ordiR2step error

Dear list,

I want to run a db-RDA with "capscale" to analyse community data (a distance
matrix created with "betadiv") against pcnm vectors (it will be followed by
db-RDA against environmental variables and eventually variance
partitioning). 
However, when I try to forward select PCNM vectors with the function
"ordiR2step" I get an error

More specifically:

dat.comm<-betadiver(species, method=22, order=FALSE, help=FALSE)
pcnm72<-pcnm(dist(xycart))
dat.pcnm<-as.data.frame(scores(pcnm72))

Following the example of ordiR2step with direction = "forward"

mod0.pcnm<-capscale(dat.comm~1, dat.pcnm)
mod1.pcnm<-capscale(dat.comm~., dat.pcnm)
mod.step.pcnm<-ordiR2step(mod0.pcnm,scope=formula(mod1.pcnm),direction="forward",perm.max=200)

I get the following error

Error in ordiR2step(mod0.pcnm, scope = formula(mod1.pcnm), direction =
"forward",  : 
  the upper scope cannot be fitted (too many terms?)

I would really appreciate it if someone could tell me what this error means
and how to avoid it

Many thanks,
Marika

Marika Galanidi
Post-doctoral Researcher
DEU, Izmir, Turkey




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