• colonization;
  • genetic drift;
  • migration;
  • seed bank;
  • seed dispersal


  • Plants may escape unfavorable environments by dispersing to new sites, or by remaining in an ungerminated state at a given site until environmental conditions become favorable. There is limited evidence regarding the occurrence, interplay and relative importance of dispersal processes in time and space in plant populations.
  • Thirty-six natural populations of the annual ruderal species Arabidopsis thaliana were monitored over five consecutive years, sampling both seed bank and above-ground cohorts.
  • We show that immigration rates are considerably higher than previously inferred, averaging 1.7% per population yr–1. On the other hand, almost one-third of the individuals in a given above-ground cohort result from seeds shed 2 or 3 yr back in time in 10 of the studied populations. Populations that disappeared one year were recolonized by regeneration from the seed bank the subsequent year.
  • Thus, dispersal in both time and space is an important contributor to the structuring of genetic variability in natural populations of A. thaliana, where a high dispersal rate in time may partly counteract the homogenizing effects of spatial seed and pollen dispersal.