Re: Phylogenetic Correlations (II)

From: Christian Mulder <Christian.Mulder@...>
Subject: Re: [Foodwebs] Phylogenetic Correlations (II)
Date: Mon, 23 Feb 2009 12:29:26 +0100
Message-ID: <OFD89213ED.78545398-ONC1257566.00393E58-C1257566.003F1ED2@...>

> 
> Hi Axel, interesting discussion. I am only wondering on the kind of taxonomic
> resolution of some cited references, like "Sand Beach, California"
> (J.W.Nybakken 1982 as Cohen's web #50).
> It is biologically hard to model, or even to imagine, trophic links between
> (1) debris, (2) plankton, (3) amphipods, (4) Blepharipoda, (5) Emerita
> analoga, (6) Tivela stultorum, (7) Donax, (8) Olivella, (9) Thoracophelia,
> (10) Nepthys, (11) Policines, (12) sea otter, (13) birds, and (14) fishes.
>  Member species of each of these taxa have not trophic roles sufficiently
> similar to warrant grouping them together, but crucial nodes of such a food
> web are missing (echinoderms, for instance). 

Hi Christian,

thank you for the comments.  

You are right that, if you look at each of the taxa more closely, we
will find differences between member species.  But this would not
preclude that species are trophically more similar within taxa such as
those listed above (i.e. mostly genera) than across them.  The
results of Cattin et al. (2004) and Bersier & Kerli (2007) would
suggest this is so.  However, since the question here is slightly
different from theirs, the answer might be different.  If one could
show that it was, this could be an interesting result.

Intuition might somewhat be against the idea that species within taxa
are trophically very similar, if we see species mostly in their roles
as consumers.  As mentioned before, trophic similarity seems to be
stronger for the species' roles as resources.  And the roles of
species as resources might also have been the major motivation for
their grouping in many historical food webs, if we imagine these webs
as being constructed by starting with some higher predators ("sinks"),
and then repeatably asking the question "so what do these guys eat?"
until the sources are reached.

Regarding the missing nodes, I assume you are right about these, too.
Your example "echinoderms" would support the idea that lumping species
taxonomically is a good idea, wouldn't it?

Best,

Axel

PS: Looking at the web cited above again, it appears there were some
spelling errors in the original sources: Nepthys -> Nephtys, Policines
-> Polinices (a theorist's blind guesses)