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“Carbon and nitrogen stable isotope values of all foods sampled, positioned according to geographic region (A–E). Chains are designated by symbol, stable isotope value is designated by color. The 3 restaurants sampled differ by horizontal
position, whereas the 3 servings differ by vertical position, creating a grid of 9 values for each chain within each city.
Three missing points (C–E) reflect 2 lost substrates from within the entire study (1 serving of chicken and 1 serving of fries).
” source...