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Re: Nest predation
Chris Brochu wrote:
>...(behavioral characters) aren't necessarily more
> likely to converge...
True. But I argue that this depends entirely on the specific behavior
and that nest parasitism _is_ more likely to converge (see below).
> The percentage of bird species that parasitize is very, very
> small. Perhaps more behavioral variation would arise if crocs were more
> diverse - we'll never know.
Good point. This would also affect its appearance among non-avian
dinosaurs. Like a sort of balanced polymorphism, this sort of parasitism
might only be possible if there is a relatively high diversity of hosts.
> At what node do you draw the line and say "It's more likely from here
> on up."? As far as I know, no living paleognath parasitizes - one could
> make a case that parasitism is restricted not to birds, but more
> specifically to neognaths. Moreover, IIRC parasitic taxa are not found
> among galliforms, loons, or waterfowl, the lineages thought to be toward
> the root of Neognathae, and so parasitism may be more restricted still
> within Neognathae.
The case I am trying to make is that this particular behavior, while
heritable, may not be appropriate for cladistical analysis; that a
species' immediate evolutionary ecology may be a better predictor for nest
parasitism, and that its appearance may well be somewhat independent of
phylogenetic relationships. Rather, I should say that such relationships
might be ephemeral. In the same way that water acts as a kind of selective
factory for making fish-shaped vertebrates, heavy parental investment may
be a crucial prerequisite for the evolution of nest parasitism. Your
argument above re the low frequency of parasitism in birds is a good one
in favor of potential croc nest parasitism. But it also makes my point
about the inapplicability of cladistics. In contrast to say, bower-bird
nesting structures, nest parasitism doesn't (I'm guessing) have a
long pedigree within clades. (But I don't want to be misconstrued about
cladistics. It is a valuable and illuminating tool.)
> >Likely rapid growth rates of dinos in vegetation mounds
> >needed ventilation ala megapode "taking the temperature" (heat may be the
> >stimulus for that bird's behavior. But carbon dioxide concentration is
> >directly related to heat in these nests). Some dino nests are known to be
> >shallow (Troodon, Oviraptor, and Maiasura).
> So are some croc nests - not all of them build mounds of vegetation.
Right. And a very telling point in favor of my idea that fast embyronic
growth was a prime adaptive advantage made possible by increased parental
investment, is the following paraphrased from Seymour and Ackerman: the
Nile croc (ovipositing in sand) has a clutch size of about 13 kg. whereas
the similarly-sized _C. porosus_ makes a vegetation mound but can only
manage 5.6 kg. S & A believe this is a clutch size suppressed by lack of
oxygen. And if _clutch size_ is restricted by limited oxygen,
so would embryonic growth rate. Compare _C. porosus_ with mound building
megapodes which ventilate, i.e., they, like nearly all other avian
dinosaurs, employ strategies selected to optimize embryonic growth rates.
Anyway, I agree with you that nest parasitism would likely be rare in
non-avian dinosaurs. And I appreciate your patience.