Thursday, August 6, 2009: 1:50 PM
Picuris, Albuquerque Convention Center
Background/Question/Methods Oaks are a dominant component of many North American forests, yet in many areas oak seedling production is declining. Oaks are generally thought to be highly dispersal limited, which could make reaching scarce recruitment sites more difficult. In addition, short-range dispersal may limit oaks’ ability to respond to climate change via migration or local adaptation. However, dispersal kernels in oaks are not well captured by traditional seed-trap-based methods. In this study, we apply a Bayesian parentage model developed for monoecious plants to two populations of red oak (Q. rubra) in North Carolina, one in the Piedmont (12 ha), one in the Appalachians (7.5 ha). The model incorporates genetic data, as well as location and fecundity data. Both censused plots are located in diverse secondary hardwood forests where oaks are abundant in the canopy; however, they differ in a number of other ecological factors. We ask whether the scale of effective seed and pollen movement differs between these populations and, if so, this difference can be explained by site history and plant-animal interactions.
Results/Conclusions Allelic diversity was high at both sites, averaging >20 alleles per locus, but patterns of recruitment and gene flow differed markedly between the sites. Parentage assignment in the Piedmont was surprisingly low, with more than a third of seedlings lacking a possible in-plot parent. Among consistent matches, the average parent-offspring distance was >150 m. Although at the Appalachian site a lower percentage of adult trees had been genotyped a greater proportion of seedlings were matched to in-plot adults, and the average dispersal distance for consistent matches was <50 m. This difference is most likely due to biotic interactions; disperser activity is higher at the Piedmont site, but so is herbivory, which, when density dependent, can lead to increased apparent dispersal distances. Patterns of spatial genetic structure are consistent with the site history - colonization from local source trees in the Appalachians, vs. multiple distant sources in the Piedmont. Based on effective dispersal distances, the Piedmont population would yield higher potential migration rates. Results suggest that some oak populations are less dispersal limited than has been thought, suggesting that regeneration and population expansion are best promoted by favorable disturbance frequencies and reduced herbivory.
Results/Conclusions Allelic diversity was high at both sites, averaging >20 alleles per locus, but patterns of recruitment and gene flow differed markedly between the sites. Parentage assignment in the Piedmont was surprisingly low, with more than a third of seedlings lacking a possible in-plot parent. Among consistent matches, the average parent-offspring distance was >150 m. Although at the Appalachian site a lower percentage of adult trees had been genotyped a greater proportion of seedlings were matched to in-plot adults, and the average dispersal distance for consistent matches was <50 m. This difference is most likely due to biotic interactions; disperser activity is higher at the Piedmont site, but so is herbivory, which, when density dependent, can lead to increased apparent dispersal distances. Patterns of spatial genetic structure are consistent with the site history - colonization from local source trees in the Appalachians, vs. multiple distant sources in the Piedmont. Based on effective dispersal distances, the Piedmont population would yield higher potential migration rates. Results suggest that some oak populations are less dispersal limited than has been thought, suggesting that regeneration and population expansion are best promoted by favorable disturbance frequencies and reduced herbivory.
