Posterior alpha

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Martha Rosas

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May 3, 2018, 9:13:01 PM5/3/18
to tRophicPosition
Hi!

Can you tell me, what is the interpretation of posterior alpha when plotting the trophic position of different localities (Location along N-S gradient)?

Thank you.


Claudio Quezada R.

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May 4, 2018, 7:26:24 AM5/4/18
to Martha Rosas, tRophicPosition
Dear Martha

The interpretation of posterior alpha is the same, regardless of the number of species that are analyzed or plotted in the same figure: it is the relative proportion of one source vs the other for each species. If one posterior alpha distribution has a mean of 0.8, then the other source, for that species, has a mean of 0.2.

Cheers

Claudio


--
Dr. Claudio Quezada-Romegialli
Profesor Asociado
Departamento de Biología
Facultad de Ciencias Naturales y Exactas
Universidad de Playa Ancha
Teléfono: +56 32 250 0519

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To download tRophicPosition package visit https://github.com/clquezada/tRophicPosition
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Claudio Quezada R.

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May 7, 2018, 2:54:53 PM5/7/18
to tRophicPosition, Martha Rosas
Dear Martha

In the plot attached you have 2 consumers: SEI and SMI (or the same consumer in different locations, the interpretation is the same). Each consumer has different stable isotope Nitrogen values (first panel), but the mean trophic position is similar (around 3.5, second panel), although the 95% credibility interval is quite different for them. Also, the contribution of benthic and pelagic baselines are different for each consumer (third panel, bottom). In the consumer SEI the contribution of the first baseline is rather low, so the other baseline should be high. Please do not confound both consumers, this is an analysis for each consumer. In this plot, only the first baseline is shown.

In case of the consumer or location SMI, the first baseline contributes much more, but the 95% credibility interval goes from 0.25 to 1.00, suggesting there are not many samples (baselines and/or consumer stable isotope values) or they are highly variable.

If you have any questions, please let me know.

Cheers

Claudio


--
Dr. Claudio Quezada-Romegialli
Profesor Asociado
Departamento de Biología
Facultad de Ciencias Naturales y Exactas
Universidad de Playa Ancha
Teléfono: +56 32 250 0519

2018-05-04 12:56 GMT-03:00 Martha Rosas <m.patric...@gmail.com>:
Dear Claudio

Thanks for your reply ... Please, let me understand. In my study, I want to determine the trophic position of a seal in two locations and for each location, I have two baselines (benthic and pelagic), so the "posterior alpha" shown in the plot (attached) reflects the contribution of the two sources in the consumer (if this is the case, why do I have a value close to zero in a locality?, that is, do not have any contribution of baseline on this locality?) or is it a reflection of the contribution of the pelagic baseline on the benthic baseline?.

Forgive me so many questions, but I want to understand the metrics of your model.

Best regards

Martha






El viernes, 4 de mayo de 2018, 5:26:24 (UTC-6), clqu...@harrodlab.net escribió:
Dear Martha

The interpretation of posterior alpha is the same, regardless of the number of species that are analyzed or plotted in the same figure: it is the relative proportion of one source vs the other for each species. If one posterior alpha distribution has a mean of 0.8, then the other source, for that species, has a mean of 0.2.

Cheers

Claudio


--
Dr. Claudio Quezada-Romegialli
Profesor Asociado
Departamento de Biología
Facultad de Ciencias Naturales y Exactas
Universidad de Playa Ancha
Teléfono: +56 32 250 0519

2018-05-03 22:13 GMT-03:00 Martha Rosas <m.patric...@gmail.com>:
Hi!

Can you tell me, what is the interpretation of posterior alpha when plotting the trophic position of different localities (Location along N-S gradient)?

Thank you.


--
To download tRophicPosition package visit https://github.com/clquezada/tRophicPosition
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