LIFE EXPECTANCY IN A TULSA CEMETERY - GROWTH AND POPULATION-STRUCTURE OF THE LICHEN XANTHOPARMELIA-CUMBERLANDIA

The demographics of a population of the foliose lichen Xanthoparmelia cumberlandia growing on gravestones in a Tulsa cemetery are presented. Because of the regular layout of granitic gravestones, the cemetery acted as a mechanism for generating experimental replicates and as a control for habitat variability. The lichen population was multi-modal, based on age classes. Thalli within each age class approximated a normal distribution of size. Age classes were separated by several years. Growth rates of thalli within age classes were independent of size, but growth was dependent on age class. Thallus growth varied among the months, and was correlated with precipitation but uncorrelated with temperature. Mortality rate was greatest in age class III, and lowest in class I (I youngest-III oldest thalli). A population model of the species showed that recruitment has been sporadic, yet highly successful when it did occur. The model depicts growth rates as independent of size within, but not among, the three age classes.