DEMOGRAPHIC VARIATION IN ALLIARIA-PETIOLATA (BRASSICACEAE) IN 4 CONTRASTING HABITATS

The expansion of Alliaria petiolata into a broad range of habitats in New Jersey was examined by comparing demographic and reproductive char acteristics in four habitats that differed in availability of moisture and light. Plants behaved as strict biennials in all sites in all yea rs. Survivorship, seed weight, and seed germination were lower in the drier habitats. The timing of flowering was later (1-2 weeks) in the d rier 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 producti on significantly differed among the populations although seeds/plant d id not differ. Fruit abortion, which differed among the populations an d among years, may be most influenced by environmental fluctuations ra ther than any characteristics intrinsic to the sites. The allocation o f resources (biomass) to reproduction was greatest in the most disturb ed site. A common garden experiment using seedlings from the two most contrasting sites suggested that variation in most traits (flowering p henology and resource allocation) was primarily a response to the envi ronment. However, survivorship was more affected by seedling origin. T his research suggests that A. petiolata responds to the broad range of habitats primarily by phenotypic plasticity. While A. petiolata had l ower survivorship in the drier habitats; its phenotypic variation in d emographic and reproductive characteristics may have allowed successfu l range expansion.