The Contrasting Dynamics of Two Populations of Plantago Lanceolata Classified by Age and Size

(1) The dynamics of two populations of Plantago lanceolata from contrasting habitats are simulated with the use of matrix projection models. The fecundity and survival parameters that together form the matrix are based on demographic fieldwork and evaluated for both size and age categories at the same time. (2) After verification of the model, elasticity analysis is applied to determine the model parameters that are most important in defining the population growth rate. The effect of more complex changes in the life histories on the population growth rate is evaluated by means of simulation. (3) The results are in general agreement with expectations based on field observations: seed production is more important in an unpredictable environment, whereas adult survival is more important in a stable environment. In both populations seedling establishment is the most important phase in the life history, especially in the stable habitat. (4) The formation of side rosettes is not so much a mode of vegetative reproduction as a way to increase the current year's seed production in an unpredictable environment. (5) Timing of germination in spring or in autumn is important, but the effect of delay by means of a seedbank is unexpectedly small. (6) The particular form of this matrix projection model is time-invariant. Because fecundity and survival are rarely constant over time, however, random sequences of bad, normal and good years are generated and incorporated in the model. The impact of this variation over time is evaluated using time-to-extinction as a measure.