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

Re: Sauropod browsing energetics



On Wed, Mar 23, 2011 at 4:23 PM, Don Ohmes <d_ohmes@yahoo.com> wrote:

> There is a practical limit to the amount of biomass per unit area a given
> habitat can produce. If your absolute daily nutritional needs are higher
> than can be produced on the maximum area your mouth can access in a day, it
> really does not matter how cheaply you get by on a mass-specific basis.

True, although to be fair they authors were attempting to hold
resource distribution constant (and fairly plentiful).  If you have to
walk anyways between bites, then a long neck is even less useful for
browsing.

> An economic analogy would be -- 1) assume I weigh 1000 kgs, and can feed
> myself for a measly one dollar per kilo. 2) Assume you weigh 1 kg, and you
> have to spend 100$ per kilo to live.
>
> I would seem to have a big advantage.
>
> But if the maximum allowable daily wage is capped at 900$, I will definitely
> starve at the rate of 100$ per day, whereas you *might* not, even though
> your mass-specific expenses are much higher than mine.

I agree, but carrying capacities obviously can't be that strict or
else we don't have sauropods at all.  It's not that I don't appreciate
the analogy you're making, but I'm not sure that the rule you're
suggesting will hold in a useful manner once the black and white issue
of 100% negative selection is lost for a more normal selective regime.

> This is why I think that "walking" vs "standing still" scenarios almost are
> not relevant when talking about very large animals and food acquisition --
> when equal average velocity, mass and 'cutter heads' (i.e., cranial
> morphology) are given, long necks (or trunks) can simply access a larger
> area per unit time than short ones can.

This I agree with, but when talking about browsing we're back at the
question of whether any increase in access per unit time offsets the
cost of having a neck.  If not then it's an incidental benefit (or
perhaps a mildly reaffirming pressure) but not a significant positive
selective force by itself, which is what the authors claimed.

-Scott



-- 
Scott Hartman
Scientific Advisor/Technical Illustrator
(307) 921-9750
www.skeletaldrawing.com