Re: An alternative to ST and AAT
Gerrit Hanenburg (G.Hanenburg@inter.nl.net)
Fri, 1 Nov 1996 10:21:34 GMT
Paul@crowleyp.demon.co.uk (Paul Crowley) wrote:
>No, it's not just speculation. Ecological niches get filled.
But ecological niches cannot be identified independently of the
species that occupy them,and that makes it impossible to say into how
many niches a certain ecological space can be divided.
The African savanna supports numerous sympatric bovid species but it
is impossible to say if there is not room for yet another terrestrial
herbivore. Ecological space is not like a box filled with apples ("a
picture held us captive" ;-). It is dynamic and multidimensional,and
interspecific competition is only one factor influencing it. The idea
that an arboreal species cannot evolve to occupy a (semi)terrestrial
niche because it will be driven back into the trees by what's already
there is a very simple,impoverished view. Adaptive radiations (of
which cercopithecoids and bovids are examples) clearly demonstrate
that there are numerous vacancies.
>The terrestrial primate ones are occupied by large variety.
But that doesn't mean terrestrial ecological space is saturated.
>It's very hard to see how a gibbon or an orang or other purely
>arboreal primate could establish itself on the ground in a new
>niche in the face of such competition.
As long as there is a resource to be exploited,even if it is one
that's already exploited but not exhausted by the terrestrial
"professionals",there's an opportunity.
>Further, purely arboreal species tend to become very specialised
>with particular adaptations that virtually debar the adoption of
>a terrestrial role. Typically these include a degree of
>clumsiness on the ground that amounts to an inability to make
>effective progression.
That doesn't mean a terrestrial niche is inaccessable.
You have to specify effectiveness in relation to goals.
Chimpanzees are quite "clumsy" on the ground compared to ungulates,but
that didn't prevent them from becoming semi(terrestrial).
>> > The niche would almost certainly have been already filled.
Like a bottle with water.
Gerrit
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