Timing of seed dispersal in Daucus carota By: Elizabeth P. Lacey Lacey, E. P. (1982) Timing of seed dispersal in Daucus carota L. (Apiaceae)

This study describes the temporal pattern of seed dispersal in Daucus carota and examines the fate of seeds dispersed at different dates in SE Michigan. Plants varied greatly in both time of onset and rate of dispersal. Onset was directly related to flowering time, a phenotypically plastic character, and tended to occur earlier in newly established populations. Dispersal rate was similar for different-aged populations and for plants flowering at different times. The latter indicates that later-flowering plants dispersed a greater proportion of seeds in winter. Seed germination in outdoor plots declined when dispersal was delayed experimentally. Winter dispersal distances over snow surpassed autumn dispersal distances. However, only in some years did conditions (high winds and snow cover) required for longer distance dispersal occur while many seeds were still viable. Survival and reproduction of autumn-versus spring-germinating offspring varied greatly among years in experimental and natural populations. The fate of seeds dispersed at different times is unpredictable, which may explain the extended dispersal pattern observed in D. carota. Individual variation in dispersal rate is associated with environmental uncertainty in 1) timing of conditions suitable for dispersal over snow and 2) relative success of autumnversus springgerminating offspring. Early onset of dispersal, more common in the youngest populations, improves chances for local population expansion; late onset of dispersal found in older populations improves chances for new site colonization.