I am using PAST software to apply on morphometrics of fish. Can anyone tell me can I remove size effect using PAST as there is option present "remove size from distances" with ''allometric vs standard" which as based on Elliott, 1995 formula. But the confusion is that as Elliott formula is based on standard length, while PAST doesn't demand to feed standard length given in data and directly modify the values.
If someone is using PAST, kindly guide me in this regard. Thank you in anticipation.
Dear Muhammad:
As you say, the filter "Remove size from distances", option "Allometric vs. standard", is useful to remove the size effect. This tool standarize the sizes of your specimens to an ideal size (the mean size of your individuals), taking an arbitrary variable as a reference.
The total length is commonly the variable most used to standarize, because intiutively it represents the "size" of the specimen. But if you want, you can use any other variable as reference. For example, you could have an organism in which the total lenght doesn't represent the "size" well, but maybe the maximum width does it better. In this case, you could use this last variable as reference, and you can perform the transformation according to it.
Therefore, the tool in PAST is designed in this way:
The first column (first variable) will be taken automatically as the reference measure, and you can see that after the transformation this column will have the same value for all the specimens. This is the mean value of all the measurements, for that variable.
Therefore, if you want to transform using the total length, this variable must be the first in your matrix.
As a note, this transformation was proposed first by Lombarte & Lleonart (1993), and then was taken by Elliot et al. (1995).
Later, Lleonart et al. (2000) publish a paper where they bring a detailed explanation of how this transformation works, with examples. I recommend to you the lecture of this last paper.
Here you have the references:
Lleonart, J.; Salat, J. and G. J. Torres. 2000. Removing Allometric Effects of Body Size in Morphological Analisys. Journal of Theoretical Biology, 205: 85-93. DOI: https://doi.org/10.1006/jtbi.2000.2043
Lombarte, A. & J. Lleonart. 1993. Otolith size changes related with body growth, habitat depth and temperature. Environmental Biology of Fishes, 37: 297-306. DOI: https://doi.org/10.1007/BF00004637
I hope this answer could help you.
Best regards from Uruguay.
Dear Pablo Toriño
Thank you so much such detailed instruction. I solved it by following your instructions. Your help meant a lot for me
Dear Muhammad:
Your'e welcome. Good luck in your research!
Best regards
Pablo.
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