Anthropogenic alterations of lotic food web structure: evidence from the use of nitrogen isotopes
Bibliographic record
Abstract
Understanding the processes that regulate food chain length in nature is a classic theme in ecology. Two factors expected to explain variation in food chain length are resource availability (productivity) and environmental stress. We examined the impact of anthropogenic activities, both a source of stress and productivity, on lotic food webs using two simple food web descriptors based on stable nitrogen isotopes (δ 15 N). We used 1) trophic position of small fish and 2) slopes of δ 15 N‐size class relationships in the invertebrate community as variables related to food chain length. Trophic positions and δ 15 N‐size slopes changed significantly across the 23 study sites selected to vary in productivity and impact from industrial activities (trophic position=0.4 to 1.9; slopes=−1 to +2.8). Fish trophic position was not affected by productivity (chlorophyll a) or environmental stress (number of factories on the watershed) and was not modulated by the proportion of predatory invertebrates in the food web leading to fish. This lack of relationship suggests that variation in trophic position is likely influenced by fish feeding behaviour and is therefore not a good integrator of changes in food chain length induced by anthropogenic activities. δ 15 N‐size slopes significantly increased with productivity and decreased with stress, suggesting that trophic organization by size within invertebrate communities is affected by these factors. These slopes also tended to be greater when the proportion of predators in the community increased in larger size classes. These results suggest that when productivity is high and stress is low, proportions of higher δ 15 N‐value predators in lotic food webs tend to increase, contributing to the lengthening of food chains. They also suggest that δ 15 N‐size relationships of invertebrate communities may be used as indicators of food web structure alteration by human activities.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| 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 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.004 | 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 teacher head, 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".