Hello Geraldina,

Practically this is possible if you adjust the input data accordingly: you may introduce the mean values of δ13C and their standard deviation for the sources table and the absolute values of δ13C for the consumers table, and assume a trophic enrichment factor for each source in a third table.

However, it is not correct to use the SIAR model with only one stable isotope. This means altough the model will bring you an output, the result is meaningless, because there is a restriction in using minimum two stable isotopes.

So I would strongly reccomend you not to use only one stable isotope for your analysis but to add nitrogen stable isotope data for example.

For more information you may check the review by Fry (2013) and the manual for siar, I send you in attachment.

I hope this information help you and good luck with your work!

Best,

Anna-Maria

and the review by Fry (2013)

Anna-Maria thank you very much!

About the restriction you are talking about, do you mean that is conceptual or is relative to the mathematical and statistical model SIAR uses? In what sense the results are meaningless? do you know any bibliographic references where this concept has been written?

hi Geraldina,

you might want to try this "Single isotope example"

http://www.tcd.ie/Zoology/research/research/theoretical/siar/siar_v4.2_single_isotopes.zip

best wishes

KK

Hello again,

the case is that when using only one stable isotope (13C) the model can only distinguish in principle between two sources (if their isotope values are sufficiently apart as well). Indeed I did not explain, my suggestion was that results are meaningless from the 'ecological' point of view, when using one stable isotope for more than three sources for instance (what is usually the case for an ecosystem) and this because the SIAR model can provide still answers on the contributions by there will already be strong overlap. By personal experience, if your sources have carbon isotopes in a short range (close to each other) the contributions of all sources overlap, even if minimizing the SD. Thus, it really depends on your data, and what your question is. Fry et al. are giving some explanation on the above, and also a very interesting paper just came out by J. Middleburg (2013), which also explains very clearly this kind of 'restrictions' with models in food webs.

Best, and good luck,

Anna-Maria

thanks, well understood. could you give me the title of Middleburg et al 2013? I did'nt find it.

Here: http://biogeosciences-discuss.net/10/14923/2013/bgd-10-14923-2013.pdf

Thanks!