I made a semivariogram in R using package gstat, variogram() function. I want to see if there is spatial autocorrelation in the residuals of my model (species abundance as a function of habitat, across sites spaced a few km to 900km apart). My units are in km, and so my interpretation is that the range is just over 100km until spatial autocorrelation is no longer an "issue". I am wondering if someone can explain why the nugget seems so high? Does this mean that even at similar locations, there is still a relatively high degree of difference? Or, does this wavy variogram mean I should adjust my number of lags and lag distance until I get a more typical shape?
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