Date: Tue, 3 Nov 1998 10:11:21 From: SCHLAUER@chemie.uni-wuerzburg.de To: cp@opus.hpl.hp.com Message-Id: <aabcdefg3489$foo@default> Subject: Re: sub carnivores
Dear Rich,
> If a plant can attract, capture and
> absorb nutrients from prey then I think it could well be carnivorous
> regardless of whether or not it secretes digestive enzymes.
Judging by intuition, the description above sounds good. But if you
look at the living objects themselves, you will discover that in fact
a great many of them fit exactly the criteria above although they are
usually not regarded as CPs.
Many inflorescences are *sticky*. This serves in the first line the
purpose of pollination by flying insects rather than by wingless
arthropods (increasing the probability of outbreeding). In some
cases, sticky flower parts attach the ripe fruits to animals that
disribute the seeds. Inflorescences do frequently *attract* both the
compatible pollinators and the creatures that want to steal the
nectar, pollen, etc. without effecting cross-pollination. In most
cases where the plant surface is not especially blocked by bark or
impermeable cuticles, *absorption* of externally applied nutrients
can take place.
> If the plant achieves digestion by creating a symbiotic
> relationship with bacteria and or fungi then that works for me.
The bacteria and fungi do in a majority of cases not care what the
plant "intends" to create or not, they are just *present* and almost
ubiquitous. In fact, a true CP is rather one that has developed means
to reduce symbioses with fungi and bacteria (e.g. Droseraceae are
virtually devoid of mycorrhizal associations!).
_Petunia_ is an example of a sticky plant that is accepted as a
fairly clear non-carnivore although it fits all criteria mentioned
above. The only means to separate such examples (in fact the
majority of all plants) from true carnivores is the absence/presence
of endogenous digestive enzymes.
> To me the critical question is: Does the plant absorb nutrients from the
> captured prey and is this "significant" to the plant? Of course
> "significant" is a subjective term and a difficult question to answer -
> much harder than the yes/no answer of digestive enzymes.
This is exactly the problem. Carnivory is not significant in an
absolute sense to any CP (this is different e.g. in holoparasitic
plants). All can survive without animal nutrition. The relative
competitive fitness/reproductive success of CPs may be increased with
carnivory but none of them is really becoming a weed in unsuitable
habitats (they are still not able to compete with _Arabidopsis_ in an
average agricultural desert). I do not know of any example of a CP
superseding any other species in a natural habitat *because of*
carnivory.
The ability to adapt to climatic/edaphic changes is in most cases far
more significant for survival than the ability to be a CP.
So the concept of "CP by significant nutritional benefit" is
theoretically a very beautiful if not a perfect one but it is
almost impossible to test rigorously.
Kind regards
Jan
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