Date: Fri, 12 May 2000 13:47:13 +0100 From: Paul Temple <paultemple@ecologycal.demon.co.uk> To: cp@opus.hpl.hp.com Message-Id: <aabcdefg1518$foo@default> Subject: Re: Carnivorous Bromeliads
>For those with a particular interest in carnivorous Bromeliads,
Yes, that's me!
>a very interesting scientific work ... published recently ...also
indicates that Puya >raimondii may benefit from decomposing birds,
impaled by spines on its foliage
>(from indicated references)!
Now I just HAVE to read this to see if I am referenced. A very long
time ago I wrote an article (for the UK CPS I think) in which I
postulated that some desert spined bromeliads would be potential
candidates for carnivory. The logic was simple. They live in nutrient
poor environments. There is a ready supply of nutrient in the form of
animals. But most importantly, Puya has spines that point backward.
For those that don't know Puya, imagine a sphere of outward pointing
daggers where each blade has spines along each edge. If the plant were
intent on protecting itself it would point all spines outward, not just
those at the leaf tips.. But no, only the leaf tip spine points outward
(of course!), while all the others point inward. Field observations
show that the inward pointing spines are responsible for the capture of
birds.
Try this experiment - find a Puya, try and touch the stem by placing
your hand between the spined leaves. Easy wasn't it? Now take your
hand back out!!! You will not succeed without at least injuring
yourself, possibly suffering some serious damage. It's unavoidable that
several spines will lock into your flesh and you'll need to pull hard
(don't it will create a bad tear) or use your fingers to carefully
remove each spine, one at a time. If you were a feathered bird (as
opposed to any other type of bird), you'd have a devil of a time getting
back out without spines and feathers becoming attached. Same would
probably go for rodents whose fur would easily becoming attached. In
both cases, the sines would also easily tear into the animals flesh with
little hope that the animal could disentangle itself.
At the time I wrote this, I believed I was the first to postulate that
desert bromeliads (Puya but possibly also related genera) could be
carnivorous and I think I suggested it should be researched to find out.
So, based on the above, I postulated that Puya could be carnivorous. A
rather unkind gentleman responded by riduculing my article. I shall now
look up who he was - maybe it was one of you!!!
If anyone can find my old article (I'll look too) I'd be interested in
knowing if David H. Benzing references it (or me) or if any of his
quoted references pre-date mine.
He who laughs last laughs loudest!
(Since we now have more people researching CP's, I'll restate another
point that I think has never been researched. Cephalotus is black
inside the trap with windows in the trap wall that allow sunlight to
fall on the water pool within the trap. It is suggested and generally
assumed, if not accepted, that this in total, ie. trap and windows and
black trap linng, is an adaptation that acts as a lure to trap prey.
Theoretically, as the suggestion has it, the light passes through the
"windows", shimmers on the water within, and fools the prey into
wandering in toward the light. (This reminds me of the film Potergeist,
which is of course a piece of fiction!)
I find this quite unreasonable. In other plants with windows,
Sarracenia and Darlingtonia, the prey is assumed to be lured toward the
windows themselves through which the light enters the trap. I'm not
sure there is proof or that it is provable, but certainly it means that
the black colouration of Cephalotus is unnecessary. Certainly no
shimmering pools are required in Sarraceniaceae. In any case, I
consider the Cephalotus trap would be poorly designed if a prey
teetering on perhaps the most important decision of its life was allowed
to decide between so many options; go back out toward the strongest
source of light, go towards the windows or go towards the reflections.
So, why be black inside. Well I think it could be to act as a solar
oven. The light entering Cephalotus through the windows could be
allowed to fall onto any part of the inner trap, not just the water
within it - which incidentally makes the windows and black lining
functional from dawn to dusk (good film that!). A black surface would
be better at absorbing this light, and the heat therein. And a heated
trap would logically be more efficient at digesting the prey that fell
into it. Side effects of a heated trap might be expected to include an
enhanced aroma that would better attract prey toward the aroma source (I
really am worried by these twinkling pools that mesmerise prey) and even
provide a heat source that on its own would be a potential attractant to
invertebrates (heat would be an interesting addition to the list of
attractants found in CP's) and that could be found both by its sspectrum
and by the actual level of radiant heat produced.
I don't know how cold it is in the area in which Cephalotus lives. But
if it were cool at night then the trap's design would be very efficient
at quickly raising temperatures during the daytime. But cold is not
necessarily a pre-requisite to support the proposition. Even if it
isn't cold, such heated digestion would be more efficient than, say,
using microbes to assist. Microbes would need to share the nutrient (a
symbiotic relationship) whereas with a solar powered digestive
mechanism, the plant could rapidly access the nutrient without any need
to share it.
It's just a fanciful thought someone might want to ponder on.
Cheers
Paul
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