AGE-SPECIFIC DEMOGRAPHY INPLANTAGO: VARIATION AMONG COHORTS IN A NATURAL PLANT POPULATION

Abstract

The major starting point to life history analysis is the schedule of repro- duction and mortality; hence, knowledge of age-specific demographic dynamics is needed. The key ingredients to studies on age-specific demography must include large cohorts of individuals of known age, an accurate accounting of all individuals, and an experimental design to facilitate a separation of age-dependent and age-independent dynamics. In this study with Plantago lanceolata, multiple, large cohorts were planted over four successive years, and the individuals were censused monthly for nearly five years. Lon- gitudinal analysis showed seasonal variation in demography that was correlated with max- imum temperature and cumulative precipitation. Cross-sectional analysis of the different cohorts showed variation across cohorts in age-specific demography. The cohort with the lowest juvenile mortality had the highest adult mortality and the lowest fecundity, suggesting that there is an interdependence of demographic patterns across life stages and that the history of mortality within a cohort may be critical to late-age demographic patterns.