From: russ@wpg.com (Russell Lawrence)
Subject: Re: Self Regulating Populations
Organization: WP Group
Date: Tue, 1 Sep 1992 17:36:16 GMT


Tim Rigg writes:
tr> The author stated that lower levels _can_ prevent fertility.  The
tr> extremely undernourished and relatively fat-free women of some
tr> developing countries show that fertility is not prevented.  It is just
tr> lowered. 

Russell Lawrence writes:
rl> Please name one of these countries and explain why you think that 
rl> the relative absence of fat didn't prevent fertility.

Tim Rigg writes:
[nothing]

rl> Would you mind naming one of the countries, Tim?  

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?

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.

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?

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?  If each deer requires, say 5000 calories/day, 
but has 50,000 calories/day available, then we'd have to conclude 
that the habitat in question isn't overpopulated...  at least 
from the standpoint of food supply.  In such a region, it's 
likely that the deer would build fat and be extremely fertile and 
the herd population would increase.  Needless to say, it would be 
ludicrous for anyone to conclude from such an increase that the 
regulatory principle doesn't work.  

-- 
Russell Lawrence, WP Group, New Orleans (504) 443-5000
russ@wpg.com   uunet!wpg!russ