Re: Copeing with mammals

[MICHAEL HABIB <habib@jhmi.edu>]

A couple of personal thoughts of some limited relevance (insert "grain of 
salt"):

1) I do not like "niche space" concepts.  Never really have.  It creates an 
abstract species territory concept which does not seem to have much biological 
reality.  Regardless, be careful with terminology and appropriate evidence when 
using niche space arguments.  Most niche space theory has not been tested 
carefully, and while it is a great mental exercise, it can become a problem 
quickly.

2) Niche spaces, if there is such a thing, stay empty very often.  Do not 
assume that the pterosaur niche was ever filled, just because other flying 
animals diversified during and subsequent to pterosaur extinction.  
Incidentally, this is why timing of diversification/extinction is not strong 
evidence, taken alone, of direct replacement.

3) Competition is an individual-level process.  The most intense competition is 
presumably among individuals of the same species, which share a great number of 
characters (by definition).  To understand the evolution of characters, be it 
size, wings, endothermy, or anything else mentioned on this thread and in this 
list, it is very important to remember that directional selection 
intraspecifically can produce extreme character changes and species 
divergences.  This has been written on at length and studied experimentally 
many times; reference citations are not needed here, but I am happy to supply 
some to interested parties, as always.  This doesn't mean that species 
competition should not be discussed, only that the underlying process has to be 
kept in mind.  There have been some great ideas on this thread, but some have 
forgotten how competition is really working.

--Mike