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

Re: Long, long last gasp.




On Sat, 24 Jan 2004, Jaime A. Headden wrote:

> I cannot see how an animal can just survive and the
> other die, to call this "competition." If one animal is hunted out, dies
> by disease, or cannot fly, it is not outcompeted by one organism that
> fails to die of disease, etc., as far as I can tell, in this semantic
> argument.

OK.  So what do you call it?  For sake of argument, assume that zebra
mussel populations thrive because other mussels are limited by predation.
This allows zebra mussels to take all the resources--including
substrate--from the native mussels.  Is this predation or competition.
Surely, the zebra mussels are currently outcompeting local species.  But
immunity to predation is the agent of this success.  Similarly, if
predation-resistant birds evolved, this might allow bigger flocks which
eat the seeds, etc., etc.  This is more than semantics.  Indeed, it is
such a widespread phenomenon that it is surprising we don't really _have_
a word for it.

>   Ah, but one of the points of my argument (the smaller one) was that
> enantiornithine extinction also appears to dwindle at the end of
> Cretaceous as much as pterosaurs, and that there is NO evidence that they
> _could_ compete with each other, thus the idea that each's extinction
> could be caused by the other is very tenuous.

Practically _all_ niche delineations of today are assumed to have been the
result of unobservable "ghost" competition.  If we can't observe it even
in extant species, how can we ever observe it in extinct species.  This is
an unrealistic expectation.  Yet, this doesn't reduce its likelihood.

> One could use the one to
> cause the extinction of the other, but this requires that one survive, by
> whatever means, and that this would not reduce the "body count" by two
> groups, just one prior to the K/T

No.  My hypothesis is that both were reduced by a third group:
neornithines(sp?).

> There was sufficient diversity to argue that ornithurines and
> enantiornithines had exemplative diversity to avoid outcompetition,
> despite arguments contrary to this.

Cool: thus allowing the fait accompli apres le deluge.

> Animals today avoid one another, or
> are prevented from avoiding one another, by either dischronal activities,
> or being separated by geography...

Yes.  But also by past competitive interactions, i.e., niche partitioning.

> tinamous are very similar to  chickens,
> one could argue, and the Gondwanan diversity of large ratites seems to
> "prevent" large neognath cursors,

Yes.  But there was most likely niche partitioning (or geograhical
isolation) among the ratites themselves.