integration.Vrel on Size-Corrected Residual Landmarks

[Ricardo Ely]

Dear all, 

I am attempting to evaluate the effects of centroid size on the effect size of eigenvalue variances, but I'm not entirely certain of the correct approach. My intuition, which may be incorrect, says to first perform regression of Procrustes superimposed on centroid size via procD.lm (or procD.lm with phylogenetic vcv a la Natale & Slater 2022), extract the residual landmarks from the output of procD.lm, then perform integration test using the function integration.Vrel using these residual landmarks as the main argument. But would this be the correct approach? It is my understanding that Conaway and Adams 2022 used a different approach to account for allometric effects, by multiplying the Procrustes superimposed landmarks by centroid size. What would be the advantages or disadvantages of using that approach than the one I'm possibly suggesting? 

I searched for other conversations with somewhat related issues, and only found this one on modularity, but not effect size of relative eigenvalue index: https://groups.google.com/g/geomorph-r-package/c/x9nMoVamJEY/m/bh-4JUdNCgAJ

Best, 

Ricardo Ely

[Adams, Dean [EEOB]]

Ricardo,

The 'best' approach depends on what you mean by 'the effect of size' in your analysis. There are size effects and there are allometric effects of size on shape; the latter being the covariation of shape with size. 

Strictly speaking, in Conaway and Adams, we removed the effect of size only, not really allometry. This is accomplished using GPA where size is standardized. Then, we compared the size-free data to size + shape data by adding size back in for an analysis of essentially form. 

The approach in  Natale & Slater 2022 accounted for size in the GPA, but also accounted for the allometric effects of size via regression. Using residuals from that regression accounts for both components, and that is the correct approach if one wishes to remove size-based changes in shape from the data. 

Dean

-- 
Dr. Dean C. Adams
Distinguished Professor
Director, Ecology and Evolutionary Biology Graduate Program
Department of Ecology, Evolution, and Organismal Biology
Iowa State University
www.public.iastate.edu/~dcadams/
phone: 515-294-3834

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From: geomorph-...@googlegroups.com <geomorph-...@googlegroups.com> on behalf of Ricardo Ely <rc...@iu.edu>
Sent: Tuesday, August 26, 2025 6:29 AM
To: geomorph R package <geomorph-...@googlegroups.com>
Subject: [geomorph-r-package] integration.Vrel on Size-Corrected Residual Landmarks

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