Population Dynamics of the Wild Daffodil (Narcissus Pseudonarcissus): III. Implications of a Computer Model of 1000 Years of Population Change

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Abstract
The consequences of varying the rates of mortality, clonal growth and seed reproduction are explored for a population of N. pseudonarcissus over a 1000-yr period, using a simulation model. The range of values assigned to mortality, clonal growth and seed reproduction was based on rates calculated from field data. When field-based rates of reproduction and mortality were kept constant over a long period, or varied under a simulated coppice cycle, extinction of the population or attainment of unacceptably high densities generally resulted. Stabilization at realistic densities was achieved by modifying values for clonal growth to rates intermediate between the extremes recorded in the field. The clump-size frequency distributions of the simulated stable populations closely matched those derived from field data. At normal rates of fertility and mortality there is a continuous turnover of genets. Increasing the rate of clonal growth increased the probability of genet survival and hence the number of genets (the input of new genets being constant). The development of large clonal clumps occurred only at an unrealistically high rate of clonal growth. This is because increasing density reduces the rate of clonal growth. A low-density pattern of individuals and clumps in Narcissus could be produced by certain combinations of mortality and fertility rate; competition from other plant species or unsuitability of the environment was not required to explain gaps between individuals or clumps. Clumps might consist of the members of more than 1 genet, as, over a period of several hundred years, a long-lived genet might become dispersed and parts of it come to lie adjacent to other genets. The strategies of other woodland perennial herbs and the impact of management changes in ancient coppiced woodlands are discussed.