Fission and the dynamics of genets and ramets in clonal cnidarian populations

The dynamics of clonal populations involve a range of biological processes controlling "birth" and "death" rates of genets (i.e., clones) and ramets (i.e., the modular subunits of clones). These two levels of organization were examined for open, fissiparous, resource-limited populations using a modified Leslie matrix. Population projections were used to illustrate the method of predicting equilibrium population sizes and clonal structure for hypothetical populations with a range of recruitment, mortality, and fission rates; and to predict these parameters for natural populations of two common, coral reef zoanthids Zoanthus sociatus and Z. solanderi. Fission had the largest impact on population structure when recruitment rates were low and survivorship high. High recruitment rates resulted in the inhibition of density-dependent fission. Low survivorship precluded fission by restricting the number of ramets reaching a size large enough for fission to occur. In projections for zoanthid populations, undisturbed populations reached equilibrium sizes in 2-3 decades, but genet numbers within these populations continued to change over much longer time periods. This result indicates that the clonal structure of natural populations may not be at or near equilibrium and that realistic predictions about this structure will require extensive knowledge of past history.