Re: Extinction

["Larry Febo" <larryf@capital.net>]

-----Original Message-----
From: TRUETT GARNER <DINOBOY@worldnet.att.net>
To: sarima@friesen.net <sarima@friesen.net>; Tommy Tyrberg
<tommy.tyrberg@norrkoping.mail.telia.com>
Cc: jbois@umd5.umd.edu <jbois@umd5.umd.edu>; dinosaur@usc.edu
<dinosaur@usc.edu>
Date: Wednesday, March 29, 2000 9:46 AM
Subject: Re: Extinction


>
>
>> >Or do you simply attribute the whole of the Late Pliestocene/Holocene
>> >extinctions to human action?
>> >
>>Yes, though it is possible that climatic stress may have rendered some
>>animal population more vulnerable to human predation.
>
>Actually, I suspect the combination was a major factor.  Also some of the
>Late Pleistocene extinction in North America appear to have *preceded*
>human arrival here, at least based on the dating of finds in the La Brea
>Pits here in LA.  (Even though the peak extinctions occurred shortly after
>our arrival).
>


I never could understand how  "climate" could be considered a causal agent
in extinction. I mean,....most organisms are quite capable of migrating to a
more amiable enviorn , ...right??? Even trees have shifted their range north
to south in response to the various phases of the ice age. OK,...I can see
an extinction by climate change perhaps in a species confined to a
geographically isolated region,(an island perhaps). But, I can`t see this as
a reason for any large scale extinction involving many groups of organisms.
Extinctions seem to be the result of sudden, drastic changes to which the
organisms in question do not have time to adapt by natural selection. Man is
such an agent of drastic change. Another example would be the interfaunal
exchange that took place between North and South America. One of the best
proposed agents of dramatic and rapid change would be an impact by an
extraterrestrial body! Again, the key here is a >rapid< enviornmental
change.

I don`t know much about La Brea, but I can`t see how any determination of
extinction by climate change can be made by studying one site alone. Sure,
one may see that a species was in decline in that area. Sure, one can also
see that climate was perhaps "deteriorating" in direct correlation at that
particular site. But what is to say that the species in question didn`t just
migrate out of there?