Browsing by Author "Potter, Kevin Mark"

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Evolutionary History and Genetic Conservation of Fraser Fir (Abies fraseri [Pursh] Poir.)
(2006-08-11) Potter, Kevin Mark; Dr. John Frampton, Committee Chair; Dr. George R. Hess, Committee Member; Dr. Qiu-yun (Jenny) Xiang , Committee Member; Dr. Michael D. Purugganan, Committee Member
Fraser fir (Abies fraseri [Pursh] Poir.) is a glacial relict species endemic to high peaks in the Southern Appalachians. A conifer with considerable ecological and economic importance, it has been devastated by the infestation of the balsam woolly adelgid (Adelges piceae Ratz.), an exotic insect from Europe. Fraser fir is a potentially informative and interesting model species for the study of forest tree population genetics and ecology because of (1) the fragmented nature of its populations, (2) the threat to the continued existence of its natural stands from the adelgid and from global climate change, and (3) its unclear relationship with other North American Abies species. These characteristics are also compelling reasons for conserving its genetic composition. I developed a series of stage-structured population matrix models for Fraser fir to simulate genetic dynamics in a long-lived forest tree species with overlapping generations. The results suggest that Fraser fir populations are large enough and its life cycle is long enough to avoid significant genetic drift, absent repeated adelgid infestations. The model results indicate that other forces, including natural selection and inter-population pollen exchange, are more likely to have influenced the genetic structure of the species. I used microsatellite molecular markers to assess the genetic structure and genetic diversity of Fraser fir populations. This analysis found only slight differentiation among populations, but greater inbreeding and less observed heterozygosity than in other conifers. No genetic diversity measure was correlated with population size, suggesting that smaller populations did not suffer more extensively from detrimental genetic effects following post-Pleistocene fragmentation. While some gene flow may occur between populations in close proximity, the genetic architecture of the species is more likely a function of its post-glacial migratory history. Unexpectedly, some of the smallest Fraser fir populations were the most genetically diverse by some measures, and the largest and least isolated populations were among the least diverse. Using the same microsatellite loci, I detected a relatively small amount of differentiation among Fraser fir, balsam fir (Abies balsamea [L.] Mill.), and intermediate fir (A. balsamea var. phanerolepis Fern.), suggesting that these taxa should be treated as varieties of the same species. Balsam fir appears to consist of three demes, suggesting the possibility of one large central fir refuge during the Pleistocene, with smaller refugia to the east and west. Fraser fir, with highly exserted and reflexed cone bracts, may represent an adaptive extreme of balsam fir that, during post-Pleistocene isolation, lost genetic contact with relatives lacking exserted bracts. The results also indicated the probable introgression of subalpine fir (A. lasiocarpa [Hook.] Nutt.) genes into balsam fir. I conclude that in situ conservation of Fraser fir's genetic composition is currently adequate, but may be insufficient in the face of global climate change and repeated adelgid infestations. A concerted ex situ strategy is needed to thoroughly conserve the genetic diversity of the species. I developed such a strategy for Fraser fir with two objectives: (1) to preserve its natural population genetic diversity in case Fraser fir populations are extirpated or degraded, and (2) to conserve and make available Fraser fir genetic resources for the breeding of an economically important tree species. The ex situ gene conservation strategy has four central components: (1) a seed bank representing all the Fraser fir populations, (2) existing elements of tree breeding efforts, (3) conservation plantings, and (4) an archive of Fraser fir DNA.
Landscape characteristics and North Carolina stream life: A multiple-scale ecological risk assessment of nonpoint source pollution
(2002-10-16) Potter, Kevin Mark; Dr. George R. Hess, Committee Member; Dr. Frederick W. Cubbage, Committee Chair; Dr. Gary B. Blank, Committee Member
Nonpoint sources of pollution may be responsible for as much as 50 percent of current water quality degradation in the United States, and as much as 70 percent in the Southeast. In this study, I used an ecological risk assessment methodology, at the watershed scale and riparian scales (zones 300, 100, and 50 feet on either side of streams), to analyze and quantify the impact of nonpoint pollution on the ecological integrity and water quality of North Carolina streams. Specifically, I determined how land-use patterns relate to aquatic ecological integrity, including the extent to which one of the most widely promoted best management practices (BMPs) – the preservation of riparian vegetated buffers – correlates with better ecological integrity. The central goal of this project was the creation of a set of empirical models that describe the vulnerability of North Carolina aquatic ecological integrity – as measured by benthic macroinvertebrate community structure - to changes in the landscape-scale sources of nonpoint pollution. The models, the result of multiple regression analysis of Geographic Information System (GIS)-derived data, take into account watershed eight land form characteristics, and three land cover types derived from 1992 Multi-Resolution Land Characterization (MRLC) Consortium raster data: forest, urban, and agriculture. The land form characteristics considered in this analysis are topographic complexity, mean elevation, watershed slope/relief ratio, watershed area, watershed shape, rainfall, soil clay content, and ecoregion. The regression equation models created by this process can be used by managers and policymakers to weigh the risks of management and policy decisions for a given watershed or set of watersheds, including whether vegetated riparian buffers are ecologically effective and economically efficient in achieving water quality standards. The coefficient of multiple determination (R²) for each equation indicates the proportion of variability in the invertebrate tolerance indices attributable to the landscape variables included in the model. The unstandardized regression coefficients for each landscape variable represent that variable's weight and direction in the vulnerability index equation. The standardized (beta weight) regression coefficients indicate the relative importance of the landscape characteristic relative to the other landscape variables in the model equation. The results of this study indicate that (1) landscape characteristics at the watershed scale predict variability in benthic macroinvertebrate community structure better than characteristics at the riparian scale; (2) land cover variables are of secondary importance to certain land form features, but are still significant predictors of macroinvertebrate community structure; (3) developed land use is the most important land cover variable at the watershed scale, while forested land cover is the most important at the riparian scale; (4) wider riparian buffer zones yield only minor differences in invertebrate community structure; and (5) more research is needed on how these interactions vary by the size of a watershed and the ecoregion in which it is located. Based on these findings, it appears that water quality and stream ecological integrity may be most at risk in North Carolina watersheds where a higher amount of urban development is occurring at the watershed scale, where a lower percentage of forest cover exists in riparian corridors, and where the topography is generally flatter. The ecological risk assessment process that produced these results was relatively simple and inexpensive. The results are straightforward and generally easy to interpret. The vulnerability model equations that resulted from this assessment process can provide a basis for quantitatively comparing, ranking, and prioritizing risks, which can be useful in cost-benefit and cost-effectiveness analyses of alternative management options. Specifically, they offer a useful approach for characterizing the risk of potential land management options through the simulation of land use change, such as conversion of land cover or implementation of best management practices.