Reproductive asynchrony increases with environmental disturbance

While it is widely recognized that the manner in which organisms adjust the ir timing of reproduction reflects evolutionary strategies aimed at minimiz ing offspring mortality or maximizing reproductive output, the conditions u nder which the evolutionarily stable strategy involves synchronous or async hronous reproduction is a matter of considerable discord. A recent theoreti cal model predicts that whether a population displays reproductive synchron y or asynchrony will depend on the relative scales of intrinsic regulation and environmental disturbance experienced by reproducing individuals. This model predicts that, under conditions of negligible competition and large-s cale environmental perturbation, evolution of a single mixed strategy will result in asynchronous reproduction. We tested this prediction using empiri cal data on large scale climatic fluctuation and the annual timing of repro duction by three species of flowering plants covering 1300-population-years and four degrees of latitude in Norway. In agreement with model prediction s, within populations of all three species reproductive asynchrony increase d with the magnitude of large-scale climatic perturbation, but bore no rela tion to the strength of local density dependence. These results suggest tha t mixed evolutionarily stable strategies can arise from the interplay of co mbinations of agents of selection and the scale at which they operate; henc e it is fruitless to associate synchronous versus asynchronous timing with particular single factors like climate, competition, or predation.