'nlme' package not compiling

Hi,
I'm trying to install from source code the 'nlme' package in 
RStudio. When I try, I get the following error message:

ld: warning: directory not found for option 
'-L/usr/local/lib/gcc/x86_64-apple-darwin13.0.0/4.8.2'
ld: library not found for -lgfortran
clang: error: linker command failed with exit code 1 (use -v to 
see invocation)
make: *** [nlme.so] Error 1
ERROR: compilation failed for package ?nlme?
* removing 
?/Library/Frameworks/R.framework/Versions/3.2/Resources/library/nlme?
* restoring previous 
?/Library/Frameworks/R.framework/Versions/3.2/Resources/library/nlme?
Warning in install.packages :
   installation of package ?nlme? had non-zero exit status

I'm using gfortran 4.8 from Macports and running OS X 10.11.4 
with RStudio Version 0.99.893. I've tried to use the FLIBS 
command in R:

FLIBS="-L/opt/local/lib/gcc48/gcc/x86_64-apple-darwin15/4.8.5/"

so that it knows where the Fortran libraries are at and compile 
again, but it still searchesregardless for the directory:

/usr/local/lib/gcc/x86_64-apple-darwin13.0.0/4.8.2.

which of course doesn't exist. Any suggestions?

Cheers,
Angelo