Here are a couple of good ones

Cheers,

Rick

Thanks Richard - I have those, but will put a star on them so I am sure to re-read them.

Hello Marshall, 

Have you checked this one?

Good luck!

You may know or have read them already, but Stéphane Caut's recent-ish papers on fractionation or discrimination factors and diet quality might be of interest (2009 Journal of Applied Ecology; 2008 Functional Ecology; 2010 Journal of Applied Ecology; etc.)

Thanks Eric - these are excellent!!

Please be somewhat careful in using Caut's approach. There are problems with autocorrelation and other statistical issues. Moreover, experimental data tend to be biased due to incomplete isotopic equilibrium (cf. Fig. 3 in McCutchan et al. 2003).

These problems were noted and discussed in several publications, see Auerswald et al. (2010), Perga & Grey (2010), and Sabat et al. (2013).

Unfortunately, the paper by Hussey et al. 2013 (Ecology Letters) has the same drawbacks. One can re-analyze experimental studies used in their dataset to see that the dependence of D15N on d15N rests mostly on short-time laboratory studies, where a "new diet" was enriched in 15N relative to the "old diet".