Elith et al. [1] describe a method of measuring the dissimilarity between the values used in model fitting and the values used in making predictions. In the context of species distribution modelling (ecological niche modelling) that prediction is a 'projection'. The method is called 'multivariate environmental similarity surface (MESS) analysis. There is a function in the dismo package to estimate it (as well as a function built into the MAXENT java program).
q1: Does anyone know what units are reported by the dismo::mess function?
The dismo::mess function reports not only a MESS for each predictor (received and reported as a raster), but also reports a layer named 'rmess'. In the help file it is described as " an additional layer with the MESS values".
q2: How are the MESS values calculated?
q3: What is the rmess layer a measure of?
Thanks for your help!
[1] Elith, J., Kearney, M. & Phillips, S. 2010 The art of modelling range-shifting species. Methods in Ecology and Evolution 1, 330-342. (doi:10.1111/j.2041-210X.2010.00036.x).
You can see what dismo does by typing
It calls .messi3, which you can see with