[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Copeing with mammals



> > 3) What do we mean by competition at this point? 

> I don't believe there has to be overlap.  Example: a thistle species
> breaks through a thick layer of mulch.  No other plant can do that.
> Absent the mulch, the thistles and all the other plants are 
> struggling to
> survive.  There is overlap and partitioning and exclusion.  
> Thistles are
> not even doing so well.  Now comes an independent dumping of mulch and
> suddenly the thistle outcompetes all the other plants.  I am 
> arguing that
> predatory regimes affect the speciaion and the ability of differnt 
> speciesto survive _without_ direct competition between each other.  
> Yes,behavioral traits are important for birds v pteros...but not 
> necessarilyin direct competition.

Alright, good example, much appreciated.  I see two concepts to pull out here...

Firstly, you are defining "outcompeting" as simply surviving when others do 
not, regardless of character overlap, relationships, direct effects, or even 
indirect effects.  This makes competition a basic survival/death scheme.  I 
think it's fine, BUT it is not the general concept of competition generally 
used, so this needs to be set out up front.  What you are calling competition 
(or, at least, "outcompeting") I would simply call differential death.  (others 
say differential survival, but I tend to focus on who dies).

Secondly, it raises the basic idea of indirect effects from new 
species/characters entering a region.  This, I think, is a great point.  Where 
John's argument breaks down a bit, I think, is trying to pin down what those 
effects are, because there isn't enough information for that yet.  I personally 
would also keep away from niche space issues.

So this would be my version:

The appearance of birds in the Mesozoic, and their subsequent diversification 
as vertebrate fliers must have affected the ecosystems in which they lived.  
This may have had effects, as yet unknown, on other flying species, both 
invertebrates and vertebrates.  How they interacted is unknown, and effects 
were probably a mix of negative, neutral, and positive.  

I would leave it at that.  This is not very satisfying, but it is consistent 
with known ecology and evolutionary biology.  Saying that bird radiations 
triggered mass extinctions, while a neat idea, goes beyond what is known now, 
but (as I mentioned) could make an interesting study (though certainly a full 
PhD worth).

Oh, and part two:

Birds never achieved body sizes as large as pterosaurs, and pterosaurs never 
reached sizes as small as the smallest birds (as far as we know), which seems 
to be related to differing constraints of flight mechanics.   Other than that, 
relating this to competition seems very risky.

--Mike