Coexistence mechanisms and the paradox of the plankton: quantifying selection from noisy data

摘要: Many species of phytoplankton typically co-occur within a single lake, as do many zooplankton (the "paradox the plankton"). Long-term co-occurrence suggests stable coexistence. Coexistence requires that be equally "fit" on average. mechanisms can equalize species' long-term average fitnesses by reducing fitness differences to low levels at all times, and causing relative fluctuate over time, thereby in time-averaged fitness. We use recently developed time series analysis techniques drawn from population genetics estimate strength net selection (time-averaged year) fluctuating (an index variation throughout natural plankton communities. Analysis 99 annual dynamics 49 algal reveals within-year generally is statistically significant but ecologically weak. Rates are -10 times faster laboratory competition experiments than nature, indicating coexistence strong. Most experience selection, fluctuation-dependent may contribute Within-year increases with enrichment, implying among-year such trade-offs between competitive ability resting egg production especially important high enrichment. Fluctuating also enrichment independent temporal variance key abiotic factors, suggesting does not emerge solely conditions, hypothesized Hutchinson. Nor vary among lake-years because more variable conditions comprise stronger perturbations which exhibit frequency-dependent responses, since models this mechanism fail reproduce observed patterns selection. Instead, arise internally generated fluctuations fitness, predicted mechanisms. Our results place novel constraints hypotheses proposed explain paradox plankton.