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Re: Sauropod browsing energetics



On 3/24/2011 6:43 PM, Scott Hartman wrote:

That misses the point; to establish a selective pressure favoring a
longer neck you have to show the neck itself is energetically
beneficial; you have to hold the other parts of the body the same
(otherwise you're arguing over whether there's an energetic benefit to
a whole host of other changes).  That means the two animals cannot be
equal in mass, because the one with the longer neck HAS to mass more.

That is not true -- the problem that evolution is "trying to solve" in animals that trend toward maximal size is this -- what shape allows the maximum mass to be fed, which equates to what shape allows the most biomass to be harvested ?

Comparing the efficiencies of various designs (i.e., morphologies) at equal mass is entirely justified.

If you have to
walk anyways between bites, then a long neck is even less useful for
browsing.

An environment wherein an animal that can swing it's head in an arc w/ a radius of 9m and angle (arbitrary number alert) of 60 degrees, yet find only one bite per step, is going to demand a *lot* more than one step per bite on average from a minimally necked animal...

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.

Some things we know -- e.g., as size increases w/in a given body-style, the total mass of food that must be ingested per day to survive increases. Also a long neck unquestionably means you can gather not only (much!) more browse per step, but also more browse in a day, all else being equal. Therefore you can be bigger than your cousin who has the short neck, and that can be well worth any cost.

One thing often missed in the long vs short relative-to-harvesting-biomass discussion is this -- grazing animals are not likely grab a bite in mid-step -- even a hungry cow in heavy pasture takes a step, goes munch, munch, munch, often in an arc -- then takes another step. Taking a bite while your head is in forward motion is just too damned hard to do.

I think the whole debate is a question in search of a problem. With a really long neck, you can not only reach browse unattainable to shorter animals, but you can take a step and then go munch, munch, munch, munch, munch, munch, munch, munch, munch, munch, munch, munch, munch, munch, munch, munch, munch, munch, munch, munch, munch, munch, munch, munch, munch, munch, munch, munch, munch, munch, munch, munch, munch -- step, ...

The above assumes that size was a crucial advantage to sauropods, oph course.

There is indeed in theory a size at which the neck is "too costly", but it is obviously more than 9 or 10m, because necks evolved to that size.