and animals niches that worked well with endotherms
have ectotherms by default.  It's all very theoretical, of course, but if
you're going to say things like "it surely developed in stages" and "over
quite a few million years", I'd like to hear some back-up.
        Wagner
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| Jonathan R. Wagner                    "You can clade if you want to,     |
| Department of Geosciences              You can leave your friends behind |
| Texas Tech University                  Because your friends don't clade  |
| Lubbock, TX 79409                               and if they don't clade, |
|       *** wagner@ttu.edu ***           Then they're no friends of mine." |
|           Web Page:  http://faraday.clas.virginia.edu/~jrw6f             |
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