Hiding in the tundra...[theory?]

[Kenelm Philip]

> Perhaps the extra pressure you mention is caused by water vapor

I doubt that water vapor has anything to do with it. Otherwise the world's
oceans would be covered with high-pressure air masses--rather than breeding
hurricanes...

> I was more interested in 6,000-12,000 feet at +65 F.

Here's a quote from Mani's book: 'Ecology and Biogeography of High Altitude
Insects':

 "In the case of insects, however, the increasing oxygen deficiency of the
air at high elevations does not seem to have any appreciable direct effect.
Most insects are know to be extraordinarily resistant to not only extremely
low atmospheric pressure, but also to rapid alternations of low and high
atmospheric pressure."

 "Lutz exposed millipedes, _Drosophila_, beetles, butterflies and bees to
low atmospheric pressure in the neighborhood of 1/10000 mm Hg for 90 se-
conds without visible harm."

 "Such experimental investigations do, however, emphasize the fact that
insects are not likely to be directly influenced, to any significant effect,
by the reduced atmospheric pressure at high altiutudes in the same way as
Vertebrata are affected."

Insects in these tests seemed to function fine up to elevations of over
17,000 meters--more than twice the height of Mt. Everest. Note that some
species of _Parnassius_ live at 6000 meters elevation in the Himalaya.

> how can I reconcile that with the commonly stated "fact" that if Everest
> were at the same height as McKinley-Denali it would have an oxygen/atmos-
> pheric? pressure equivalent of 3,000 feet higher than present and be
> beyond the human ability to climb without supplemental oxygen?

You presumbly mean 'at the same latitude' rather than 'at the same height'.
I got my figure of 1 millibar from the local Weather Bureau office--but
the difference at sea level is certainly not 10%! However, note that the
gravitational force at a given elevation is greater as you move towards
the poles--and that will decrease the scale height of the atmosphere.
A smaller scale height means the pressure falls off more rapidly with
altitude.

	Now, as regards 'burrowing' behavior. I was referring to the way
arctic butterflies will burrow into the tundra (and vanish) when they are
under one's net. Same thing for scree. When they are being pursued, however,
they will normally escape by flight. Oddly, it was only a couple of weeks
ago that I observed a textbook case of escaping pursuit by abruptly drop-
ping into low vegetation--and this was a _Speyeria zerene_ in Haines,
Alaska, in coastal rain forest habitat. This was clearly a predator-eluding
strategy: the drop was very abrupt just after the butterfly had changed
direction--so that one's eye was led to look past the spot where it
dropped. The same butterfly did this 4 times in row before it finally took
off into the forest.

	As regards butterfly flight, I believe the mechanisms involved are
fairly well known now. They are rather complex--but no violations of
physics are involved. The old claim that "science has proven that the
bumblebee can't fly. The bumblebee, being ignorant of this fact, goes on
flying." is based on a faulty model of insect flight, which assumed the
wings are rigid. They aren't.

	It is quite possible that butterflies could chnage their predator-
escape strategies at high altitudes. But I doubt that lack of oxygen or
low air pressure is the main factor. After all, the same factors would
influence their non-arthropod predators even more severely. I can't run
down _Colias nastes_ at sea level--I wouldn't even _think_ of trying to
run them down at 10,000 feet!

							Ken Philip




 
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