Subject: Re: schooling behaviour

From: [email-masked] (Daniel Shoup)
Date: 17 Jun 1996 13:21:32 GMT

kevin patterson ([email-masked]) wrote:
: I wonder if someone could help me. I am looking for a succint 
: explanation of schooling behaviour in fish. It baffles me; I can 
: understand co-operative hunting beahviour in for instance, orcas, but 
: what advantage is conferred upon say, a ball of tom cod a hundred metres 
: in diameter? Surely the chances of a fish in the interior seeing 
: anything edible must be low? And as far as protection against predators: 
: on a species wide level, wouldn't fewer tom cod get eaten if they were 
: dispersed? In infantry school the first thing they tell you is 'don't 
: bunch up.'

: If anyone can help, please e-mail me at [email-masked]

Actually, the "bunching up" is what provides the antipredator
mechanism.  Most piscivorous fish are highly visual and need to key in
on a single individual to attack.  This is very tough to do in a dense
school.  This causes what is called the "confusion effect" (see
article by Landeau & terborgh, 1986 "Oddity and the 'confusion effect'
in predation" Anim. Behav. 34:1372-1380).  While the predator has no
trouble locating food, its success rate at capturing food drops
tremendously. Hope this helps.

Dan
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---------------------------------                                             
Daniel E. Shoup                                                               
Department of Biological Sciences                                             
Kent State University                                                         
[email-masked]

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From: Sean Clancy <[email-masked]>
Date: Mon, 17 Jun 1996 11:26:55 -0230

> tremendously. Hope this helps.
	Why then do piscivorous fish (such as the North Atlantic Cod) 
tend to display shoaling behavior and "bunch up"?  Also why are fish 
such as herring(Alosa spp.) and capelin(Mallotus(?) spp) found in large 
schools while in the absence of predators?  There are many 
instances in fresh water environment which lack key predatory fish and 
still contain species that shoal (school).  
	Anti predatory defense mechanisms are not the only reasons why 
fish display "bunching up" schooling (shoaling) behaviour.

my $0.02 worth

sean

Why does a dog lick itself?  Because it can!
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Sean Clancy,  BSc.                          __===////====//___    /|
Memorial University of Newfoundland        -  o               ---/|
St. John's,  Newfoundland. A1B 3X9        WWWW }}}------==========|     
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From: [email-masked] (Flconnor)
Date: 17 Jun 1996 18:57:33 -0400

<<<I wonder if someone could help me. I am looking for a succint 
explanation of schooling behaviour in fish. It baffles me; I can 
[snip]
dispersed? In infantry school the first thing they tell you is 'don't 
bunch up.'>>>

Another post mentioned some other reasons for schooling behavior.  As far
as predator avoidance, schooling does decrease the probability of being
consumed in many species.  The enemy rifleman (predator) in your infantry
example has evolved (been trained) to maximize the number of kills without
considering saitiation.  This behavior is not well adapted in a real
predator.  It's the same principle that a good parasite doesn't kill its
host.  A pedator that kills much more than it can consume will eventually
deplete the prey to the point that the predator will starve.  Naturally
evolving predators rarely kill indiscriminantly beyond the point of
saitiation.  Therefore, if you are prey and are in a large group, a
predator will consume some individuals in the group, but most individuals
escape.  If you were a lone prey item encountering a predator, you would
have a higher probability of being consumed than if your were part of a
gorup of 100,000.