From: viking@iastate.edu (Dan Sorenson)
Subject: Re: Closure on Sport Hunting.
Organization: Iowa State University, Ames IA
Date: Tue, 18 Aug 1992 21:38:47 GMT

In <Bt62uE.3B8@wpg.com> russ@wpg.com (Russell Lawrence) writes:

>Thanks for admitting that you don't know the answers.  I hope you 
>won't mind if I continue asking questions of other readers...  in 
>spite of the fact that you're on record as not having any 
>pertinent facts available.  :-) 

	"The wise man knows he still has much to learn."

>Fat tissue is a switch, Dan.  Did you ever wonder why the average 
>fit male human has roughly 10% body fat, whereas a healthy woman's body 
>fat might run around 25%?  In the average american woman, this added fat
>carries an energy surplus of roughly 144,000 calories.   Now what purpose
>do you think this energy surplus might serve?  

	We've already discussed this part, and I agree with all of it.
However, the switch part I disagree with because it implies a binary
condition.  It won't work that way.  One deer will be fertile at 20%,
another will be infertile at 30% due to individual differences.  And,
one cannot hope that it works in all cases at all times.  If it did
work so well, there would never be a starving fawn.  It happens.

>The precise set of mechanisms that allow fat tissue to serve as a 
>"switch" doesn't matter for the purpose of our discussion, but 
>the fact remains that this mechanism inhibits reproduction when 
>food supplies are scarce.  Hence, the argument that mammalian
>populations are limited primarily by death [either from starvation or 
>predation] appears to be unfounded.   

	No, but it does appear that body-fat content serves as mitigating
factor in population control.

>ds> It would lower population growth for one season, at which
>ds> time the present herd population has decreased due to starvation.

>Why would you make such an assumption?  If lower fat content 
>reduces fertility, hence reducing birth rate, don't you think
>diminishing food supplies would _decrease_ the herd size and 
>thereby reduce the threat of starvation?  

	Yes, they will.  What sort of time frame are we talking about
here?  The lack of dampening in this process is what gives us the
growth->starve->growth->starve cycle we know so well.  Since neither
population nor food supplies are constant over a month, let alone a
year, I'd say the factors we mention don't work incredibly well in
the short term.  Over several years, they will serve to keep the average
where it should be, but the data points will fluxuate quite a bit.

>ds> In addition, there will be some young born as the time of conception
>ds> may have been when food was plentiful, and caloric intake/capita
>ds> need not drop in a gentle curve depending on the area the herd
>ds> has to forage in. 

>After you expand this idea, I'll be happy to reply.

	I think I mentioned it once before, so how do you wish for
me to proceed in expanding this idea?  The gestation period in most
mammals is long enough that the available food could diminish quite a
bit between conception and birth.  Thus, you could have fawns born in
the midst of a famine despite the inherent switch we mention above.
In addition, you could have a drought that decreases the population
and then followed by some good rains and plenty of food with little
remaining population.  It will work both ways, and it is not
particularly responsive for the short term.

<Dan Sorenson, DoD #1066 |"There'll be angels on Ariels in leather>
<z1dan@exnet.iastate.edu | and chrome, Ridin' down from heaven    >
<viking@iastate.edu      | just to carry me home." -- R. Thompson >
< ISU thinks I need more education, which they provide for a fee. >