Start Date

14-2-2013 11:05 AM

Description

Eastern hemlock (Tsuga canadensis) is an evergreen conifer with a contiguous distribution extending from the southern Appalachian Mountains north to Nova Scotia and west across the Great Lakes region. Eastern hemlock is threatened with extirpation from much of this range by an introduced pest, the hemlock woolly adelgid (Orwig et al. 2002). In addition to the contiguous distribution, many small, isolated populations are located within the central hardwood forest region of Kentucky, Indiana, and Ohio (Braun 1928, Potzger and Friesner 1937, Van Stockum 1979). These disjunct populations form clearly delineated, often monospecific stands associated with unique natural features such as north facing cliff s and box canyons (Hart and Shankman 2005). Disjunct populations have long been of interest to biologists and two primary hypotheses for their origin have been proposed: 1) They are the product of rare long distance dispersal events (Gamache et al. 2003, Nathan 2006), or, 2) Remnants of what was once a portion of the contiguous distribution (Daubenmire 1931, Richardson et al. 2002). If long distance dispersal was responsible for the formation of these populations, we predict the resulting genetic bottlenecks to result in low within-population diversity, a correlation by distance to source populations and large between-population differences. Conversely, if these populations represent post-glacial relicts, we predict within population diversity to be dependent on population size, no correlation by distance to source populations, and low between-population differences.

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Feb 14th, 11:05 AM

Disjunct Eastern Hemlock Populations of the Central Hardwood Forests: Ancient Relicts or Recent Long Distance Dispersal Events?

Eastern hemlock (Tsuga canadensis) is an evergreen conifer with a contiguous distribution extending from the southern Appalachian Mountains north to Nova Scotia and west across the Great Lakes region. Eastern hemlock is threatened with extirpation from much of this range by an introduced pest, the hemlock woolly adelgid (Orwig et al. 2002). In addition to the contiguous distribution, many small, isolated populations are located within the central hardwood forest region of Kentucky, Indiana, and Ohio (Braun 1928, Potzger and Friesner 1937, Van Stockum 1979). These disjunct populations form clearly delineated, often monospecific stands associated with unique natural features such as north facing cliff s and box canyons (Hart and Shankman 2005). Disjunct populations have long been of interest to biologists and two primary hypotheses for their origin have been proposed: 1) They are the product of rare long distance dispersal events (Gamache et al. 2003, Nathan 2006), or, 2) Remnants of what was once a portion of the contiguous distribution (Daubenmire 1931, Richardson et al. 2002). If long distance dispersal was responsible for the formation of these populations, we predict the resulting genetic bottlenecks to result in low within-population diversity, a correlation by distance to source populations and large between-population differences. Conversely, if these populations represent post-glacial relicts, we predict within population diversity to be dependent on population size, no correlation by distance to source populations, and low between-population differences.