Is plant community richness regulated over time? Contrasting results from experiments and long-term observations
Bibliographic record
Abstract
There is considerable debate among ecologists as to whether or not communities are saturated. In saturated communities, species richness should remain relatively constant over time, despite compositional turnover, because richness is negatively correlated with colonization and positively correlated with local extinction. Few studies have tested for saturation using temporal observational data as well as diversity-perturbation experiments. We analyzed 10 years of data for plant species richness at 71 sites on contrasting serpentine and non-serpentine soils within Californian (USA) grasslands. We also manipulated local richness and measured its effects on immigration and extinction. Consistent with saturation, we observed that richness was positively correlated with extinction rates and negatively correlated with colonization rates, and randomization tests confirmed that diversity fluctuated less than expected by chance. However, experimental species additions and removals did not affect extinction or colonization, suggesting that richness is not regulated by local species interactions. Instead, we propose three reasons why richness may fluctuate within narrow limits causing the appearance of saturation in temporal observational data sets: negatively autocorrelated patterns of biotic response to yearly conditions, differential affinities of particular species for local conditions, or stochastic abundance-dependent colonization and extinction rates. We illustrate the latter using a metacommunity model.
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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) | 0.001 | 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 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".