Do δ<sup>15</sup>N and δ<sup>13</sup>C values of feces reflect the isotopic composition of diets in small mammals?
Bibliographic record
Abstract
The stable isotope composition of carbon and nitrogen in feces can be a useful tool for reconstructing diet. To examine whether the isotopic composition of feces reflect those of diet, we determined the fractionation of 15 N and 13 C along the digestive tracts of several species of small mammals. There were significant differences in the δ 15 N values of digesta in different compartments of the gastrointestinal (GI) tract, with consistent enrichment of 15 N in the stomach, intestine, and cecum, and the depletion of 15 N in the colon (i.e., feces). Although feces had lower δ 15 N values than digesta in the cecum, feces of small mammals were significantly more enriched in 15 N (by ~2.5‰) than diet. The mechanisms causing this enrichment in the GI tract may arise from the operation of different biochemical pathways within the different GI compartments. The stable carbon isotope composition of digesta in small mammals were similar along the GI tract, but the δ 13 C values of digesta and feces were significantly lower than reported previously for large ungulates (–3.5‰ vs. –0.5‰). The δ 15 N and δ 13 C values of feces did not directly reflect the isotopic compositions of these mammals’ diet. Our data offer evidence for variations in isotopic discrimination effects. This variation can probably be ascribed to metabolism of different body sizes of mammals and the complexities linked with digestive physiology of herbivores.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".