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Abstract

A common measure of generation time is the average distance between two recruitment eventsalong a genetic lineage. In populations with stage structure that live in a constant environment,this generation time can be computed from the elasticities of stable population growth to fecun-dities and it is equivalent to another common measure of generation time: the average parentalage of reproductive-value weighted offspring. Here, we show three things. First, when the envi-ronment fluctuates, the average distance between two recruitment events along a genetic lineageis computed from the elasticities of the stochastic growth rate to fecundities. Second, underenvironmental stochasticity, this measure of generation time remains equivalent to the averageparental age of reproductive-value weighted offspring. Third, the generation time of a popula-tion in a fluctuating environment may deviate from the generation time the population wouldhave in the average environment.