From: russ@wpg.com (Russell Lawrence)
Subject: Re: Self Regulating Populations
Organization: WP Group
Date: Fri, 28 Aug 1992 05:21:43 GMT

Russell Lawrence writes:
rl> As a side-note, would you say that human diseases (AIDS, for instance)
rl> are transmitted more slowly in small towns than in large cities, simply
rl> because the populations are smaller?  If readers were to stop and analyze
rl> the transmission vectors of most diseases, I think they'd come to
rl> the conclusion that the indiscriminant culling of a given population is
rl> *not* going to be effective in preventing the spread of disease, whereas
rl> the culling of infected individuals alone can be quite effective.

From article <1992Aug25.135218.510@spdc.ti.com>, by achenbac@epcot.spdc.ti.com (Jeff Achenbach):
ja> Just a guess, but it would seem more likely that population density, not 
ja> population per se, is the important variable. Diseases with only human 
ja> vectors for transmission will obviously spread faster when interactions
ja> are more frequent.

I don't doubt that deer are social animals, and that they either seek 
out contact with one another or avoid contact with one another in 
accordance with their needs.  Is there any evidence to suggest 
that the number of contacts/capita is diminished when the 
population is indiscriminantly culled?   If not, why would we 
believe the claim that indiscriminant and discriminant culling
are both equally effective in reducing disease?

Jonathan Spencer writes:
js> You should remember that while the wolf (your favourite example) would
js> rather go for a weakling, the wolf pack is perfectly capable of taking
js> healthy specimens. Were it not so, the quarry herd would necessarily be
js> required to keep some percentage of sick specimens for the wolf to prey
js> upon or the wolves would die out...

rl> Are you assuming, perhaps, that wolves consume only deer?

js> The same is true of African dogs,
js> leopards, stoats, weasels, pike, hawks, you name it. They are all
js> capable of taking perfectly healthy specimens of their quarry - they
js> *have* to be.

rl> Is this true?

ja> Yes.  Or at least I have seen hawks, owls, and coyotes take game 
ja> that appeared perfectly healthy.  I've spent many days afield and 
ja> seen very few sick animals.  I have seen countless healthy ones.  
ja> This leads me to believe that the vast majority of wild animals 
ja> are reasonably healthy.  A coyote or wolf would be hard pressed 
ja> to survive if it never took a healthy animal.  If you don't have 
ja> time to go out in the woods and see for yourself, turn on the TV.  
ja> There have been many wildlife documentaries showing predators 
ja> hunting.  Sometimes the prey gets away, sometimes not.  There 
ja> doesn't appear to be an overabundance of sick animals being eaten 
ja> in these films.  

As a long-distance, television observer, how can you tell whether the
prey animals you're observing are sick or healthy?   

rl> Do you have any evidence to prove your conjecture that wolves are capable
rl> of taking perfectly healthy deer?
rl> 
rl> Let's assume, just for the sake of argument, that your conjecture 
rl> is true.  If wolves are capable of killing perfectly healthy 
rl> specimens, what prevents them from simply killing all the deer?  
rl> Do wolves conduct a deer census perhaps, and allot themselves 'x' 
rl> number of deer per pack per annum?  

ja> In most cases, wolves kill to eat. When they are satiated, they don't hunt. 
ja> Most prey species reproduce at a higher rate than predators. When prey 
ja> animal populations drop, a drop in predator density 
ja> follows.  Whether adipose tissue or starvation is responsible, 
ja> I don't know, but if prey population density (including but 
ja> not exclusively deer) gets sufficiently low that caloric 
ja> expenditures to capture it exceed the caloric benefit of 
ja> eating it, predators must relocate, alter their diet, or die.  

How many fawns does a doe typically produce (at most)?  How many
pups does a female wolf produce at most?   [End of theory]

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