"Representative Trantis"  wrote in message
news:...
> On the whole males are larger than females. The only exceptions are those
> animals which live close together and therefore have increased competition
> between males for females.
> 

Strong competition between males for females is a major factor
*promoting* large males.

> Humans are a good example of this, so much so that we tend to think of all
> males being bigger.
> 
> Humans (And various primates)
> Bulls
> Dogs?
> 
> Does anyone know the complete list of species which have larger males, and
> if it's a big list then a summary of many commonly known animals?

I don't know of a list, but I do know that the elephant seal has the
greatest sexual size dimorphism of the mammals.

Because of a fundamental asymmetry between males and females, stemming
from the initial asymmetry in gamete size (anisogamy), females are a
limiting resource and males are exploiters of this resource.  A mated
female generally doesn't increase her number of offspring as she gets
more matings, and often matings are harmful for females.  A male's
success (number of offsrping) is, however, approximately proportional
to the number of matings he can get.  This is Bateman's Law.  It means
that females generally do not need to compete for males, but males
generally need to compete for matings with females.  If winning fights
allows a male to fertilise more females, and if being big helps a male
win more fights, then big males will tend to be favoured; hence the
dimorphism.

There are exceptions though, because the above conditions will not
always be fulfilled.
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