Hi R-sig-eco. I would like to use the simmr package to estimate percent contributions of C4 v. C3 plants in herbivore diets based on fecal ?13C measurements. I had a few questions, I was hoping someone might be able to help with: 1) Is it correct that observed fecal ?13C values do not need to be adjusted to diet ?13C prior to running simmr if using a correction factor in the model? To me it seems like adjusting and then running the model with a correction factor would be doing it twice and incorrect, but I'd like to be sure. 2) Based on diet?feces fractionations from a feeding study (Table 2 in https://doi.org/10.1139/z03-066), we would like to use a single value of -0.77 (standard deviation: 0.34) for both C3 and C4 sources. For diet?feces fractionation the sign should be input into the model as negative, correct? To implement a single value in simmr, can I simply input the same value for both sources? Thanks for any help! Brian
Brian A. Gill, Ph.D. (He/Him) Postdoctoral Research Associate School of Natural Resources and the Environment University of Arizona, Tucson, Arizona, USA www.BrianGillPhD.com [[alternative HTML version deleted]]