Re: Gargling galahs!

[Stan Friesen <swf@ElSegundoCA.ATTGIS.COM>]

 From: Colin McHenry <s172579@student.uq.edu.au>
 > > > My own suspicion is that, as in, say, ostriches, the dinosaurs were 
 > > > R-selected as eggs and K-selected as chicks ...
 > >
 > >Or, mor precisely, a hybrid stategy. 
 > 
 > As far as I can recall my ecology lectures, 'r' and 'k' selection are
 > properties of a population, and do not generally vary with respect to the
 > age of an organism. 

Exactly.  That is why I "corrected" the above to "hybrid strategy".

That is valid because r and K selection are end points of a continuum.
..
 > 
 > >On the other hand, the evidence from the Texas Chasmosaurus
 > >mass-death site is that ceratopsian herds were mixed-age, ranging
 > >from very young to full adult.  his suggests parental care, and
 > >supports mixed-strategy reproduction in at least Chasmosaurus.
 > >.  
 > 
 > Not necessarily; if mortality is heavily biased towards younger age (and
 > therefore smaller size), then once past these dangerous early years the age
 > classes of the population will be of roughly equal size (in terms of
 > numbers), all the way from juvenile to adult. 

In fact the site was biased *against* small individuals.  All of the
small skeletal elements were badly crushed, but there were rather
alot of them. The smallest size class represented by fragments was
well below a "juvenile" in size, and closer to a yearling, or younger.

Also, the adult size class actually had the *smallest* estimated
number of individuals (only three of four of the specimens were adults,
there were at least as many subadults, and a large, undetermined,
number of smaller individuals).

 >  If these ages classes mix
 > into herds (this may be more probable with herbivorous species) then the
 > pattern you describe will result.  If the adults are defending their nests
 > (and even new hatchlings) then the herd (or at least the parents) aren't
 > going to be too far away,  giving the young animals a chance to join up with
 > the herd.  This doesn't necessarily imply parental care of young once out of
 > the nest - the only protection would be as part of the herd.

This is quite correct. But the herd membership appears to have started
within the first year of life - unlike in Maiasaura where herd the
juveniles appear to have stayed in separate herds.

swf@elsegundoca.attgis.com              sarima@netcom.com

The peace of God be with you.