Understanding The Consequences Of Spatial Environmental Variation In A Serpentine Mosaic Landscape

Environmental heterogeneity is ubiquitous in natural systems and in part determines the distributions of plant species both on landscape and local spatial scales. Broadly distributed plant species can respond to environmental heterogeneity via genetic differentiation between populations occurring in distinct patches of environments that are large relative to the spatial scale of dispersal (coarse grained). Fine grained heterogeneity in nutrient, light and water availability occurs on spatial scales that are relevant to seed and pollen dispersal (0.5 to 10m) and is an important determinant of the success of lineages within a population. Dispersing progeny exposed to fine grained heterogeneity can respond via phenotypic plasticity, which enables a single genotype to produce alternative phenotypes in response to its environment. Serpentine soils in Northern California impose harsh and variable abiotic stress on non-adapted plants and have been partially invaded by the invasive annual plant Erodium cicutarium. My dissertation research utilized greenhouse and field experiments to address the following questions in populations of E. cicutarium growing on and off serpentine soils: 1) What is the effect of spatial variation in environmental factors on lifetime fitness on serpentine and non-serpentine soils?, 2) What are the fitness consequences of genetic variation in the expression of phenotypic plasticity in response to continuous multivariate edaphic gradients?, and 3) Do differences in the pattern of spatial edaphic variation within patches of serpentine and non-serpentine soils generate differential selection on the expression of plasticity between soil types? Overall, I demonstrated substantial genetic variation in the expression of phenotypic plasticity by E. cicutarium in response to continuous environmental variation. The fitness consequences of this plasticity were often specific to the trait and environment considered, however the strength of selection on plasticity was significantly stronger on serpentine soils. This differential selection on plasticity was associated with greater small scale edaphic heterogeneity in patches of serpentine soils relative to non-serpentine soils. Additionally, differences in the level of small scale environmental heterogeneity on serpentine and non-serpentine soils generated differential selection on seed dispersal distance in E. cicutarium between soil types.