Demographic variation in Alliaria petiolata (Brassicaceae) in four contrasting habitats

The expansion of Alliaria petiolata into a broad range of habitats in New Jersey was examined by comparing demographic and reproductive characteristics in four habitats that differed in availability of moisture and light. Plants behaved as strict biennials in all sites in all years. Survivorship, seed weight, and seed germination were lower in the drier habitats. The timing of flowering was later (1-2 weeks) in the drier habitats, although it did not appear to affect fruit maturation (as estimated by fruit abortion) which occurred during the drier months in all sites. Fecundity as measured by seeds/fruit and fruit production significantly differed among the populations although seeds/plant did not differ. Fruit abortion, which differed among the populations and among years, may be most influenced by environmental fluctuations rather than any characteristics intrinsic to the sites. The allocation of resources (biomass) to reproduction was greatest in the most disturbed site. A common garden experiment using seedlings from the two most contrasting sites suggested that variation in most traits (flowering phenology and resource allocation) was primarily a response to the environment. However, survivorship was more affected by seedling origin. This research suggests that A. petiolata responds to the broad range of habitats primarily by phenotypic plasticity. While A. petiolata had lower survivorship in the drier habitats; its phenotypic variation in demographic and reproductive characteristics may have allowed successful range expansion.