[Taxacom] Ladderising phylogenetic trees

[Neil Bell]

Whether a tree is ladderised or not  has absolutely no influence on what 
it represents, and as long as you know how to read trees it should have 
no influence on how you understand it. The danger is that ladderised 
trees may be read as indicating things that they don't. Ladderised trees 
draw attention to grades of non-speciose groups by placing them next to 
each other, potentially implying relationship, whereas on a 
non-ladderised tree elements of such a grade may be widely scattered. A 
grade is simply an artificially incomplete clade, so any tree contains 
more grades than the ones that the method of representation draws 
attention to. Obviously members of a clade will always occur together 
however the tree is represented. Nonetheless, ladderised trees are 
simply easier to read even if you are not likely to misinterpret them. I 
think this is down to an internal mental process akin to parsing grammar 
when reading a sentence. It's simply easier to rapidly internalise the 
implied relationships if you know that more speciose groups are always 
on one side, just as it's easier to read a language if you know its 
conventions for ordering grammatical elements. Large, non-ladderised 
phylogenetic trees are difficult to read because you have to scan 
backwards and forwards (or up and down) while you are internally parsing 
them. Computer programmers tend to order nested parentheses for exactly 
the same reason.

The merits of different forms of ladderising (e.g. top to bottom or 
bottom to top) are entirely subjective. You like what you are most used 
to, or perhaps what your native written language predisposes you to.


Kristina LEMSON wrote:

Hi everyone
> I am searching for literature in which the authors express opinions on the merits or otherwise of ladderising phylogenetic trees. Although I have found things like "one might like/ choose to ladderise the tree", I have found little that acually discusses reasons for making this decision, or the pros and cons of different forms of ladderising.
> Does anyone know of papers/books where this is considered? Alternatively, does anyone have an opinion  to share via taxacom (or direct email to me)?
>
> Best wishes
>
> Kristina
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-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Neil E. Bell
Postdoctoral Researcher
(Bryophyte Systematics)
 
Botanical Museum
PO Box 7
00014 University of Helsinki
FINLAND
 
email: neil.bell at helsinki.fi
Skype: cryptopodium
SkypeIn : +44 131 2081898
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