PARENT SESSION
Oral Session # 92: Biogeography IV: Dispersal.
Presiding: J Choo
Friday, August 8. 8:30 AM to 12:00 PM, SITCC Meeting Room 104.
Estimating pollen dispersal in an invasive grass.
Taylor, Caz*,1, Davis, Heather1, Civille, Janie1, Hastings, Alan1, 1 University of California, Davis, Davis, CA
ABSTRACT- This study investigates the manner in which variation in conspecific density correlates with variation in seed production in a self-incompatible invasive plant. Reproductive rates of isolated Spartina alterniflora at the leading edge of an invasion suffer a more than ten fold reduction in reproductive rate. This wind-pollinated grass, native to the East and Gulf coasts of North America, has invaded mudflats of a large estuary in Willapa Bay, Washington, USA that are historically uninhabited by any other emergent plant. The low reproductive rates suggest that isolated plants are limited in their ability to make viable seed by pollen dispersal distances. This pattern, compounded by the self-incompatibility of S. alterniflora, has the potential to strongly affect the dynamics of this invasion. In order to estimate the shape of the pollen dispersal density function, we measured seed production in fifty plants growing at different degrees of isolation and used remote sensing to map the spatial arrangement of conspecifics in the neighborhood of each plant. We also obtained data describing the wind speed and direction at the study site. We first explored how much of the variation in seed production could be explained by simple neighborhood density measures such as distance to nearest neighbor and area occupied within a known radius. The latter was used to determine the effective neighborhood of pollen dispersal. We then used maximum likelihood to compare the effectiveness in explaining the variation in seed production of several isotropic and non-isotropic spatial models of pollen dispersal.
Key words: Spartina alterniflora, Wind pollination, Pollen Dispersal, Neighborhood density