Demography of Floerkea Proserpinacoides, A Forest-Floor Annual: II. Density-Dependent Reproduction

(1) The effect of spatial density of the plants on the seed production of Floerkea proserpinacoides, an autogamous, spring ephemeral forest annual is examined. Field populations were thinned to one of five densities, and repeated counts of flowers, fruits, and seeds were made throughout the growing season. (2) The number of seeds produced by a plant is determined by the number of flowers a plant produces, the proportion of flowers that successfully set seed (`flower survival'), and the number of seeds set per successful fruit. All three decreased as density increased. Mean fecundity was low regardless of density; plants at non-competitive densities produced a mean of only twelve seeds. (3) The rate of flower production was reduced earlier at high density and this was caused by reductions in the number of flower-bearing nodes produced by vegetative buds, rather than a reduction in the number of flowers produced per node. (4) Flowers that were produced early in the season survived better and produced more seeds per fruit than those produced just before the tree canopy closed and light flux decreased. Both flower survival and seed set per fruit were reduced earlier at high density than at low density. (5) Density-dependent population regulation, the effect on fecundity of variable growing season length, the adaptive significance of autogamy, and seed size v. number are discussed.