Good morning morphometricians
I am a PhD student studying morphology of lacertid lizards in the
Iberian Peninsula and for the last year I've been trying to apply GM for
my investigation. Although I've passed a year trying to figure out how
GM methods could be applied to my lizards, there are still some issues
that I'm not very sure about, no matter how preliminary they might seem.
I hope someone here might help me.
I was wondering if there is some way of putting into numbers variability
from landmark data. Intuitively I would say there must be because that's
what they were developed to do, but I'm not sure which of the parameters
calculated during the analysis would be a measure of that. In detail:
a) Is there a way of putting into numbers and testing which of the
landmarks in a sample present more global variablility ("move" more)?
Would the variances (S, Sx, Sy) around landmarks given by the report of
tpsRelw be a measure of that?
b) When comparing groups within a sample, is it correct to evaluate
local differences by examining partial warps independently? I know PWs
are correlated and should not be separated for statistical analyses, but
is there some way of quantifying and examining very local differences?
c) Again when comparing groups within a sample, is there some way of
evaluating which are the landmarks that contribure more to the observed
differences? For example, when comparing male to female lizards I have
run a canonical analysis on PWs and calculated canonical scores. Then I
regressed shape variables to the canonical scores in tpsRegr to view the
shape changes. When selecting to view them as vectors instead of
deformation grids, I can see that some vectors are notably "longer" than
others, but what is the variable that expresses the length of these
vectors? I suppose it must be something related to the mean Procrustes
Distance for each group (sex in my case), but I'm not completely sure
about it.
I'm sorry if this sounds too elemental, but passing from mathematics to
the biological application of GM seems to be quite a step to take after
all.
I'd be very thankful for any suggestions on the above problems.
Cheers
Antigoni
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Antigoni Kaliontzopoulou
Centro de Investigação em Biodiversidade
e Recursos Genéticos (CIBIO/UP)
Campus Agrário de Vairão
4485-661 Vairão
PORTUGAL
Herpetologia, Dep. Biologia Animal (Vertebrats)
Fac. de Biologia, Univ. de Barcelona
Av. Diagonal 645
08028 Barcelona
SPAIN
tel: +351 91 3086188
mail to: [EMAIL PROTECTED]
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