Isotope analysis
Nitrogen-15

Nitrogen isotopes indicate the trophic level position of organisms (reflective of the time the tissue samples were taken). There is a larger enrichment component with δ 15 N because its retention is higher than that of 14 N. This can be seen by analyzing the waste of organisms. Cattle urine has shown that there is a depletion of 15 N relative to the diet. As organisms eat each other, the 15 N isotopes are transferred to the predators. Thus, organisms higher in the trophic pyramid have accumulated higher levels of 15 N (and higher δ 15 N values) relative to their prey and others before them in the food web. Numerous studies on marine ecosystems have shown that on average there is a 3.2‰ enrichment of 15 N vs. diet between different trophic level species in ecosystems. In the Baltic sea, Hansson et al. (1997) found that when analyzing a variety of creatures (such as particulate organic matter (phytoplankton), zooplankton, mysids, sprat, smelt and herring,) there was an apparent fractionation of 2.4‰ between consumers and their apparent prey.
keywords:existence