[R-sig-eco] Detecting spatial gradient whilst accounting for spatial autocorrelation
Peter Francis
peterfrancis at me.com
Wed Apr 20 16:25:00 CEST 2011
Dear List
I have a data set which shows high levels of spatial autocorrelation, the sampled plant communities are on a global scale and i am looking for correlates of different diversity measures (PD,FD).
I have controlled for the spatial autocorrelation using a GLS model where the latitude and longitude of each ecoregion was included as a smooth factor in all-statistical models using the corExp function.
i.e
exponential <-corExp(form = ~ Longitude + Latitude)
PD_global <- gls(PD~Elevation+Temperature+Species_Richness, correlation = exponential)
Now i want to ask the question; how do these diversity measure vary with latitude and longitude i.e is their a spatial gradient to PD or FD, i don't think i can put in longitude or latitude as a predictor if i am using it as a random variable through the corExp function
i.e
PD_global <- gls(PD~Elevation+Temperature+Species_Richness, ALtitude + Longitude, correlation = exponential)
But i imagine it is something that is often asked?
Any help would be greatly appreciated.
Thanks in advance
Peter
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