How to extract posterior data from output_posteriors object?

[naalipalo]

I have similar data to the alligator example with a continuous variable (mine is weight) but my data is significantly different by location (6 sites). The output settings work to produce the graphs I want, but I need to modify the graphs because they change the color of each prey item by location and the titles are wrong etc.... Anyway, I am not certain what data I need to extract and where. Ive been following the code for modifying MixSIAR plots, http://brianstock.github.io/MixSIAR/articles/modify_output.html#set-output-options-to-return-ggplot-objects-1

but it still doesn't have the flexibility I know how to manipulate, so would like to know what to extract from the output_posteriors object created so I can make my own ggplot of the data.