Variation in population growth rate in the woodland annual Impatiens pallida ( Balsaminaceae).

All I. pallida seedlings emerged within a few days of each other and a size hierarchy was established within a month, and remained unchanged thereafter. Light and initial seedling density together explained 67% of the variance in mean adult plant size. As a result of differences among populations in the amount of disturbance, survivorship to the time of floral bud production ranged from 39-93% of the initial seedling total. Survivorship during the reproductive period was most affected by plant size and soil moisture. For plants surviving to flowering time, the probability of setting seed, type of seed and number of seeds produced per plant were significantly positively correlated with plant size. Over 82% of all seeds were produced by plants = or >1 m tall. Cleistogamy was the major form of reproduction in 4 out of 5 populations monitored. Net reproductive rate differed greatly among populations, ranging from 1.23-16.27. Population growth rate increased with increasing resource availability and decreasing disturbance during the growing season. -from Authors