PARENT SESSION
Oral Session #65: Evolutionary Ecology/ Population Genetics. Presiding: G. Gerrish.
Thursday, August 9, 2001. 8:00 AM to 12:00 PM. Hall of Ideas J.
Contemporary pollen movement in California Valley oak, Quercus lobata .
Sork, Victoria1, Davis, Frank2, Smouse, Peter3, 1 2 3
ABSTRACT- Human land use fragments populations and reduces population density in many plant species, thereby contributing to increased reproductive isolation. Valley oak is a widely distributed California species jeopardized by such landscape modification. At Sedgwick Reserve, Santa Barbara Co, we are studying a Valley oak population to estimate the effective number of pollen donors (Nep) and average distance of pollen movement (
). Using our recently developed TWOGENER model, a hybrid of paternity analysis and genetic structure statistics, we analyzed progeny genotypes derived from eight allozyme and two microsatellite loci. We found that (Nep) = 3.43 individuals and that = 60m, based on average adult stem density of d = 1.18 ha 1. We deployed our parameter estimates in spatially-explicit models of the Sedgwick population to ask whether (Nep) has changed due to progressive stand thinning between 1944 and 1993. We discovered that under denser stand conditions in 1944, 99.9% of effective pollen was contributed by the 16 individuals within 113m and the 3 nearest neighbors contributed 50% of the pollen. By 1993, density was reduced to the point that 99.9% of effective pollen was supplied by 13 individuals within 128m; the nearest neighbor (36m from the index tree) accounted for 50% of the effective pollen. Thus, effective pollen movement appears to be restricted and may become further restricted with population decline.
KEY WORDS: pollen-mediated gene movement, pollen pool structure, Valley oak, Quercus lobata