Age-Specific Survivorship and Reproduction in Phlox drummondii

Abstract

Complete survivorship and fecundity schedules were constructed from observations of a natural population of the winter annual P. drummondii. The data were collected through the complete generation of a cohort of individuals, including the dormant seed phase of the life cycle. Survivorship approached type II during the period of seed dormancy and approached type I for the population after germination. Reproduction was unevenly distributed among individuals, the majority of offspring being produced by a small fraction of the cohort. Estimates of the net reproductive rate RO and the intrinsic rate of increase r are compared with those of other organisms. The rates are lower than those expected of colonizing or r-selected species. Certain annual plants like P. drummondii may have acquired a shortened generation length, but lack the further demographic specialization of many annuals as fugitives or weeds.