Phenotypic plasticity is defined as the ability of an individual organism to alter its morphology and/or physiology in response to changes in environmental conditions. This ability to persist in different environmental conditions reflects the flexibility of that genotype to potential environmental perturbations. Although plasticity is very important to plants because their sessile nature does not permit immediate escape from changing conditions, few studies have examined the role plasticity may play in the conservation of rare and threatened plant populations. This research explores whether or not a change in population size changes the pattern of phenotypic plasticity in a population. The hypothesis is that a decline in population size will result in increased inbreeding and stochastic loss of genetic variation, consequently altering the range of phenotypic plasticity. Growth of genotypes from large and small populations of perennial lupine, an indicator of globally rare oak savanna habitats in the Midwestern United States, will be compared to assess their plastic responses in response to a light gradient. This experiment will answer two specific questions: 1) Do different genotypes within a population differ in their reaction norms to light availability? 2) Do populations differ in their patterns of reaction norms to different levels of light availability? An important task for the conservation of endangered and threatened plant populations is to ensure their long-term persistence. Analysis of plasticity is critical for understanding the capacity of organisms to respond to anthropogenic changes and predicting whether environmental changes will cause genetic shifts within populations.