Measuring the ghost of competition: Insights from density-dependent habitat selection on the co-existence and dynamics of lemmings
Bibliographic record
Abstract
When interspecific competitors resolve their co-existence by habitat segregation, their competition might, like a ghost, be invisible because the species occupy separate habitats. Population fluctuations should often bring the species into competition in jointly occupied habitats where their competition can be measured by habitat isodars (lines or planes of density where the expected fitness of individuals is the same in all occupied habitats). We tested the theory by calculating isodars for two species of lemmings with distinct habitat preferences. When population densities are high, both habitats are occupied by both species. But as densities decline, habitat isodars suggest that the joint dynamics of each species pass through a region where each occupies a separate habitat (the ghost of competition). The competition was asymmetrical. The density of collared lemmings in their preferred habitat was reduced as the density of brown lemmings increased in the same habitat. But collared lemmings had no direct competitive effect on brown lemmings. The interspecific effect from brown lemmings was comparable to – possibly even in excess of – intraspecific competition for habitat. The asymmetric competition for habitat yields spectacular new kinds of isolegs categorizing habitat competition between co-existing species. Although current evidence implicates competition, the patterns are also consistent with apparent competition driven by specialized predators. Regardless of whether lemming habitat use reflects true or apparent competition, the associated densitydependent differences in habitat preference are likely to have major consequences for the nonstable dynamics of lemmings and non-linear lemming isoclines.
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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 | 0.001 | 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 | 0.001 | 0.002 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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 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".