From: russ@wpg.com (Russell Lawrence)
Subject: Re: Self Regulating Populations
Organization: WP Group
Date: Wed, 19 Aug 1992 02:39:23 GMT

In article <Bt62uE.3B8@wpg.com> russ@wpg.com (Russell Lawrence) writes:
rl> The precise set of mechanisms that allow fat tissue to serve as a 
rl> "switch" doesn't matter for the purpose of our discussion, but 
rl> the fact remains that this mechanism inhibits reproduction when 
rl> food supplies are scarce.  Hence, the argument that mammalian
rl> populations are limited primarily by death [either from starvation or 
rl> predation] appears to be unfounded.   

From article <RIGG.92Aug18085948@osnome.che.wisc.edu>, by rigg@osnome.che.wisc.edu (Tim Rigg):
tr> I am a bit confused.  Do you mean to imply that prey animals such as
tr> deer can completely self-regulate their population?  

Let's not limit our attention to "prey" animals, Tim.

Can predators self-regulate their populations?  Or, were you 
thinking that their populations would also continue to grow and grow 
and grow ad infinitum?  Would predators require "culling" at some 
point to prevent their populations from ballooning out of control?

Again, the biological evidence shows that fertility drops 
dramatically when fat tissue falls below a particular level.  It 
matters not whether the food supply of a particular mammal 
happens to be forest undergrowth in the case of deer, or mice and 
deer in the case of wolves.  Of course, it's far easier to get 
fat on animal food sources than on tree bark, so fluctuations in 
caloric intake (and hence fertility) are likely to be more 
chaotic among wolves than among deer.   

tr> If deer can self regulate their populations without any predation, do
tr> you have any guesses why the League Against Cruel Sports used culling
tr> by shooters to maintain deer populations on reserves they controlled?

Good question.  If it's true that mammalian fertility drops when 
fat levels fall below a certain point, why do newsreels of 
Ethiopian women show pictures of emaciated, starving women 
alongside emaciated, starving children?  The answer is that such 
women and children live in environments that are environmentally 
unstable.  Eco-systems that have been ravaged by natural or man-made 
disasters (earthquake, war, deforestation, etc) as well as 
eco-systems that depend on the unnatural influx of chemicals 
(fertilizer, water, etc) are unstable, and it's in such unstable 
environments that the likelihood of starvation is most prominent
among all animals...  whether human or non-human.

Getting back to the deer park that you mentioned previously, 
would you say that the reserves in question were ecologically
stable and free from human interference?  Were the deer that lived 
therein dependent on the resources of the eco-system alone or were 
their food supplies supplemented with fat-rich animal feeds and/or
handouts from well-meaning visitors?  

Incidently, in my conversations on this topic, I've discovered
that most americans seem to think that animals begin to starve
when caloric intake drops below the point that permits an animal
to get fat... as though fatness is the only alternative to 
starvation.   In effect, their vision of the problem excludes
a missing middle ground.   At one end of this missing ground,
animals get enough food to survive, but not enough food to
protect them from disease.  At the other end of this missing
ground, animals get enough food to live healthy lives, but not
enough food to maintain fat tissue at a sufficiently high level
to assure fertility.

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