EFFECTS OF SEED RELEASE TIMING ON PLANT LIFE-HISTORY AND SEED PRODUCTION IN A POPULATION OF A DESERT ANNUAL, BLEPHARIS-SINDICA (ACANTHACEAE)

Growth, phenology, survivorship, and seed production were observed in a population of a desert annual, Blepharis sindica, with reference to the variation in the timing of seedling emergence. The population cons isted of several cohorts induced by rain-cued seed release within a gr owing season. The fate of 100 individuals of six cohorts was monitored throughout the growing season. Earlier-established cohorts had signif icantly larger plant sizes and higher reproductive outputs than later cohorts. The time and duration of each phenological stage varied among the cohorts, and they were also influenced by plant size. Mortalities at the seedling stage, vegetative stage, and reproductive stage incre ased with the delay of seed release. Seed release was concentrated in the early growing season. Fecundity was highest in the earliest cohort and decreased monotonically in later cohorts. The results suggested t hat even in temporally varying environments, the superiority of early emergent plants was evident. The seed release patterns in temporally f luctuating desert environments are discussed as a compromise between ' diversified bet-hedging' and an optimal timing for maximizing the repr oductive success in a growing season.