The timing of life-history events in a changing climate

Although empirical and theoretical studies suggest that climate influences the timing of life-history events in animals and plants, correlations betwe en climate and the timing of events such as egg-laying, migration or flower ing do not reveal the mechanisms by which natural selection operates on lif e-history events. We present a general autoregressive model of the timing o f life-history events in relation to variation in global climate that, like autoregressive models of population dynamics, allows for a more mechanisti c understanding of the roles of climate, resources and competition. We appl ied the model to data on 50 years of annual dates of first flowering by thr ee species of plants in 26 populations covering 4 degrees of latitude in No rway. In agreement with earlier studies, plants in most populations and all three species bloomed earlier following warmer winters. Moreover, our mode l revealed that earlier blooming reflected increasing influences of resourc es and density-dependent population limitation under climatic warming. The insights available from the application of this model to phenological data in other taxa will contribute to our understanding of the roles of endogeno us versus exogenous processes in the evolution of the timing of life-histor y events in a changing climate.