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Re: Copeing with mammals
On Mon, 22 Nov 2004, MICHAEL HABIB wrote:
> 3) What do we mean by competition at this point? This thread has
strayed such that very minimal diet or behavioral overlap is being cited
as evidence for intense competition. That's not technically wrong, but I
think it'd be more useful to have a slightly tighter definition of what
strong competition entails.
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 species
to survive _without_ direct competition between each other. Yes,
behavioral traits are important for birds v pteros...but not necessarily
in direct competition.
>> "Species don't say: "Adieu small niche...I gotta be big now". They are
>> squeezed out of it by other, more effective clades."
> Actually, they might. Really, body size evolution is very complicated
and the causes for gigantism are not known. Some clades follow "Cope's
Rule", and other do not (which makes it a pretty poor rule, I agree).
There are selective forces/advantages for both being big and being small.
And both have effect in most habitats, I would think. The question is why
any clade--or population--abandons its ecospace? This is like people just
handing over their property...it generally doesn't happen.
>Just for a conceptual example, it is perfectly reasonable to think that a
clade might drift towards larger size because of INTRAspecific
competition (which is being strangely ignored in this thread, I think),
namely that large individuals do better than small individuals within a
species for some length of time.
And as bigger members move out of the small niche, this provides
opportunity for smaller members in the small niche. This is why
G. finches fill up _all_ (many, anyway) the niches usually occupied by superior
competitors on the mainland. I mean, ecospace is valuable.
>...most massextinctions seem to be near in time with abiotic pertubations.
I have just read a paper that claims mass extinctions grade into non-mass