Damien, To your first point (inter-species allometry), you are correct that it does not make sense when there is a significant species:size interaction. In that case, the data have changed one’s question: away from pairwise differences of least squares species means, and towards a question of pairwise differences in allometric slopes. (Note that when the interaction term is not significant, one could use the residuals from a common allometry model as you mentioned, but pairwise comparisons of groups using the shape~size + species and residual randomization will get you there as well, and avoids that additional step).
For environmental groups, the logic is precisely the same. Here one has the model: shape~size + env.gp + size:env.gp. A significant interaction implies that the slopes within each environmental group differ, and so again the data have changed one’s question from that of group differences in means to group differences in slopes. Dean Dr. Dean C. Adams Director of Graduate Education, EEB Program Professor Department of Ecology, Evolution, and Organismal Biology Iowa State University https://www.eeob.iastate.edu/faculty/adams/ phone: 515-294-3834 From: [email protected] <[email protected]> On Behalf Of Damien Esquerre Sent: Monday, July 13, 2020 11:57 PM To: [email protected] Subject: [MORPHMET2] allometric correction Dear morpho community, I have a philosophical question on size correction that should start an interesting discussion. When we are interested in seeing the effects of species or environmental variables for example, on shape, people often first remove allometric variation by computing the residuals of a shape ` size regression. This of course, doesn't make sense if there are heterogeneous slopes and species have different allometric trajectories (i.e. if the species*size term is significant). What do you think would be the most appropriate way to deal with this situation then, if you are interested in environmental effects on shape? Best regards, Damien Esquerré -- You received this message because you are subscribed to the Google Groups "Morphmet" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]<mailto:[email protected]>. To view this discussion on the web visit https://groups.google.com/d/msgid/morphmet2/CAJiv7Cw0S2A%3D-kpEmknt-tUp92Vjy0hkiF%3DVF6C77NsFECP%2BMw%40mail.gmail.com<https://groups.google.com/d/msgid/morphmet2/CAJiv7Cw0S2A%3D-kpEmknt-tUp92Vjy0hkiF%3DVF6C77NsFECP%2BMw%40mail.gmail.com?utm_medium=email&utm_source=footer>. -- You received this message because you are subscribed to the Google Groups "Morphmet" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/morphmet2/CH2PR04MB661735DA5ACF5F5675ACA3DDA2610%40CH2PR04MB6617.namprd04.prod.outlook.com.
