1. https://www.R-project.org/
2. Aita M. N. K. Tadokoro N. O. Ogawa F. Hyodo R. Ishii S. L. Smith
3. T. Saino M. J. Kishi S.-I. Saitoh and E. Wada (2011) Linear rela
4. tionship between carbon and nitrogen isotope ratios along simple food
5. chains in marine environments J. Plankton Res. 33(11) 1629-1642