Interlacing roles of bottom‐up, top‐down, endogenous, and anthropogenic factors in population oscillations
Bibliographic record
Abstract
Abstract The relative importance of bottom‐up, top‐down, and endogenous factors in population oscillations has been vigorously debated, yet few longer‐term studies of population dynamics have considered their potential nonadditive interactions. This study tests the hypothesis that oscillations can arise from the combined effects of bottom‐up, top‐down, and endogenous factors, with some of these factors being sensitive to anthropogenic modifications of habitats. Populations of Neodiprion abietis , a univoltine sawfly whose oscillations have strong first‐ and second‐order components, were monitored over six to eight generations in a natural and an adjacent managed (precommercially thinned) balsam fir ( Abies balsamea ) stand at each of three sites in Newfoundland, Canada. Endogenous and exogenous factors affecting N. abietis were evaluated to identify the factors contributing to first‐ and second‐order density dependence and uncover any differences in dynamics attributable to forest management. In both natural and managed stands, N. abietis populations remained at high densities for 2–4 yr before collapsing. At the beginning of outbreaks, immigration, high fecundity, female‐biased sex ratios, and high survival in later larval instars and during the cocoon stage allowed N. abietis populations to increase rapidly. After this increasing phase, top‐down (mortality by the baculovirus Neodiprion abietis nucleopolyhedrovirus [ Neab NPV ] and, under some circumstances, parasitism by Mesopolobus verditer ) and bottom‐up (host‐plant) exogenous factors combined with endogenous factors associated with recruitment to initiate the localized collapse of N. abietis populations. Because first‐order density dependence was attributable to Neab NPV (and sometimes M. verditer ) and second‐order density dependence was attributable to host‐plant effects and endogenous factors associated with recruitment, these factors are inferred to cause the periodic behavior of this species. Host‐plant effects, but not top‐down mortality factors, were more pronounced in natural than thinned stands, suggesting that recent increases in N. abietis outbreak severity and range are best explained by a management‐induced reduction of host‐plant effects. By considering nonadditive interactions between trophic forces, this study reveals the intricate relationships between the factors responsible for population oscillations that would otherwise remain hidden.
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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) | 0.005 | 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".