Dear Dr. Braaker,
I use the function eisera in the package Adehabitat to perform a habitat selection analysis. Is there a way to get the variance explained by the first and by the second habitat selection axes from the output? Or a simple way of calculating them?
I do not know why you need to calculate the variance explained by the first two axes of the eisera. This method find axes that maximise the selection ratios (see Calenge, C. and Dufour, A.B. (2006) Eigenanalysis of selection ratios from animal radio-tracking data. Ecology. 87, 2349-2355), by partitionning the chi-square statistic defined by White and Garrott (1990). Therefore, the choice of the number of axes should be done with respect to the proportion of this chi-square statistic explained by each axis (which can be calculated easily by ana$eig/sum(ana$eig), where ana is the object returned by the function eisera). However, if you want to calculate the variance of each axis, just type var(ana$li[,1]) for the variance of the first axis, or apply(ana$li, 2, var) for the variance on all axes.
Best regards, Clément Calenge.
Thanks for any hints Sonja
-- Clément CALENGE Cellule d'appui à l'analyse de données Direction des Etudes et de la Recherche Office national de la chasse et de la faune sauvage Saint Benoist - 78610 Auffargis tel. (33) 01.30.46.54.14 _______________________________________________ AniMov mailing list AniMov@faunalia.it http://lists.faunalia.it/cgi-bin/mailman/listinfo/animov
