Dear R-sig-phylo,
I am fairly novice to the field of phylogenetic comparative methods and I was
hoping to gain some advice regarding the study of ordinal (pseudo-continuous)
morphological data.
I am currently studying morphological convergence associated with habitat
transitions in Australian lizards. To some extent my data is very similar to
Mahler et al. (2010, 2013), with several measurements of continuous traits such
as SVL, limb length, head length etc. However in addition to metric data, I
also have estimates of feet morphology such as the number of toe lamellae.
Now my question is whether it is statistically appropriate to analyse meristic
data, such as lamellae number, in exactly the same way as the metric data? In
particular in reference to for example running a Phylo PCA with size corrected
residuals, phylo-anova (to test for correlation between habitat and trait) and
running SURFACE to test for convergence?
Part of the reason why I would like your advice, is because the variation in
counts is much less than for example in Mahler's study; in my case the
differences in lamellae number ranges from 12 to 17, across 26 species. Ingram
(2014) mentioned: "We note that one trait (gill raker number) is meristic
rather than metric but that it is variable enough that species means were
effectively continuous and approximately normally distributed...". I would like
to ask if someone would have a suggestion how to assess whether the meristic
traits can be considered as 'variable enough', to treat it as
pseudo-continuous? Is this for example commonly done by traditional tests for
normality? And if it's not variable enough, could you recommend an alternative
approach?
Many thanks, your help is much appreciated!
Best,
Moos
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