Introduction:According to the empirical regularity called Taylor’s law,the variance of population density in samples of populations is a power of the mean population density.The exponent is often between 1 and 2.Our ...Introduction:According to the empirical regularity called Taylor’s law,the variance of population density in samples of populations is a power of the mean population density.The exponent is often between 1 and 2.Our experiments investigated how genetics,evolution,and environment shape Taylor’s law.Methods:Genetically different strains(wild type and hypermutator)of the bacterium Pseudomonas fluorescens evolved and were assayed under different environmental conditions(with and without antibiotic rifampicin and bacteriophage SBW252,separately and in combination).Results:Experimental treatments altered the exponent b,but not the power law form,of the relation between variance and mean population density.Bacterial populations treated only with rifampicin had a narrow range of mean population densities and exponent b=5.43.Populations exposed to rifampicin plus phage had b=1.51.In ancestral,control,and phage-exposed populations,mean abundance varied widely and b was not significantly different from 2.Evolutionary factors(mutation rate,selection)and ecological factors(abiotic,biotic)jointly influenced b.Conclusions:Taylor’s power law relationship accurately and robustly described variance as a function of mean population density,with overall exponent b=1.89.These and other experiments with different factors acting on bacterial population size support the relevance of models that predict‘universal’patterns of fluctuation scaling.展开更多
基金The collection of the data analyzed here was funded by grants from the French Agence National de la Recherche(ANR)‘CoMute’(ANR-06-BLAN-0164)and‘EvolStress’(ANR-09-BLAN-099-01)MEH and OK were supported by grants‘EvolStress’(ANR-09-BLAN-099-01)and‘EvoRange’(ANR-09-PEXT-011)JEC was supported in part by grant EF-1038337 from the U.S.National Science Foundation,a grant from the region of Languedoc-Roussillon through the University of Montpellier 2,the assistance of Priscilla K.Rogerson,and the hospitality of Michael E.Hochberg and family during this work.Two referees provided helpful criticisms and suggestions.This is publication ISE-M 2012-032.
文摘Introduction:According to the empirical regularity called Taylor’s law,the variance of population density in samples of populations is a power of the mean population density.The exponent is often between 1 and 2.Our experiments investigated how genetics,evolution,and environment shape Taylor’s law.Methods:Genetically different strains(wild type and hypermutator)of the bacterium Pseudomonas fluorescens evolved and were assayed under different environmental conditions(with and without antibiotic rifampicin and bacteriophage SBW252,separately and in combination).Results:Experimental treatments altered the exponent b,but not the power law form,of the relation between variance and mean population density.Bacterial populations treated only with rifampicin had a narrow range of mean population densities and exponent b=5.43.Populations exposed to rifampicin plus phage had b=1.51.In ancestral,control,and phage-exposed populations,mean abundance varied widely and b was not significantly different from 2.Evolutionary factors(mutation rate,selection)and ecological factors(abiotic,biotic)jointly influenced b.Conclusions:Taylor’s power law relationship accurately and robustly described variance as a function of mean population density,with overall exponent b=1.89.These and other experiments with different factors acting on bacterial population size support the relevance of models that predict‘universal’patterns of fluctuation scaling.
