Looks Can Be Deceiving: Morphological Traits Are Weakly Associated With the Isotopic Niches of Freshwater Fishes
Bibliographic record
Abstract
ABSTRACT Aim Fueled by the emergence of global‐scale databases, fish morphological traits are now routinely used as a proxy for trophic ecology when estimating functional diversity. Yet, a rigorous empirical validation of trophic‐morphology relationships is lacking. This study offers a global test of whether species' morphology is associated with a known indicator of trophic ecology, stable isotope ratios of carbon and nitrogen. Location Worldwide. Time Period 1992–2023. Major Taxa Studied Freshwater fishes (Actinopterygii). Methods Isotope‐morphology relationships were examined using δ 13 C and δ 15 N values from 811 fish communities and ten species‐level morphological traits with direct relevance for foraging behaviour (body length, body shape, and position of the mouth, eyes and fins) for 1282 species. Associations were assessed with Multiple Regression on Distance Matrices and Multivariate Generalised Linear Models (MGLM). Analyses were repeated at the individual level for five fish species. Results Species morphological similarities explained, on average, 10% of the variation in stable isotope values for fish communities, with > 6% of the communities exhibiting statistically significant associations. The MGLM explained 53% of the variation in δ 13 C and 48% in δ 15 N, with approximately 97% and 77% of this variation, respectively, attributed to the site identity (random effect), not the morphological traits. Individual traits contributed minimally (each < 1% variation explained), except for oral gape length (8.3%) and maximum body length (4.7%). Herbivores had significantly weaker isotope‐morphology correlations than omnivores and carnivores for δ 15 N, while no significant differences were observed for δ 13 C. At the individual level, morphology explained 0% to 16% of isotopic variation within populations, averaging 4%. Main Conclusions Weak isotope‐morphology relationships for freshwater fishes may arise from the influence of a host of biological, environmental, or methodological factors, or may truly indicate a fundamental disconnection between morphological traits measured at the species level and the trophic niche of populations that are manifested in food webs. Ecologists should recognise the limitations of assuming morphological traits are ‘functional’ in the sense that they can offer a reasonable proxy of a species' trophic ecology at large scales.
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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 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".