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Re: gigantism as liability
Well, (r-type strategy) sure is common among vertebrates, so the simple
explanation is that the strategy works.
Yes...nature selects strategies that work...therefore all strategies that
work are selected for, valid, good, etc. Beyond the tautology, as you have
argued, circumstances are everything...my complaint is that we don't
consider the circumstances deeply enough in this case.
So it might be argued that mammals have fewer advantages to being large
than sauropods, that selective pressures for large size are not as great
for them. If not, why not? Because sauropods defended their nests; at
this time of the year they likely faced the entire decimation of
reproductive output unless they were large enough to engage in its
This in an interesting hypothesis, but I remain skeptical in that 1) many
dinosaurs that also used an r-type strategy were much smaller...
a) Can't we safely say that most dinosaurs were bigger than most mammals
today, so they were less likely to be able to hide their nests, ergo, the
need for nest defence?
b) I'm not arguing that this strategy is only for big animals. Rather, that
really big animals that can't hide nests need _both_ r-type strategy and
To be more convincing, your model would require stronger evidence of
intense nest protection by sauropod parents...
As long as hypotheses are being thrown around in the article
discussed...nest defence is universal
against defensible predators. And animals are careful about who they will
engage--I forget the bird who defends against other birds but will abandon
its nest if threatened by a hedgehog.
...as well as evidence that giant size would improve nest protection
But the very same hypothesis is always invoked (and in the article)
regarding adult vs. adult
I think we also need more data about the impacts of high- care,
high-investment viviparity in living mammals. The strategy clearly has
distinct advantages, but there are substantial costs as well. The
optimum conditions and size ranges for the operation of such strategies
is, as far as I know, poorly typified (and is further confounded by
phylogenetic history - there are simply no secondarily oviparous
placentals to use as comparisons).
So interesting...I wonder if we still posses silenced shell-making genes?
It seems intuitive that live-bearing and egg-laying should have radical
effects on overall ecology, but I'm not sure if there are data to support
this intuitive sense of things, or not. It might be, for example, that
the net survival of offspring would have been roughly the same for a
giant mammal and giant dinosaur of the same mass, for example, despite
the radical differences in life history. We don't actually have a strong
reason to believe the ultimate numbers would differ wildly - this could
be a case of different solutions, similar effect.
When one considers the extent to which _all_ extant animals go to protect
their reproductive investment, and overlay that imperative on the need to
defend nests, I think this presents an opportunity to envisage some very
different ecological dynamics. Independent of numbers, it is reasonable to
argue that these different dynamics conferred different value on various