From: rigg@osnome.che.wisc.edu (Tim Rigg)
Subject: Re: Self Regulating Populations
Organization: University of Wisconsin-Madison, Chemical Engineering
Date: 1 Sep 92 13:36:00
In-reply-to: russ@wpg.com's message of Tue, 1 Sep 1992 17:36:16 GMT

In article <Btwu8I.13q@wpg.com> russ@wpg.com (Russell Lawrence) writes:

   From article <RIGG.92Sep1084651@osnome.che.wisc.edu>, by rigg@osnome.che.wisc.edu (Tim Rigg):
   tr> Ask Rose Frisch.  She specifically states that "poor couples in
   tr> developing countries" are not infertile.  They only had 6 or 7 living
   tr> births which is well below the human capacity.  6 or 7 children is
   tr> hardly infertile.

   Were you assuming that poor people necessarily have low-calorie diets?

No, I was reading the article (perhaps you should give it a try).  A
few lines above my quote, it says 

"For instance, data on growth and reproduction of women in Great
Britain in the mid-1800's show that poorly nourished females, who grew
to maturity relatively slowly (a patern that results in less fat per
unit of lean mass), differed from well-nourished females in each event
of reproductive span. ...[lists events] In that British population, as
in many other populations, poor couples still living together at the
end of their reproductive lives had only six or seven living births.
   Most poor people in developing countries have about that number..."


   tr> I'll concede that fat reduced below the menarche threshold can cause
   tr> amenorrhea in humans. 

   I'm preparing a list of citations that demonstrate the operation 
   of this principle in various mammals and birds.  

   tr> Would you provide the corresponding threshold for deer and the
   tr> likelyhood that such a deer would survive the winter?

   I don't know the corresponding threshold for deer, but it's obvious
   from the anecdotal evidence that such a relationship exists.  Otherwise,
   how would we account for the observations of game management experts
   that increased food supplies enhance fertility.

   The ability to survive through winter would depend on the differential
   between the available caloric intake and the energy stored in surplus 
   fat.  It seems to me that this will vary from region to region, but
   it would clearly be amenable to game management policies.

This our point of disagreement.  Please read that again.  We agree
that lower fat content will lower fertility, even shut it off if it
gets low enough.  We disagree that a stable population of wild game
could be maintained by such a mechanism.

   tr> Please provide your analysis of this situation with documented
   tr> calculations and/or explanations.  I am tired of doing your research
   tr> for you.

   rl> I don't see why you think that research is necessary to answer 
   rl> this question.  If a given habitat produces sufficient calories 
   rl> to meet the caloric requirements for 1N animals plus an offset 
   rl> that's barely sufficient to assure fertility, how/why could the 
   rl> population continue to "explode" as it progresses to 2N or 4N?  

   tr> In the base case, the deer consume 5000N calories.  How many calories
   tr> will be consumed by xN deer?

   Why are you avoiding my question?

Because natural food supplies are much more complicated that a trough
of 5000N calories.  You would have realized that if you wouldn't have
avoided _my_ question.

   tr> Also, is chosing an environment "that's barely sufficient to assure
   tr> fertility" a realistic base case?

   Why should we consider cases where the supply of calories greatly 
   exceeds demand?

Because that is how natural systems work.  There are many different
food supplies.  Some are preferred and some are quite marginal.  As
the population grows, the more marginal sources will be tapped and so
on. 

tim
--
    ...  Then they came for me,
	   and by that time there was no one
	     left to speak up for me. (Rev. Martin Niemoller, 1945)

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