-------- Original Message --------
Subject: “Quantitative description of within-group variation to compare
among groups”
Date: Thu, 18 Jun 2009 10:28:02 -0700 (PDT)
From: Henrik Kusche <[email protected]>
To: [email protected]
Dear Morphometricans,
I am a diploma student and relatively new in the vast field of
geometric morphometrics and I would like to ask your advice:
I am assessing the variation in body shape of a tropical fish species
complex from 8 different lakes. My approach is based on 15 shape
encoding landmarks on the fish body and I use MorphoJ in order to
analyse my dataset which itself is based on .tps-files. The data are
corrected for allometry using residuals after the regression of size
and shape. Based on a CVA, I can find a distinct morphology for the
fish of each lake. Morphologies in each lake are significantly
different from each other (whether by Procrustes or DFA). However,
some lakes have a greater (or more unevenly distributed) field of
morphospace variation within the lake than others. I see this as a
greater spread in the CVA plot. However, it is not helpful for my
further analysis to interpret the output graphs in a strictly
descriptive way (e.g. “Lake A has a bigger field of variation than
Lake B”.
I would like to explore methods/statistical operations that would
permit me to obtain COMPARABLE VALUES that refer to the amount of
within-lake variation of overall body shape per lake (preferably
related to CV1 and CV2). Using these values, I would like to compare
the respective within-lake amount of variation quantitatively with
each other in downstream statistical analyses.
I am just wondering whether I could use exported PC-scores or
CV-scores (x,y coordinates) from MorphoJ for my purpose? Unfortunately
I don´t know how I could extract from these scores the crucial
information about the amount of variation. Or is there some more
suitable statistic I should use?
I would be very glad if somebody could share his advice/experiences with me.
Thanks a lot,
Henrik
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