Individual variation in nursing duration and resource use among narwhals (Monodon monoceros) from eastern Canadian Arctic using stable isotopes (d13C and d15N) of dentine from embedded teeth
Bibliographic record
Abstract
Individual variation in nursing duration and resource use can have cumulative effects on population growth and species resilience in response to resource changes. There have been climate-induced shifts in prey resources in the Arctic since the 1980s; however, knowledge regarding narwhal nursing and dietary variation at the individual level remain understudied. Stable isotope analysis (SIA) of sequential dentine samples can provide a longitudinal record of isotopic (13C and 15N) values that help infer age at which nursing completes, and assess diet. This study used SIA of dentine from narwhal embedded teeth to investigate individual nursing duration and dietary variation within a population over two time periods (pre- and post- 1982/1983). Embedded teeth were collected near Pond Inlet, Nunavut, from both sexes in 1982/1983 (n = 13) and 2015/2017 (n = 14). Ontogenetic 13C and 15N profiles were constructed for individual narwhals. Nursing duration was inferred based on postnatal 15N decline over age 1–10, and I found nursing in narwhals lasted for two to six years but most individuals started feeding primarily on solid food after 12 months. Nursing duration did not differ between sexes nor between the two time periods. To analyze variation in narwhal diet after nursing being completed, I evaluated 13C and 15N values and isotopic niche breadth for individuals within each period and at the population level between the two time periods. Narwhals varied significantly in their isotope values and isotopic niche, suggesting individuals may differ in resource use (prey size, proportion, and feeding locations), as well as the range and consistency of resource use over one’s lifetime. Across time periods, narwhals showed a slight niche expansion, likely reflecting a dietary shift to incorporate alternative subarctic prey that have increased in availability in the Arctic over the past 30 years. This study provides new information on narwhal life history, highlighting the variability in narwhal nursing duration and individual-level resource use, which can be applied to future assessments that consider narwhal foraging flexibility in response to climate-induced resource shifts.
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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 | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.002 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
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".