Density-Dependent Individual and Population-Level Metabolic Rates in a Suite of Single-Celled Eukaryotes

摘要

Population level metabolic rates are by definition the sum of the individual metabolic rates within a population.Several studies have used estimates of individual metabolic rates to scale up metabolic activity of individuals to populationsor whole communities. However, for aquatic single-celled organisms, individual metabolic rate is related to percapitaresource availability, and accounting for this fact is essential for obtaining accurate estimates of population- orcommunity-level metabolism. We frame the problem with a simple model of resource division that predicts per capitametabolic rate should decline with increasing density. We allow the magnitude of density-dependence to be adjusted byintraspecific competition, from perfectly dependent to completely independent of density. Our results demonstrate thatper-capita metabolic rate of single-celled eukaryotes is indeed inversely related to density via the per-capita availability ofresources, and this has a significant effect on population-level metabolic rates. Suppression of individual metabolic rateoccurred up to an order of magnitude, and although this magnitude of suppression has been seen in starved protists, ourresults indicate that a broad continuum of density-dependence governs the resource-dependent variability in metabolicrates for these organisms. The species we used cover a range of resource acquisition modes and phylogenies, suggestingthat density-dependence of metabolic rate may be widespread in aquatic unicells.